Greg Cochran points out new research showing that freed from the Malthusian Trap French Canadians underwent natural selection that selected for genes for earlier reproduction.
French Canadian researchers have shown that natural selection has noticeably sped up reproduction among the inhabitants of Île aux Coudres, an island in the St. Lawrence River – in less than 150 years. Between 1799 and 1940, the age at which women had their first child dropped from 26 to 22, and analysis shows this is due to genetic change.
This has to be the case for French Canada generally. There were about 5,000 permanent settlers, including 1600 women: they account for about 90% of the ancestry of the 7 million Francophones in Quebec (along with a substantial number in New England). During that rapid expansion, genes that favored fast reproduction surely increased in frequency. Today the French of Quebec must differ significantly (in those genes that influence this trait) from people in France, which has had relatively slow population growth. Slower reproduction must be favored – lead to greater fitness – in a more Malthusian society.
The Amish population is currently doubling at a 14 year rate. Any small population that can maintain a high rate of doubling will eventually become a very large population. If the very high fertility groups (ethnies?) in developed countries maintain their high fertility rates for the next couple hundred years they'll swamp the rest of the populations of these countries.
The power of natural selection makes me skeptical that industrialized countries will remain outside the Malthusian Trap.
You are a mutant. Don't deny it. Accept your role in the mutant horde.
Each one of us receives approximately 60 new mutations in our genome from our parents.
This striking value is reported in the first-ever direct measure of new mutations coming from mother and father in whole human genomes published today.
For the first time, researchers have been able to answer the questions: how many new mutations does a child have and did most of them come from mum or dad? The researchers measured directly the numbers of mutations in two families, using whole genome sequences from the 1000 Genomes Project. The results also reveal that human genomes, like all genomes, are changed by the forces of mutation: our DNA is altered by differences in its code from that of our parents. Mutations that occur in sperm or egg cells will be 'new' mutations not seen in our parents.
The vast majority of those mutations are not in areas that affect gene expression or protein structure. But you might have a unique functional mutation. Do you feel really really weird? A mutation might explain it. Your body might be subtly twisted and strange and foreign to the rest of the human race. You might want to keep that to yourself.
In a very unexpected result some get far more mutations from their fathers and others from their mothers. Why should this be?
They sorted the mutations into those that occurred during the production of sperm or eggs of the parents and those that may have occurred during the life of the child: it is the mutation rate in sperm or eggs that is important in evolution. Remarkably, in one family 92 per cent of the mutations derived from the father, whereas in the other family only 36 per cent were from the father.
With full genome sequencing costs below $10k and dropping rapidly we are only a few years away from being able to find out just how unique we all are.
Some have theorized that the Y chromosome is in decline, that the chromosome that makes men into men is losing out in the rush of evolution. But no. I'm sure many guys will be happy to know that the Y chromosome is evolving under heavy evolutionary pressure.
CAMBRIDGE, Mass. (January 13, 2010) – Contrary to a widely held scientific theory that the mammalian Y chromosome is slowly decaying or stagnating, new evidence suggests that in fact the Y is actually evolving quite rapidly through continuous, wholesale renovation.
By conducting the first comprehensive interspecies comparison of Y chromosomes, Whitehead Institute researchers have found considerable differences in the genetic sequences of the human and chimpanzee Ys—an indication that these chromosomes have evolved more quickly than the rest of their respective genomes over the 6 million years since they emerged from a common ancestor. The findings are published online this week in the journal Nature.
"The region of the Y that is evolving the fastest is the part that plays a role in sperm production," say Jennifer Hughes, first author on the Nature paper and a postdoctoral researcher in Whitehead Institute Director David Page's lab. "The rest of the Y is evolving more like the rest of the genome, only a little bit faster."
A lot of other versions of the Y chromosome fell by the wayside so that our versions could emerge victorious over all those loser Ys. This should not be surprising. One guy can knock up a lot of women. The competition between males to reproduce is much stiffer than the competition between females. More Y chromosomes than X chromosomes lose the race to reproduce in each generation.
The Y chromosome is undergoing renovation.
The results overturned the expectation that the chimp and human Y chromosomes would be highly similar. Instead, they differ remarkably in their structure and gene content. The chimp Y, for example, has lost one third to one half of the human Y chromosome genes--a significant change in a relatively short period of time. Page points out that this is not all about gene decay or loss. He likens the Y chromosome changes to a home undergoing continual renovation.
"People are living in the house, but there's always some room that's being demolished and reconstructed," says Page, who is also a Howard Hughes Medical Institute investigator. "And this is not the norm for the genome as a whole."
Human evolution has been happening quite rapidly. Once genetic testing for embryo selection becomes widespread human evolution will accelerate at a much faster rate than that seen in the recent 10,000 year explosion. The next decade will witness an explosion of human genetic revelations which (in addition to upending politically correct ideologies) will enable people to select embryos that contain much more optimal genetic variations. This will reduce the risk of having offspring not as good looking, healthy, or bright as their parents. Newer generations will be better looking, healthier, and smarter.
Here's a study that finds that humans are still under selective pressure.
Durham, NC – Although advances in medical care have improved standards of living over time, humans aren't entirely sheltered from the forces of natural selection, a new study shows.
"There is this idea that because medicine has been so good at reducing mortality rates, that means that natural selection is no longer operating in humans," said Stephen Stearns of Yale University. A recent analysis by Stearns and colleagues turns this idea on its head. As part of a working group sponsored by the National Evolutionary Synthesis Center in Durham, NC, the team of researchers decided to find out if natural selection — a major driving force of evolution — is still at work in humans today. The result? Human evolution hasn't ground to a halt. In fact, we're likely to evolve at roughly the same rates as other living things, findings suggest.
Taking advantage of data collected as part of a 60-year study of more than 2000 North American women in the Framingham Heart Study, the researchers analyzed a handful of traits important to human health. By measuring the effects of these traits on the number of children the women had over their lifetime, the researchers were able to estimate the strength of selection and make short-term predictions about how each trait might evolve in the future. After adjusting for factors such as education and smoking, their models predict that the descendents of these women will be slightly shorter and heavier, will have lower blood pressure and cholesterol, will have their first child at a younger age, and will reach menopause later in life.
"The take-home message is that humans are currently evolving," said Stearns. "Natural selection is still operating."
Higher fertility is being selected for. But that's to be expected. Selective pressures work to boost reproductive fitness. In an environment where humans are not faced with starvation or much disease it makes sense that selective pressures will work toward reversing declining fertility.
Unless either robots take over or a world government controls human reproduction I expect long term human population growth to push humanity back up against Malthusian limits.
In industrialized countries fertility rates have dropped. But I consider this a temporary phase. Selective pressures will increase the frequency of alleles that boost fertility. Much like Elvis, Darwin is everywhere. An Australian twins study (see here and here) found evidence that alleles that boost fertility are getting selected for in Western populations. Here are the reasons I expect to see rises in fertility in industrialized countries:
- Selective pressures will increase the frequency of alleles that cause women to have more babies.
- Continued advances in reproductive technology will allow infertile women to have babies and for older women to have babies.
- The development of rejuvenation therapies will eventually allow women to remain young and fertile for centuries. The reproductive potential of each woman will skyrocket.
- Some parents will genetically engineer their offspring to want to have kids and the parents will do that to ensure they'll get desired grandchildren.
- Some religious cults will arise that are very pro-fertility.
We've each got our own unique genetic mutations. Each person has 100-200 new genetic mutations that their parents did not have.
Scientists at the Wellcome Trust Sanger Institute and colleagues have made the first direct measurement of the general rate of genetic mutation in humans.
They calculated that there are 100-200 new DNA mutations (single base changes in our DNA sequence that are different from the sequence inherited from our parents) from generation to generation. Almost all were harmless, with no apparent effect on our health or appearance, and only four mutations accumulated over 13 generations.
The findings and method developed by the researchers furthers our understanding of mutation rates and could help us test ways to help reduce mutations. Mutation is the source of genetic variation, which can lead to diseases such as cancer. They also provide a ‘molecular clock’ for measuring evolutionary timescales.
I expect the use of in vitro fertilization (IVF) combined with pre-implantation genetic testing to reduce the frequency of new functionally significant mutations in offspring. As we learn more about the functional meaning of genetic variations (driven by huge declines in DNA sequencing costs) people will increasingly use the discoveries to guide embryo choices with IVF.
The researchers looked at Y chromosomes. This means they missed the accumulation of lethal recessive mutations that can only occur on chromosomes other than the Y chromosome. But they were still able to get a good picture of the rate of mutation. Keep in mind their sample set was small. One would need to repeat this experiment with more people to get a more precise idea of the range of rates of mutation accumulation.
In the new study, the researchers looked at the Y chromosomes of two Chinese men born 13 generations apart. The Y chromosome is passed unchanged from father to son, so mutations accumulate slowly over generations.
The researchers sequenced the chromosomes and compared them with the reference sequence from the original human genome project to find single base pair differences in the sequence.
They found four significant mutations between the Y chromosomes of the two men, despite the many generations of separation. They then calculated that the rate of mutation is equivalent to one mutation in every 15-30 million nucleotides.
“These four mutations gave us the exact mutation rate - one in 30 million nucleotides each generation - that we had expected,” said Dr Tyler-Smith.
The generation of all these mutations eventually results in functionally significant mutations. Of those which have functional significance most are harmful. Some cause death during fetal development or at a young age after birth. Others make people debilitated in various ways. A much smaller number enhance or alter performance in ways that are advantageous in some environments.
As humans spread out across the planet and encountered different environments, diseases, dangers, and food sources selective pressures on humans changed and human evolution accelerated in order to adapt us to local niches. As we developed early technologies and civilizations we exerted even stronger selective pressures on ourselves. In their book The 10,000 Year Explosion: How Civilization Accelerated Human Evolution Gregory Cochran and Henry Harpending explain that we evolved more rapidly as a consequence of our own evolution. If you look around you can spot signs that selective pressures are at work today.
3 genes have been identified that appear unique to humans and we might have a total of 18 genes unique to us.
In this work, David Knowles and Aoife McLysaght of the Smurfit Institute of Genetics at Trinity College Dublin undertook the painstaking task of finding protein-coding genes in the human genome that are absent from the chimp genome. Once they had performed a rigorous search and systematically ruled out false results, their list of candidate genes was trimmed down to just three. Then came the next challenge. "We needed to demonstrate that the DNA in human is really active as a gene," said McLysaght.
The authors gathered evidence from other studies that these three genes are actively transcribed and translated into proteins, but furthermore, they needed to show that the corresponding DNA sequences in other primates are inactive. They found that these DNA sequences in several species of apes and monkeys contained differences that would likely disable a protein-coding gene, suggesting that these genes were inactive in the ancestral primate.
The authors also note that because of the strict set of filters employed, only about 20% of human genes were amenable to analysis. Therefore they estimate there may be approximately 18 human-specific genes that have arisen from non-coding DNA during human evolution.
One wonders whether these regions became active with an initial benefit or did the functional value of the translated regions come later?
These results may seem far-fetched. But a mutation that would cause a previously unused part of the genome to start getting translated into protein might happen in an area which originally came from a viral infection. A portion of viral DNA might have been incorporated into the genome. Also, many more inactive areas of the genome have gotten mutated into activity that caused no benefit or even harm. These few regions that went on to become useful genes arose out of a background of a much larger number of mutations that didn't produce anything useful.
Once we start genetically engineering ourselves the initial changes will involve adding sequences that some people already have. For example, women will want to genetically engineer their melanocytes to produce red or blond hair for example. Also, some men will get genetic engineering for more muscle. These will involve existing genetic sequences already present in the human population.
When things will get really interesting: A much deeper understanding of the functional purposes of genes from other species will turn up many features we do not have that some people will want for themselves or their offspring. When the first genetic transplant from another species into humans is done what will it be done for?
A recent research report entitled "Copy number variation in African Americans" looks at racial differences in DNA sequence differences for what are called copy number variations (CNVs). A CNV is where a big stretch of DNA gets duplicated 1 or more times in some but not all people. CNVs can amplify the expression of a gene by making more copies available for translation into peptides and into regulatory sequences. CNVs are a big deal.
Joseph P McElroy and colleagues from the Department of Neurology, University of California at San Francisco, recruited African Americans from 28 States and used their genomes to draw CNV comparisons with the White dataset. "To the best of our knowledge, this is the first detailed map of copy number variations in African Americans. Understanding the distributions of CNVs in a population is a first step to addressing their role in disease".
The authors employed an array of over 500,000 sequences whose position in the human genome is already known due to single nucleotide polymorphisms. They first analysed the interaction of 50 blood samples of healthy African American females with this gene chip platform, and then used the results as a reference to assess copy number variation in samples from a further 385 African Americans, and an additional set of samples from 435 White individuals. In total, 1362 CNVs were detected in African Americans and 1972 in the White cohort. Across most of the genome, the frequency of CNVs did not differ greatly between the two populations. However, there were two duplications, one on chromosome 15, and one on chromosome 17, whose frequency varied markedly between the two groups.
The research team discovered that the duplication in chromosome 17 (region 17q21) is present in 45% of White but only in 8% of African American individuals. Another independent study has implicated the same region in mental retardation caused by a deletion due to duplication. Among the deleted genes, two of them, CRHR1 (corticitropin releasing hormone receptor 1) and MAPT (microtubule-associated protein tau), were previously associated with some neurological disorders. These two genes are not contained within the 17q21 region of CNV duplication, but map very close to it.
Geneticists are way ahead in identifying genetic differences in contrast to their understanding of what the differences mean. Also, geneticists know more about single letter genetic differences (single nucleotide polymorphisms or SNPs) than they do about these copy number variations (CNVs). The technology for detecting SNPs advanced sooner than the technology for detecting CNVs. But now we are at a point where the costs of detecting SNPs and CNVs are plummeting and we can expect a huge flood of data on genetic differences in the next several years. We can also expect a big flood of discoveries for what it all means. Prepare yourself for a big change in our understanding of human nature and human evolution.
An excellent recent book, The 10,000 Year Explosion: How Civilization Accelerated Human Evolution, argues that human evolution accelerated by a factor of 100 over the last 10,000 years and that humans have undergone substantial amounts of natural selection to adjust for local conditions. So some of the large copy variations discovered above which are specific to one race or the other probably adapted our ancestors to local conditions in a variety of fashions including toxin processing, immune response to local diseases, digestive adjustments to locally available foods, adjustments to climates, and assorted other adaptations.
Selective abortion of female fetuses is common in China, India, and some other Asian countries. A Plos One report finds that Vietnam shows signs of following the same pattern with a rise in the number of male births to 100 female births (Sex Ratio at Birth or SRB).
Birth history statistics indicate that the SRB in Viet Nam has recorded a steady growth since 2001. Starting from a level probably close to the biological standard of 105, the SRB reached 108 in 2005 and 112 in 2006, a value significantly above the normal level. An independent confirmation of these results comes from the surveys of births in health facilities which yielded a SRB of 110 in 2006–07. High SRB is linked to various factors such as access to modern health care, number of prenatal visits, level of higher education and employment status, young age, province of residence and prenatal sex determination. These results suggest that prenatal sex determination followed by selective abortion has recently become more common in Viet Nam. This recent trend is a consequence of various factors such as preference for sons, declining fertility, easy access to abortion, economic development as well as the increased availability of ultrasonography facilities.
One potential problem from a surplus of males is obviously more violence. All the single guys competing for women and feeling sexual frustration can cause problems.
But there's an evolutionary angle that is more interesting. The surplus of males heightens competition for reproductive resources (i.e. women) and therefore heightens selective pressures. One might expect economically more successful men to have an advantage in such a situation. If so, the effect will be to select for genes that code for smarter, more ambitious, and more driven males.
Natural selection in the human race has not stopped. Blogger Audacious Epigone uncovers an interesting pattern in General Social Survey data. Those with firm belief in God and those with firm belief God doesn't exist make more babies. My take: the genes for doubt and skepticism are getting selected against.
The great back-and-forth between Jason Malloy and Bruce G. Charlton led me to wonder if the trend of increased fertility as theistic confidence increases conscious, or if it a subconscious and indirect consequence of values and behaviors not explicitly related to a person's stated ideal family size. BGC suggested that secular women do not just have fewer children than the religious do, but that this stems from a desire to have fewer children to begin with.
From GSS data, I looked at the reported ideal family size* and the actual number of children had, by theistic confidence, among those who had essentially completed their total fertility (age 40-100):
Theistic confidence Desired Actual Don't believe 2.26 2.23 No way to find out 2.25 1.95 Some higher power 2.18 1.98 Believe sometimes 2.37 2.34 Believe with doubts 2.34 2.31 Know God exists 2.58 2.64
The more theistic, the greater the number of ideal children for a completed family to contain. It tracks almost identically with the actual number of children given birth to. That's not too surprising, since people are probably biased towards defining their actual family size as the ideal family size.
Granted, those who believe in God surpass the atheists in fertility. But the biggest doubters have the lowest fertility levels. Either the feeling of certainty boosts fertility or some factor causes both certainty and higher fertility.
As long time readers know one of my interests in the future has to do with which way will human evolution go? The DNA sequencing evidence already points int the direction that human evolution has already accelerated by orders of magnitude in the last 10,000 years and we aren't the same humans as those who walked the Earth even a few thousand years ago. An excellent recent book, The 10,000 Year Explosion: How Civilization Accelerated Human Evolution, explores these findings in greater detail.
But what of the future? My fear is that the human race will splinter into subspecies that have cognitive dissimilarities that lead to wars of enormous lethality on a scale beyond any wars to date. Will genetic engineering for higher IQ give us the insights to doubt our own feelings of certainty and do a better job of seeing the viewpoints of others? Or will some faction of future transhumans use their greater intellectual abilities to ruthlessly pursue the triumph of their genetically engineered extremely strongly felt moral preferences?
Evolutionary theorist Greg Cochran and genetic anthropologist Henry Harpending have teamed up again and with John Hawks, Eric Wang, and Robert Moyzis to argue that human evolution has greatly accelerated in the last 10,000 years and the human race is diverging.
Dec. 10, 2007 - Researchers discovered genetic evidence that human evolution is speeding up - and has not halted or proceeded at a constant rate, as had been thought - indicating that humans on different continents are becoming increasingly different.
"We used a new genomic technology to show that humans are evolving rapidly, and that the pace of change has accelerated a lot in the last 40,000 years, especially since the end of the Ice Age roughly 10,000 years ago," says research team leader Henry Harpending, a distinguished professor of anthropology at the University of Utah.
Harpending says there are provocative implications from the study, published online Monday, Dec. 10 in the journal Proceedings of the National Academy of Sciences:
- "We aren't the same as people even 1,000 or 2,000 years ago," he says, which may explain, for example, part of the difference between Viking invaders and their peaceful Swedish descendants. "The dogma has been these are cultural fluctuations, but almost any Temperament trait you look at is under strong genetic influence."
- "Human races are evolving away from each other," Harpending says. "Genes are evolving fast in Europe, Asia and Africa, but almost all of these are unique to their continent of origin. We are getting less alike, not merging into a single, mixed humanity." He says that is happening because humans dispersed from Africa to other regions 40,000 years ago, "and there has not been much flow of genes between the regions since then."
"Our study denies the widely held assumption or belief that modern humans [those who widely adopted advanced tools and art] appeared 40,000 years ago, have not changed since and that we are all pretty much the same. We show that humans are changing relatively rapidly on a scale of centuries to millennia, and that these changes are different in different continental groups."
The increase in human population from millions to billions in the last 10,000 years accelerated the rate of evolution because "we were in new environments to which we needed to adapt," Harpending adds. "And with a larger population, more mutations occurred."
Study co-author Gregory M. Cochran says: "History looks more and more like a science fiction novel in which mutants repeatedly arose and displaced normal humans - sometimes quietly, by surviving starvation and disease better, sometimes as a conquering horde. And we are those mutants."
Harpending conducted the study with Cochran, a New Mexico physicist, self-taught evolutionary biologist and adjunct professor of anthropology at the University of Utah; anthropologist John Hawks, a former Utah postdoctoral researcher now at the University of Wisconsin, Madison; geneticist Eric Wang of Affymetrix, Inc. in Santa Clara, Calif.; and biochemist Robert Moyzis of the University of California, Irvine.
Using data from the International Haplotype Map Project on single nucleotide polymorphisms (SNPs which are single letter genetic differences)
Harpending and colleagues used a computer to scan the data for chromosome segments that had identical SNP patterns and thus had not broken and recombined, meaning they evolved recently. They also calculated how recently the genes evolved. A key finding: 7 percent of human genes are undergoing rapid, recent evolution.
So we are becoming less alike due to adaptations to local environments. My guess is this trend will accelerate when offspring genetic engineering becomes possible. People in different cultures, religions, climates, occupations, social classes, and regulatory environments will make different decisions on which genetic variations to give their offspring. As a result groups will become less alike. Some groups will choose genes that enhance analytical ability and mathematical skills. Some will emphasize genes that boost ambition and perhaps even ruthlessness. Others will go for genetic variations that increase moral motivation and spirituality.
Update: The divergence of human genomes is a result of growing human populations moving into lots of different habitats that each exert different selective pressures. The selective pressures operated on immune systems, musculature, hair, skin, brains, and many other aspects of human shape and physiology.
It says something about the adaptive value of specific temperaments to specific habitats that these researchers report big selective pressures on genes that control temperament. That makes sense if you think about it intuitively. A hunter probably needs a different temperament than a goat herder (who experiences a lot of solitude) who needs a different temperament than a merchant (who interacts with many other humans and needs to enjoy sizing them up quickly). Some tasks are far more cognitively demanding than others. Some tasks require much more hand-eye coordination or better balance or more strength or endurance. Humans working at different tasks to survive in different environments got selected to be shorter or taller, better sprinters or better long distance runners, more muscular or fatty or skinny, and many other attributes. This is akin to specialization of labor.
See the John Hawks introduction to the paper on his blog. Also see his "Acceleration rarely asked questions" about the research. Hawks says the selective pressures acting on human genomes have been so strong in recent history that the signal they are measuring is larger than the biases one might expect would make the data hard to interpret.
In the earliest studies, when people were finding that 3 or 4 percent of a sample of genes had signs of recent selection, those numbers were already extremely high. They got even higher, as more and more powerful methods of detecting selection came online. Our current estimate is the highest yet, but even this very high number is perfectly consistent with theoretical predictions coming from human population numbers.
At one level, the mathematical answer is as simple as "more people means more mutations." But more deeply, we can predict a linear response of new selected alleles to population size, and we can model this response with respect to a particular frequency range. The genome is a complicated place -- with different mutations originating at different times, selected at different strengths, consequently with different fixation probabilities and different current frequencies. For some reason, nobody really tried to describe this mathematically before.
Now, our model is extremely simple -- it can be challenged on several specific bases. For instance, population increase was not a simple exponential -- it grew in fits and starts, with some significant crashes. The average strength of selected mutations probably changed over time, and the distribution of the strength of selection may have departed from our assumptions. Even the adaptive mutation rate may have changed over time.
Still, the general prediction is quite clear: the population has grown, its conditions of existence have changed, and as a result selection on new mutations should have accelerated. And the observed data fit our theoretical prediction exceptionally well. Certainly we could do better if we made a more detailed model, and we will be doing some of that in future papers. But mathematical simplicity has a great virtue: we can see precisely why human historical changes should have accelerated this aspect of our evolution, and we can see the magnitude of the response. That magnitude greatly outweighs all potential biases.
Go read the full Hawks post. It is all worth reading.
March 2009 Update: This work has since become the basis for an excellent book by Cochran and Harpending entitled The 10,000 Year Explosion: How Civilization Accelerated Human Evolution.
Geico should run a cave man commercial with a red head cave man. Or one of the caveman TV show actors should have red hair.
CAMBRIDGE, Mass. -- Ancient DNA retrieved from the bones of two Neanderthals suggests that at least some of them had red hair and pale skin, scientists report this week in the journal Science. The international team says that Neanderthals' pigmentation may even have been as varied as that of modern humans, and that at least 1 percent of Neanderthals were likely redheads.
The scientists -- led by Holger Römpler of Harvard University and the University of Leipzig, Carles Lalueza-Fox of the University of Barcelona, and Michael Hofreiter of the Max Planck Institute for Evolutionary Anthropology in Leipzig -- extracted, amplified, and sequenced a pigmentation gene called MC1R from the bones of a 43,000-year-old Neanderthal from El Sidrón, Spain, and a 50,000-year-old individual from Monti Lessini, Italy.
"Together with other genes, this MC1R gene dictates hair and skin color in humans and other mammals," says Römpler, a postdoctoral researcher working with Hopi E. Hoekstra in Harvard's Department of Organismic and Evolutionary Biology. "The two Neanderthal individuals we studied showed a point mutation not seen in modern humans. When we induced such a mutation in human cells, we found that it impaired MC1R activity, a condition that leads to red hair and pale skin in modern humans."
Evolutionary theorist Gregory Cochran and anthropologist John Hawks claim to have found evidence of a huge increase in the rate of human evolution in the more recent period of human evolution of the last 40,000 years.
Human evolution has been speeding up tremendously, a new study contends—so much, that the latest evolutionary changes seem to largely eclipse earlier ones that accompanied modern man’s “origin.”
Contrary to the common view that humans have changed little since out-of-Africa Cochran and Hawks think big changes have come since humans emerged as a distinct species.
“The origin of modern humans was a minor event compared to more recent evolutionary changes,” wrote the authors of the research, in a presentation slated for Friday in Philadelphia at the annual meeting of the American Association of Physical Anthropologists.
Cochran and Hawks see a 2 orders of magnitude acceleration in human evolution in the last 40,000 years.
Hawks and Cochran analyzed measurements of skulls from Europe, Jordan, Nubia, South Africa, and China in the past 10,000 years, a period known as the Holocene era. They also studied European and West Asian skulls from the end of the Pleistocene era, which lasted from two million years ago until the Holocene.
“A constellation of features” changed across the board, Hawks and Cochran wrote in their presentation. “Holocene changes were similar in pattern and... faster than those at the archaic-modern transition,” the time when so-called modern humans appeared. But these changes “themselves were rapid compared to earlier hominid evolution.” Hominids are a family of primates that includes humans and their extinct, more ape-like though upright-walking ancestors and relatives.
Hawks and Cochran also analyzed past genetic studies to estimate the rate of production of genes that undergo positive selection—that is, genes that spread because they are beneficial. “The rate of generation of positively selected genes has increased as much as a hundredfold during the past 40,000 years,” they wrote.
Humans were already spread over large areas of land 40,000 years ago and were evolving to better fit their local environments. If human evolution has been rapid then different population groups likely possess important unique adaptations to local circumstances and the differences between groups are larger than politically correct people would like us to believe.
This reminds me of a recent paper in Nature Genetics that found a quarter of genes show different expression levels in Europeans and East Asians.
Ethnicity stems not just from differences in genetic sequence, but also from differences in the expression of genes shared by ethnic groups, according to a new study in Nature Genetics. The authors found that 25 percent of genes show different expression levels in Asian and European individuals, and single-nucleotide polymorphisms (SNPs) in regulatory elements likely account for many of these variations.
To see if some of these polymorphisms could cause differences in gene expression levels, researchers led by Richard Spielman of the University of Pennsylvania in Philadelphia assayed gene expression differences between ethnic groups.
Spielman and his colleagues measured expression levels of more than 4,000 genes in lymphoblastoid cell lines derived from individuals from three different populations: Chinese, Japanese, and European. They found that gene expression levels from the Chinese and Japanese groups were largely the same, but that expression levels between the Asian groups and the European group differed significantly for more than 1,000 genes.
Local selective pressures produced so many differences.
Also see the March 2006 Plos Biology paper A Map of Recent Positive Selection in the Human Genome by Jonathan K. Pritchard and colleagues at the University of Chicago.
Cheaper DNA testing technologies are going to produce a huge flood of reports on human evolution and human differences.
March 2009 Update: This work has since become the basis for an excellent book by Cochran and Harpending entitled The 10,000 Year Explosion: How Civilization Accelerated Human Evolution.
Toshihiko Komatsu, a functional anatomist at Osaka University in Japan, found in a study of dissection results that where most humans have 2 muscles as upper arm biceps some people have 3 or even 4 bicep muscles. (triceps? quadraceps?)
However, in Komatsu's research, 14 to 20 percent of people were found to have three muscles and 1 to 4 percent were found to have four muscles in their biceps.
People with more than the usual two muscles also tended to have more muscles than normal in other parts of their body, such as their elbows or fingers.
Do some people have genetic variations that code for more muscles? Or does noise in the system cause some small fraction of developing embryos to grow extra muscles in assorted places?
If people who have extra muscles are symmetric in their muscle counts (e.g. 3 muscles on upper arms on both arms) then that tends to suggest genetic variations coding for this result.
Any time you read about people who deviate from the biological norm for some quality of their bodies keep in mind that anything that can happen naturally will some day become selectable using biotechnology. If the people who have extra muscles gain some performance advantage then expect some parents in the future to opt for genetic engineering to give their kids the extra muscles on purpose.
Adding extra muscles to adults will become possible when advances in stem cell research and tissue engineering provide the ability to grow replacement muscles either inside or outside the body. But making those muscles useful might be much harder because wiring up neurons to the muscles and then training the brain to control them appropriately could turn out to be quite difficult.
The Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, in collaboration with 454 Life Sciences Corporation, in Branford, Connecticut, today announce a plan to have a first draft of the Homo neanderthalensis genome within two years.
Come on guys. Some day some group is going to use human eggs to put neanderthal DNA made with DNA synthesis machines to create neanderthal babies. Your work is laying the foundations. We should consider what will be the consequencs. Will the Neanderthal facilty for speech be good enough for them to sing? I want to hear neanderthals cover the Kinks classic "I'm an ape man, I'm an ape ape man, I'm an ape man. I'm a king kong man, I'm a voodoo man, I'm an ape man".
Neanderthals might not make nice semi-people. Would they be smart enough and capable of being civilized enough to qualify for human rights? One of the biggest debates of the 21st century (at least until the robots take over) is going to be on the question of which attributes must an intelligence possess to be eligible for rights and even to be eligible for not immediately getting destroyed or at least imprisoned. But that debate hasn't started in earnest yet because all the politically correct liberals are still denying that genetics plays a big role in creating cognitive characteristics that determine why human societies take the forms we see.
Advances in sequencing technology made by 454 Life Sciences makes the sequencing attempt possible. (same press release here as PDF)
"The Max Planck Institute and 454 Life Sciences are working together to sequence the Neandertal genome. Our expertise with ancient DNA and the Neandertal, coupled with 454 Sequencing, a next generation sequencing technology with unparalleled throughput, makes this an ideal collaboration," explained Svante Paabo, Ph.D., Director of the Department of Evolutionary Anthropology at the Max Planck Institute. "The advent of 454 Sequencing has enabled us to move forward with a project that was previously thought to be impossible."
Neandertal inhabited Europe and the Near East until about 30,000 years ago then disappeared after his successor, Homo sapiens, migrated to Europe. This year marks the 150th anniversary of the discovery of the first Neandertal fossil in Germany's Neander Valley near Dusseldorf. Dr. Paabo was the first to sequence DNA from a Neandertal fossil in 1997 while at the University of Munich.
That these scientists can get DNA fragments good enough to be worth trying to sequence is the amazing part of it.
Extracting, identifying and sequencing ancient DNA from fossils is a technically challenging task. When an organism dies, its tissues are overrun by bacteria and fungi. Much of the DNA is simply destroyed, and the small amount remaining is broken into short pieces and chemically modified during the long period of fossil formation. This means that when scientists mine tiny samples of ancient bones for DNA, much of the DNA obtained is actually from contaminants such as bacteria, fungi and even scientists who have previously handled the bones.
Over the last twenty years, Dr. Paabo's research group has developed methods for demonstrating the authenticity of ancient DNA results, as well as technical solutions to the problems of working with short, chemically-modified DNA fragments. Together with 454 Life Sciences, they will now combine these methods with high-throughput DNA sequencing. By enabling a method of sequencing that is more comprehensive and less expensive than conventional sequencing methods, 454 Sequencing is well suited for such a project.
"Unlike the human genome project, Neandertal samples are extremely scarce and have been contaminated with microbial DNA over tens of thousands of years. Therefore, this project is only possible with 454 Sequencing technology," said Michael Egholm, Ph.D., Vice President, Molecular Biology, 454 Life Sciences.
Due to such sample contamination, the task of sequencing the Neandertal genome is much more extensive than the task of sequencing the human genome. 454 Life Sciences' Genome Sequencer 20 System makes such an endeavor feasible by allowing approximately a quarter of a million single DNA strands from small amounts of bone to be sequenced in only about five hours by a single machine. The DNA sequences determined by the Genome Sequencer 20 System are 100-200 base pairs in length, which coincides neatly with the length of ancient DNA fragments.
Over the next two years, the Neandertal sequencing team will reconstruct a draft of the 3 billion bases that made up the genome of Neandertals. For their work, they will use samples from several Neandertal individuals, including the type of specimen found in 1856 in Neander Valley and a particularly well-preserved Neandertal from Croatia. The Max Planck Society's decision to fund the project is based on an analysis of approximately one million base pairs of nuclear Neandertal DNA from a 45,000-year-old Croatian fossil, sequenced by 454 Life Sciences.
A comparison of human and chimpanzee DNA sequences for large structural variations such as inversions (flips) has led to the discovery of more genetic variations between humans than were previously known.
By comparing the human genome with that of the chimpanzee, man's closest living relative, researchers have discovered that chunks of similar DNA that have been flipped in orientation and reinserted into chromosomes are hundreds of times more common in primates than previously thought. These large structural changes in the genome, called inversions, may account for much of the evolutionary difference between the two species. They may also shed light on genetic changes that lead to human diseases.
Although humans and chimpanzees diverged from one another genetically about six million years ago, the DNA sequences of the two species are approximately 98 percent identical.
...The researchers published their findings in the October 28, 2005, issue of the journal Public Library of Science Genetics (PLoS Genetics).
That previous link is free access.
This paper provides yet more evidence that the early focus on single point mutations (Single Nucleotide Polymorphisms or SNPs) as a measure of genetic variation between humans has understated the extent to which humans differ from each other genetically.
This research expands on a Nature paper published on September 1, 2005, by HHMI investigator Evan E. Eichler at the University of Washington. Eichler's group determined that novel duplications of genetic material within humans also significantly contribute to differences between the species.
Instead of identifying sequence changes between the two genomes at the base-pair level, Scherer focused his research on large structural variations in chromosomes between humans and chimps, specifically genetic inversions. Inversions can disrupt the expression of genes at the point where the chromosome breaks, as well as genes adjacent to breakpoints.
“From a medical genetics perspective, there are probably hundreds of disease genes that have not yet been characterized,” said Scherer. “The vast majority of disease gene discovery has been based on gene sequencing, but this is not a comprehensive view of chromosomes. We are using an evolutionary approach to identify mutations that may predispose people to disease.”
According to Scherer, prior to this research, only nine inversions between humans and chimps had been identified. Using a computational approach, Scherer's group identified 1,576 presumed inversions between the two species, 33 of which span regions larger than 100,000 base pairs—a sizeable chunk of DNA. The average human gene is smaller, only about 60,000 bases in length.
Scherer's team experimentally confirmed 23 out of 27 inversions tested so far. Moreover, by comparing the chimp genome with its ancestor, the gorilla genome, they determined that more than half of the validated inversions flipped sometime during human evolution.
The genetic sequence inversions found in humans are not found uniformly across all humans.
Perhaps even more interesting than the abundance of inversions that Scherer's group unveiled was their discovery that a subset of the inversions are polymorphic—taking different forms—within humans, meaning that the human genome is still evolving. When the 23 experimentally confirmed inversions were tested against a panel of human samples, the scientists found three inversions with two alleles or pairs of genes displaying the human inversion in some people, whereas others had one allele of the human inverted sequence and one allele of the normal sequence in chimps.
Having one allele with an inversion and one allele without represents a ticking time bomb in genetic terms, Scherer said, since these alleles may improperly align and recombine during replication, ultimately causing DNA deletions or a loss of DNA that subsequent generations inherit. Scherer's prior research on Williams-Beuren syndrome, a disease caused by DNA micro-deletions, identified a significantly higher incidence of inversions among the parents of afflicted patients.
Because of the small human population used for comparison by these researchers many more structural variation polymorphisms in humans were probably missed in this report.
Scherer said that his group looked at only a very small subset of the human population when assessing the prevalence of polymorphisms. He suspects that polymorphisms, and structural variations in general, may be much more common than his preliminary analyses suggest.
We need DNA testing methods for easily and cheaply detecting large copy variations, inversions, and other large structural variations. It is obviously not enough just to compare single point mutations as the HapMap project is doing. Lots of important genetic variations exist as larger structural differences. While most of the SNP differences have been identified most of the large structural variations probably still wait discovery.
Also see my recent posts "Human Genetic HapMap Phase I Published" and "Genetic Analysis Shows Signs Of Selective Pressure In Human Evolution".
At the project's outset in October 2002, the consortium set an ambitious goal of creating a human haplotype map, or HapMap, within three years. The Nature paper marks the attainment of that goal with its detailed description of the Phase I HapMap, consisting of more than 1 million markers of genetic variation, called single nucleotide polymorphisms (SNPs). The consortium is also nearing completion of the Phase II HapMap that will contain nearly three times more markers than the initial version and will enable researchers to focus their gene searches even more precisely on specific regions of the genome.
Identification of locations where chromosomes swap sections of genetic code provides a number of benefits. One big advantage is that it allows testing of smaller numbers of locations in order to better guess what sequence variations will be found at untested locations. This lowers the cost of genetic testing. This is great for tracking which genetic sequence variations are correlated with specific diseases, physical body shapes and colors, and cognitive differences among other areas of human differences.
Just because most people who have particular SNPs at particular locations usually also then have particular other SNPs at other locations does not mean this is always the case. Some people will have rarer mutations (in fact we probably all have unique mutations). So the coming decline in cost of DNA sequencing by orders of magnitude will provide useful benefits, especially for identifying rarer mutations and identifying who has those rarer mutations.
Identification of the key SNP locations also provides a sort of roadmap for the study of human evolution. The fact that some sections with common sets of SNPs are shorter and other sections are longer is helpful in identifying genetic functionality that has been under a great deal of selective pressure.
Genetic diversity in humans is increased by recombination, which is the swapping of DNA from the maternal and paternal lines. It has been recently realized that in humans, most such swapping occurs primarily at a limited number of "hotspots" in the genome. By analyzing the HapMap data, the researchers have produced a genome-wide inventory of where recombination takes place. This will enable more detailed studies of this fundamental property of inheritance, as well as serve to improve the design of genetic studies of disease.
The scientists found evidence of selective pressures for both immune response and cognitive function.
The HapMap consortium found that genes involved in immune response and neurological processes are more diverse than those for DNA repair, DNA packaging and cell division. Researchers speculate the difference might be explained by natural selection shaping in the human population in ways that favor increased diversity for genes that influence the body's interactions with the environment, such as those involved in immune response, and that do not favor changes in genes involved in core cellular processes.
As expected, the vast majority of both rare and common patterns of genetic variation were found in all of the populations studied. However, the consortium did find evidence that a very small subset of human genetic variation may be related to selection pressures related to geographic or environmental factors, such as microorganisms that cause infectious diseases. This evidence appears as significant differences in genetic variation patterns in particular genomic regions among the populations studied. While more follow-up study is needed to explore the differences, researchers say some of the most striking examples merely serve to confirm well-known genetic differences among populations, such as the Duffy blood group, which plays a role in response to malaria, and the lactase gene, which influences the ability to digest milk products.
In 20 or 30 years most of the selective pressures that acted on the human race in local environments will probably be well characterised and their effects quantified down at the level of frequencies of genetic variations in different human populations. We are living in the final years of our ignorance of how natural selection molded humans to produce the wide range of human variations we see today.
The HapMap is for single point mutations. But recent progress in identifying larger scale structural variations such as large copy variations is starting to paint a picture of much larger amounts of genetic variation between individuals and groups.
Cornell researcher Carlos Bustamante and associates have found signs of Darwinian selective pressure in recent human evolution.
ITHACA, N.Y. -- The most detailed analysis to date of how humans differ from one another at the DNA level shows strong evidence that natural selection has shaped the recent evolution of our species, according to researchers from Cornell University, Celera Genomics and Celera Diagnostics.
In a study published in the Oct. 20 issue of the journal Nature, Cornell scientists analyzed 11,624 genes, comparing how genes vary not only among 39 humans but also between the humans and a chimpanzee, whose DNA is 99 percent identical to humans.
The comparisons within and between species suggest that about 9 percent of genes that show some variability within humans or differences between humans and chimpanzees have evolved too rapidly to be explained simply by chance. The study suggests that positive Darwinian natural selection -- in which some forms of a gene are favored because they increase the probability of survival or reproduction -- is responsible for the increased rate of evolution. Since genes are blueprints for proteins, positive selection causes changes in the amino acid sequence of the protein for which the gene codes.
I wish the press release on this study provided a bit more detail. How recent is "recent" in this context? For any of the genes are there signs of selective pressure just within the last few thousand years? Also, how many of the genes examined have functions specific to the nervous system and what percentage of them show recent signs of selective pressure?
Cheaper DNA sequencing technologies will eventually enable studies with much larger groups of people, larger numbers of genes, and more types of genetic difference. My guess is this study looked mainly at point mutations and not large copy variations (see the second report below about large copy variations). As large copy variations become more easily testable more signs of selective pressure will be found.
Several categories of genes underwent selective pressure to create modern humans.
"Our study suggests that natural selection has played an important role in patterning the human genome," said the paper's lead author, Carlos Bustamante, assistant professor of biological statistics and computational biology at Cornell.
The Cornell/Celera team found that genes involved in immune function, sperm and egg production, sensory perception and transcription factors (proteins that control which genes are turned on or off) have been particularly affected by positive selection and show rapid evolution in the last 5 million years, when humans shared a common ancestor with chimps.
13 percent of the genes examined appear to be under negative selection against variations that are harmful.
Likewise, the researchers found that approximately 13 percent of the genes that may vary show evidence of slightly deleterious or harmful mutations in human populations; these include genes involved in determining the basic structure of cells and muscles as well as genes that control traffic in and out of the cell. These mutations are subject to weak negative selection, according to the study. In general, negative selection eliminates from the population very harmful changes to proteins that kill or stop reproduction. But mutations that have led to slightly deleterious versions of the gene -- mutations that may cause disease or only slightly reduce the average number of children left by those that carried the mutation -- can by chance become quite common in the population.
Mildly harmful mutations take a long time to get selected out. Identification of purely harmful mutations be very useful in offspring genetic engineering to produce human offspring with far fewer purely harmful genetic mutations. Such humans will function better mentally and physically in a large assortment of ways.
All of us now living are already born with lots of harmful mutations. Well, we are not permanently stuck with old flawed genetic software. In a couple of decades we'll be able to get replacement organs grown which will be grown from stem cells genetically engineered to remove harmful mutations. We'll also be able to get stem cell therapies to upgrade our bodies with better genetic software.
Read this excellent article in Nature which surveys recent discoveries of larger amounts of genetic variation in humans than has previously been predicted.
How common, exactly? Last July, Wigler's group reported that it had looked at 20 normal individuals and found 221 places in the genome where those people had different copy numbers of stretches of DNA2. Some of these copy-number changes showed up in more than one person, and so qualify as 'polymorphisms' — shorthand for particular spots in the genome that regularly differ between individuals. In the Book of Life analogy, these polymorphisms represent sections of text where certain paragraphs are repeated different numbers of times in different individuals.
About 76 of the variations Wigler's team found were polymorphisms, and each person had about 11 of them in his or her genome2. Soon after, Lee and Scherer reported that in a survey of 55 people they had found 255 copy-number variants, 102 of which were polymorphisms3.
Large copy variations can produce large effects. Picture a gene for making a neuroreceptor. An extra copy of it could increase the concentration of that receptor on the end of a neuron. Or the replication of a gene which makes a protein which stimulates neural stem cells to divide could cause more rapid neural stem cell growth and hence larger brains in those who carry extra copies.
In addition to the large copy variations researchers have since found large scale rearrangements, deletions and insertions. Together all these variations are referred to as structural variations. The number of structural variations being discovered is so large that the claim of 99% shared genetic sequences between different humans may turn out to be too high..
Genome researchers now have a catch-all phrase for the vast array of rearrangements — including copy-number polymorphisms, inversions, deletions and duplications — that occur normally in the human genome. They call it structural variation, and have described at least 800 individual variants that, in total, account for about 3.5% of the human genome. And the sheer number of variants seems likely to catch up with the number of known single nucleotide polymorphisms — the single-letter 'typos' in the Book of Life. That makes structural variation a potentially major source of diversity. It is even possible that we're not all 99.9% similar, as the Human Genome Project predicted.
The increasing discoveries of genetic dissimilarity between humans is evidence of selective pressure to adjust to local environments as humans spread out and colonized the globe.
Also see my previous post "Brain Gene Allele Frequences Show Brain Still Evolving".
March 23, 2005 -- Economics-free trade may have contributed to the extinction of Neanderthals 30,000-40,000 years ago, according to a paper published in the "Journal of Economic Organization and Behavior."
"After at least 200,000 years of eking out an existence in glacial Eurasia, the Neanderthal suddenly went extinct," writes University of Wyoming economist Jason Shogren, along with colleagues Richard Horan of Michigan State University and Erwin Bulte from Tilburg University in the Netherlands. "Early modern humans arriving on the scene shortly before are suspected to have been the perpetrator, but exactly how they caused Neanderthal extinction is unknown."
Creating a new kind of caveman economics in their published paper, they argue early modern humans were first to exploit the competitive edge gained from specialization and free trade. With more reliance on free trade, humans increased their activities in culture and technology, while simultaneously out-competing Neanderthals on their joint hunting grounds, the economists say.
Archaeological evidence exists to suggest traveling bands of early humans interacted with each other and that inter-group trading emerged, says Shogren, the Stroock Distinguished Professor of Natural Resource Conservation and Management in the UW College of Business. Early humans, the Aurignations and the Gravettians, imported many raw materials over long ranges and their innovations were widely dispersed. Such exchanges of goods and ideas helped early humans to develop "supergroup social mechanisms." The long-range interchange among different groups kept both cultures going and generated new cultural explosions, Shogren says.
Anthropologists have noted how judicious redistribution of excess resources provides a distinct advantage to "efficient hunters" as measured by factors such as increased survivorship, social prestige, or reproductive opportunities, the researchers say.
Could humans have developed a greater tendency to feel obligated to each other? Imagine genetic mutations that would increase the feeling of obligation when someone does you a favor. Then imagine a family that does more for each other because they all share this mutation and therefore have an edge in survival.
"For instance, it is believed that killing large game became a method of acquiring wealth, and that efficient hunters could build up 'reciprocal obligations' by exchanging food," Shogren says of his research. "Such obligations, and the gains from trade in general, provide strong incentives to search for new technologies. One of the striking features of the archaeological record is that Neanderthal technology was nearly stationary for many thousands of years whereas technology of early humans experienced many innovations."
Adam Smith would not have approved of the Neanderthals.
He says the evidence does not support the concept of division of labor and trade among Neanderthals. While Neanderthals probably cooperated with one another to some extent, the evidence does not support the view that specialization arose from any formal division of labor or that inter- or intra-group trade existed, he says. These practices seem to require all the things that Neanderthals lacked: a more complicated social organization, a degree of innovative behavior, forward planning and the exchange of information, ideas and raw materials.
"Basic economic forces of scarcity and relative costs and benefits have played integral roles in shaping societies throughout recorded human history," Shogren says. "No reason exists today to discount either the presence or potential impact of economics in the pre-historic dawning of humanity."
He suggests that early humans could have prevailed even if humans and Neanderthals were about equally capable -- provided that humans invented the appropriate economic exchange institutions that created greater wealth for the greater good.
Did humans evolve genotypes that supported better communications skills with which to bargain? Or did humans evolve other abilities that facilitated free trade such as a more sophisticated ability to compare the net worth of different physical objects?
"Through trade and specialization, humans could have conquered their niche even if the incumbent party was somewhat stronger, better adjusted to its environment and equipped with a larger brain volume," he says. "If language and symbolic communication facilitated the invention of trade, it enabled humans to turn the tables on their otherwise dominant competitor."
I think the development of language abilities was important for the development of trade. However, I strongly suspect that more was involved. Consider the wide range of social behaviors seen in various species. Some species are loners that meet up only occasionally to mate. Other species exist only in groups and the shapes of those groups and how they relate to each other varies greatly from species to species.
One can easily imagine (since some species are this way) a human-like species that does not like to socialize at all outside of the immediate group. Such a species could only achieve economies of scale in small groups. Whereas another equally smart primate that enjoys socialization across larger boundaries than just a local group would have much greater chances for setting up trade to achieve larger scale division of labor.
A species that focuses a lot of attention on understanding the personalities of other members of the same species would also have advantages for forming trade relations. A trader who has a mind that causes him or her to think about the behavior and personality of others of the same species would be better equipped to notice and remember how well other traders carried out terms of previous trades.
“It’s an intriguing and novel idea,” says Delson. “But it requires stronger support.” He points out that the Gravettians in particular only emerged 28,000 years ago, while the last of the Neanderthals died about 29,000 years ago.
So the Gravettians could not have had very much influence in the extinction of the Neanderthals, he argues. “He also assumes that all they ate was meat, which of course is not true,” he adds.
Whether or not this particular theory about Neanderthal extinction turns out to be correct I predict that human genes that code for a variety of trade-supporting cognitive characteristics will be found. When genetic engineering of offspring becomes possible the future economic order of huiman or post-human society will depend on what decisions parents and governments make about genes that code for cognitive characteristics which affect economic behavior.
If we some day allow free trade between artificially intelligent computers and robots will the resulting competition and specialization of labor drive humans to extinction?
French scientists Charlotte Faurie and Michel Raymond of the University of Montpellier have found in a cross-cultural comparison of rates of left-handedness and violence that lefties occur at a higher rates in more violent societies.
Among the Jula (Dioula) people of Burkina Faso, the most peaceful tribe studied, where the murder rate is 1 in 100,000 annually, left-handers make up 3.4% of the population. But in the Yanomami tribe of Venezuela, where more than 5 in 1,000 meet a violent end each year, southpaws account for 22.6%. Faurie and Raymond report their findings in the Proceedings of the Royal Society.
Many sports are kinda like violence under civilized rules. Well, sports people are more often left-handed than the overall population.
And the ratio of left-handers to right-handers is higher in successful sportspeople than it is in the general population, suggesting there is definite advantage to favouring the left hand or foot in competitive games, such as tennis.
Statistical evidence links several auto-immune diseases, such as inflammatory bowel syndrome and ulcerative colitis, with left-handedness.
Given the downsides there would have to be strong selective pressures to cause left-handedness to happen anyway. So the need to discover a selective pressure for left-handedness already existed before this latest report was published.
As any schoolboy could tell you, winning fights enhances your status. If, in prehistory, this translated into increased reproductive success, it might have been enough to maintain a certain proportion of left-handers in the population, by balancing the costs of being left-handed with the advantages gained in fighting.
Suppose that, as this study suggests, the adaptive value of the ability to fight and win fights differed between societies so strongly that it selected for different frequencies of genetic variations that influence handedness. The existence of differences in selective pressures for competence in human-human violence is especially important because such differences in selective pressure would not have acted only on genes that influence the tendency to be left-handed. Such a difference in selective pressure for violence would also have produced differences in the frequencies of many other genetic variations that influence other aspects of the capacity to commit violent acts (e.g. tendency to impulsivness, ease of angering, muscle strength, and other cognitive and physical qualities).
Here is more evidence that Darwinian natural selection has not stopped operating on humanity as a result of medical advances and rising living standards. Lee Ellis of Minot State University in North Dakota and his student Dan Haman have just published a research paper providing evidence that natural selection is currently selecting for fatter people.
This study sought to determine if genetic factors might be contributing to the increases in the proportions of North Americans who are obese and overweight. The body mass index (BMI) for a large sample of two generations of United States and Canadian subjects was correlated with family fertility indicators. Small but highly significant positive correlations were found between the BMIs of family members and their reproduction rates, especially in the case of women. For instance, mothers in the sample (most of whom were born in the 1940s and 50s) who were in the normal or below normal range had an average of 4·3 siblings and 3·2 children, compared with 4·8 siblings and 3·5 children for mothers who were overweight or obese. When combined with evidence from twin and adoption studies indicating that genes make substantial contributions to obesity, this study suggests that recent increases in obesity are partially the result of overweight and obese women having more children than is true for average and underweight women.
Ellis and Haman speculate that medical advances are allowing obese and diabetic women to live longer to have more children. But that does not explain why overweight women would have more children than skinny women.
So what is going on here? There are a number of possibilities.
One possibility is that one or more of the many hormones being released by fat cells are altering the brain to make women (or their spouses) either more eager or able to have children (possibly by causing them to enter puberty at an earlier stage) or more eager to find a mate or to engage in other behavior that increases reproduction. The hormones from fat cells might even be increasing fertility.
The scientific view of fat cells has changed a lot in recent years and fat cells are now seen as exerting many influences on the rest of the body. There are plenty of hormones being released by adipose fat tissue into the bloodstream. (same article here and here and here)
“When we look at fat tissue now, we see it’s not just a passive depot of fat,” says Dr. Rudolph Leibel of Columbia University. “It’s an active manufacturer of signals to other parts of the body.”
The first real inkling that fat is more than just inert blubber was the discovery 10 years ago of the substance leptin. Scientists were amazed to find that this static-looking flesh helps maintain itself by producing a chemical that regulates appetite.
Roughly 25 different signaling compounds — with names like resistin and adiponectin — are now known to be made by fat cells, Leibel estimates, and many more undoubtedly will be found.
Another possibility is that the obesity is a side effect of a higher fat diet that also boosts hormones and thereby makes girls more fertile or eager to have sex or to have children. This is plausible because a higher fat diet in adolescence raises sex hormones and causes other endocrine changes.
Joanne F. Dorgan, Ph.D., of the Fox Chase Cancer Center in Philadelphia, and her colleagues conducted a study ancillary to the Dietary Intervention Study in Children to examine whether diet influences sex hormone levels during adolescence. The study involved 286 girls ages 8 to 10 who were randomly assigned to a low-fat dietary intervention group or to a group receiving usual care (e.g., educational materials available to the public). The researchers measured blood sex hormone levels at the start of the study and 1, 3, 5, and 7 years later.
After 5 years, girls in the intervention group had 29.8% lower estradiol, 30.2% lower non-sex hormone binding globulin-bound estradiol, 20.7% lower estrone, and 28.7% lower estrone sulfate levels during the first half of their menstrual cycles, and 27.2% higher testosterone levels during the second half of their menstrual cycles,compared with girls in the usual care group. After 7 years, girls in the intervention group had half the progesterone levels during the second half of their menstrual cycles as did girls in the usual care group.
All those hormonal differences must be having some effects on the brain and on the reproductive organs.
Another related possibility comes from the fact that the leptin hormone acts early in life to change the brain to lower inhibition from eating and might also lower the inhibition against having sex. This is just speculation on my part of course. But it is at least plausible.
Another possibility is that obesity is negatively correlated with intelligence and that it is lower intelligence that is responsible for the higher fertility. Of course there are quite smart fat people and plenty of dumb skinny people. But it seems likely that smarter people are, again on average, doing a better job than dumber people of consciously choosing foods and restricting foods in order to manage their weight. Well, if that is the case then selection for obesity may be coming as a side-effect of the existing selective pressures that are obviously selecting against higher levels of intelligence. My guess is that this possibility explains part of the difference in fertility between overweight and skinny people. However, the difference in fertility as a function of educational attainment (which is a decent though not perfect proxy for IQ) appears smaller than the difference as a function of weight. So IQ is probably only one contributing factor.
Another possibility is that overweight people have lower expectations about what they can achieve in looking for a mate and therefore they more quickly decide someone they have found is good enough to settle for. Therefore they start having children sooner and have more children than those who hold out for better mates. Skinnier people probably (and again on average) believe they have a wider selection of choices and may be willing to wait longer to hold out for a still better choice. The delay that comes from waiting may cause them to delay reproduction and therefore reduce the number of children that women in particular can hope to have. Some women wait so long that by the time they are ready to try for a kid they are not even able to start a pregnancy.
Update: Are obese people less bright to begin with? Does lower intelligence cause the risk of obesity to increase? Also, does the direction of causation also run in the opposite direction? Does the presence of obesity cause intellectual abilities to decay? Some researchers think obesity appears to interfere with cognitive function.
Elias, a member of the Statistics and Consulting Unit of BU’s Department of Mathematics and Statistics, and his co-investigators at the Framingham Heart Study are the first to show that long-term, early-onset obesity is an independent risk factor to cognitive dysfunction. This knowledge should help inform physician–patient decisions to treat this physical condition.
Analyses of these data by the researchers found that the combination of obesity and hypertension showed a statistically significant association with the cognitive functioning of men, but not of women. Among late middle-aged and elderly men, obesity and hypertension were associated with lowered cognitive functioning. Among all men, the effects of obesity and hypertension were found to be cumulative, with cognitive functioning lowered more when both conditions were present than when one or neither was a factor. The researchers speculated that obesity and hypertension may have similar physiological “paths” by which they affect cognitive functioning and that the different distribution of fat on men and women may help to explain the adverse effects of obesity in men compared to women.
Stay skinny for your brain. Stay skinny for your heart. Do it to reduce the odds of getting cancer too.
Men and women differed in their participation in reproduction, the researchers report. More men than women get squeezed out of the mating game. As a result, twice as many women as men passed their genes to the next generation.
"It is a pattern that's built up over time. The norm through human evolution is for more women to have children than men," said Jason Wilder, a postdoctoral fellow in UA's Arizona Research Laboratories and lead author on the research articles. "There are men around who aren't able to have children, because they are being outcompeted by more successful males."
Co-author Michael Hammer, a research scientist in UA's Arizona Research Laboratories, said, "We may think of ourselves as a monogamous species, but we're coming from an evolutionary history that's probably slightly polygamous. If we're shifting toward monogamy, it's so recent it hasn't left an imprint on our genome."
Or the same reproductive behavior is continuing, but in a culturally accepted fashion, Wilder said. "The modern version that we generally don't find offensive is that men tend to remarry and have more children much more often than women do."
The team's research also overturns the long-accepted idea that, on average, women's genes traveled farther from their birthplace than did men's. That idea was based on a common marriage practice called patrilocality, wherein women tended to move from their natal village to their husbands' village.
If anything, men and their genes moved farther overall, the new research indicates.
To sort out how far men and women's genes traveled, the UA researchers used DNA from the Y chromosome, which is passed from father to son. Women's lineages were traced using mitochondrial DNA, which passes from mother to daughter.
The researchers report their findings in two related articles, one in the online early edition of the October issue of Nature Genetics and one in an upcoming edition of Molecular Biology and Evolution. The research was funded by the National Institutes of Health.
Scientists have puzzled over the fact that men's common ancestor, dubbed Y-chromosome Adam, seems to have lived around 100 thousand years ago, whereas women's common ancestor, known as mitochondrial Eve, lived almost 200 thousand years ago.
Worldwide, the DNA from the Y chromosome has much less genetic variability than does mitochondrial DNA.
"We wanted to know what shapes the patterns of Y-chromosome and mitochondrial DNA variation," said Wilder. "What can we learn about human behavior?"
To find out, Wilder, Hammer and Zahra Mobasher, a research specialist at UA's Arizona Research Laboratories, tested Y-chromosome DNA and mitochondrial DNA from three far-flung populations of humans: the Khoisan of southern Africa, Mongolian Khalks and highland Papua New Guineans. For each group, DNA from 24 or 25 people was tested.
Previously, researchers assumed equal numbers of men and women procreated. Based on that assumption, scientists explained the relative youth and low variability of the Y chromosome by suggesting that a beneficial mutation on the Y had swept through the whole world. However, the genetic patterns the UA researchers found contradicts those ideas.
If a beneficial mutation had swept through the males, men's common paternal ancestor would be the same age no matter where the UA researchers looked. Instead, the age of men's common ancestor differs between the southern African, Mongolian and Papua New Guinean populations studied. The finding tends to rule out some global beneficial mutation as the reason Y-chromosome DNA is less variable than mitochondrial DNA.
"Because we don't think the pattern we see was caused by an event that swept across the globe, we had to re-examine our assumptions about whether equal numbers of men and women are mating," Wilder said.
The team thinks the genetic patterns are all about sex.
Or lack thereof. Lots more men than women are childless, and it has ever been thus, the researchers say.
My guess is that the legalization and increasing use of divorce has increased the gap between what percentage of women and what percentage of men manage to reproduce in each generation. The most sucessful men have a legally sanctioned way to have a series of wives while the least successful men become street people. Nature is harsh. Why we refer to such an unforgiving and brutal reality as mother nature is beyond me. What is loving and kind about natural selection and evolution in action? Nothing that I can see.
In the longer run people will genetically engineer their offspring. So they will voluntarily reduce the amount of their genetic sequences that they pass along to their offspring. Also, some will clone themselves as a way to increase the amount of their own DNA that they pass along.
Update: Greater female reproductive success is likely to accelerate for another reason. Selective abortion of female fetuses is creating a shortage of female births and adult women in China, in Taiwan, and in India. This trend will probably spread to additional countries as well. A shortage of females will very likely select for genes carried by males who become more successful. Genetic variations that select for intelligence, drive, and a certain degree of masculine aggressiveness will likely be selected for. Physical attractiveness will be selected for more strongly as well. Out-going personalities might also be getting selected for.
Once non-genetic factors such as age, illness, or smoking were removed, a subset of the group seemed to have a blood-oxygen concentration that was 10% higher than normal. This trait was inherited in a way that suggested the difference was due to a single gene.
The researchers also found that the children of women with this putative gene are much more likely to survive to the age of 15, when they are old enough to have children of their own. In the low-oxygen group, each woman had on average 2.5 children that died during childhood. In the high-oxygen group, that average was just 0.4.
The fact that this genetic variation (which has not yet been identified) is under such active selection suggests that it is a variation of fairly recent vintage. A successful adaptation that has been around for a long time in some ecological niche will tend to be present in all organisms of the species which are in that niche unless they have only recently entered that niche. Of course, human conquest where one group wipes out most of another group in some niche could bring the invader group into the niche that the conquered group is already adapted to (even if the conquered group was not well enough adapted to warfare). So the adaptation could have been around for a long time and yet still happen to be getting rapidly selected for in the present time.
Human populations in less developed areas are not the only human groups still undergoing changes in frequencies of genetic variations due to natural selective pressures. All humans are still subject to selective pressures. Darwinian natural selection has not stopped in industrialized countries. What has changed is what is being selected for or against (e.g. intelligence is currently being selected against unfortunately).
The three major human population groups living at high altitudes in Ethiopia, the Himalayas, and the Andes have developed three different sets of adaptations to high altitude living. One reason that their sets of adaptations are different is likely just plain chance. But another reason is that they have not all been living at high altitudes for the same length of time. Initial genetic adaptations are usually not as ideal as adaptations that arise over longer periods of time.
The Andeans, whose lowland ancestors migrated from Asia perhaps 16,000 years ago, adjust to altitude essentially the same way as any lowlander would today -- and it is not a perfect solution.
"Creating more red cells is a pathological response," said Temple University anthropologist Charles Weitz. "If you have too many red cells, the blood's too thick, and it's like pumping oil. Eventually you have to move downhill."
By this same argument athletes who use erythropoietin (EPO) to boost their red blood cell counts are like evolutionary primitives. In the future better understanding of genetic variations for high altitude living will allow athletes to become more like Ethiopians or Himalyan Tibetans.
All of the Tibetans had significantly higher levels of a free radical-fighting enzyme, or antioxidant, called glutathione-S-transferase, and another enzyme, enoyl coenzyme A hydratase, that improves cellular energy production. Tibetans also possessed fewer mitochondria, which are the power manufacturers of cells.
Anthropologist Cynthia Beall of Case Western Reserve University said that Tibetans breathe more per minute than people who live at sea level. Andes residents are able to hold more oxygen in their blood.
Healthy sea-level dwellers have saturations of oxygen in their bloods that vary from 92-100 percent. In the Amabaras sample, the oxygen saturation averaged 95 percent, which surprised Beall, because the oxygen saturation in the Andean and Tibetan highlanders at similar altitudes was in the mid to high 80s.
Of course, once gene therapies and stem cell therapies become feasible then people will be able to have their choice of the best Himalayan and Ethiopian high altitude genetic enhancements. Some will use these enhancements for distance running. Others will enhance in order to do mountaineering. Expect to see extreme mountaineers use genetic engineering to so enhance their oxygen processing capacity that they will be able to easily climb Mount Everest without using supplemental oxygen and without suffering oxygen deprivation symptoms.
RIVERSIDE, Calif. (www.ucr.edu) -- A team of biochemists from UC Riverside published a paper in the June 11 issue of the Journal of Molecular Biology that gives one explanation for why humans and primates are so closely related genetically, but so clearly different biologically and intellectually.
It is an established fact that 98 percent of the DNA, or the code of life, is exactly the same between humans and chimpanzees. So the key to what it means to be human resides in that other 2 percent.
According to Achilles Dugaiczyk, professor of Biochemistry at UCR, one important factor resides in something called Alu DNA repeats, sometimes called "junk DNA." These little understood sections of DNA are volatile, and prone to sudden mutations, or genomic rearrangements. At times the results are beneficial in that they give rise to new proteins or an altered gene regulation. Sometimes the mutations result in the growth of a cancer tumor, or some other genetic defect.
The team, which also included Rosaleen Gibbons, Lars J. Dugaiczyk, Thomas Girke, Brian Duistermars and Rita Zielinski, identified over 2,200 new human specific Alu DNA repeats that are absent from the chimpanzee and most likely other primates.
"The explosive expansion of the DNA repeats and the resulting restructuring of our genetic code may be the clue to what makes us human," Dugaiczyk said. “During the same amount of time, humans accumulated more genetic novelties than chimpanzees, making the human/chimpanzee genetic distance larger than that between the chimpanzee and gorilla.”
Metaphorically speaking, Dugaiczyk said, “Humans and primates march to the rhythm of a drum that looks identical; the same size, shape and sound. But, the human drum beats faster.”
This chemical analysis of DNA structures also showed something else. The spread of the Alu DNA repeats was written into the chemistry of human chromosomes. The process was not random, Dugaiczyk said, and it was not subject to an environmental "natural selection," separating winners and losers as theorized by Darwin.
I question Dugaiczyk's assertion that the spread of Alu repeats was not selected for. Perhaps each repeat's appearance was not selected for. But possibly a mechanism that increased the rate at which Alu repeats accumulated was selected for. Another possibility is that they were selected for in order to move genes around to make certain genes easier to get to for transcription. If the ancestors of humans were under heavier selective pressure once they broke off from chimps then that may have selected for more large scale rearrangements of the 3-D shape of chromosomes in order to allow changes in frequencies of expression of various genes.
Perhaps what the meaning that Dugaiczyk is trying getting to across is being lost by the short length of the press release. Does he think these Alu repeats are having no effect on phenotype and that they represent a spreading of parasitical DNA sequences? It is not clear.
"We are not contending that natural selection does not exist, but that in this instance it is a chemical process within human chromosomes that explains why humans have an explosive expansion of DNA repeats, and primates do not," Dugaiczyk said.
A chemical process? Mediated by enzymes perhaps? What caused those enzymes to start causing more Alu repeats? Did a genetic mutation make Alu repeats more likely to be generated in the germ line? Or did humans come under other selective pressures that by accident were at odds with selecting against accumulation of junk repeat sequences?
Determining the genetic differences between humans and primates is important for several reasons, Dugaiczyk said, including advancing knowledge about how life developed and evolved on earth. Other benefits include making it easier to identifying human predisposition to genetic disease, by comparing humans with other primate species. A third possible benefit is to underline the importance of protecting endangered primate species.
Another advantage to doing comparisons of genetic differences both between and within species is that we can discover the advantages and disadvantages of each variation for the purpose of future genetic engineering. Replace some of one's own parts with better parts. Or create offspring with a collection of advantages that no single human possesses today.
I question whether we really know enough about how many genetic differences there are between species or which ones are most important. Just within the human species the recent discovery of lots of large copy variations (LCVs) effectively more than doubled the previous estimate of how many genetic variations there are between individual humans.
TORONTO -- Scientists at The Hospital for Sick Children (Sick Kids), Brigham and Women's Hospital (BWH) and Harvard Medical School (HMS) have made the unexpected discovery that significant differences can exist in the overall content of DNA and genes contained in individual genomes. These findings, which point to possible new explanations for individual uniqueness as well as why disease develops, are published in the September 2004 issue of the scientific journal Nature Genetics (available online August 1, 2004).
"Using new genome scanning technologies, we serendipitously found stretches of DNA sometimes hundreds of thousands of chemical bases (nucleotides) long that were present or absent in the genomes of healthy individuals. These large-scale copy variations, or LCVs, frequently overlap with genes and could explain why people are different," said Dr. Stephen Scherer, co-principal investigator of the study, a Sick Kids senior scientist, and an associate professor in the Department of Molecular and Medical Genetics at the University of Toronto.
"At first we were astonished and didn't believe our results because for years we had been taught that most variation in DNA was limited to very small changes. Then we heard the Harvard group was making similar observations and ultimately we combined our data and came to the same conclusion," added Dr. Scherer.
Early information from the Human Genome Project indicated that the DNA in the genome of any two individuals is 99.9 per cent identical with the 0.1 per cent variation arising primarily from some three million single nucleotide changes scattered amongst the chromosomes. The new data from the Sick Kids and Harvard groups revealed 255 regions (comprising more than 0.1 per cent) of the genome where large chunks of DNA are present in different copy numbers between individuals. Over 50 per cent of these alterations lead to changes in gene numbers and at least 14 regions overlapped with known sites associated with human disease.
Since discoveries of genetic differences between humans of this order of magnitude are being found at this stage in the game any estimates about which genetic variations are most responsible for making us different from other primates should be seen as tentative guesses at this point. Those estimates may be based on false assumptions about how many and what kinds of genetic variations any two species have. There may be yet more genetic variations waiting to be discovered and some of the regions now thought to contain junk DNA may be serving some as-yet-undiscovered regulatory purposes.
By examining dental information derived from molar wear patterns a pair of anthropologists has been able to show that human life expectancy increased during the Upper Paleolithic Period.
ANN ARBOR, Mich.---Researchers at the University of Michigan and the University of California at Riverside have discovered a dramatic increase in human longevity that took place during the early Upper Paleolithic Period, around 30,000 B.C.
In their study of more than 750 fossils to be published July 5 in the Proceedings of the National Academy of Sciences, anthropologists Rachel Caspari and Sang-Hee Lee found a dramatic increase in longevity among modern humans during that time: the number of people surviving to an older age more than quadrupled.
By calculating the ratio of old-to-young individuals in the samples from each time period, the researchers found a trend of increased survivorship of older adults throughout human evolution. It's not just how long people live that's important for evolution, but the number of people who live to be old, Caspari and Lee pointed out.
The increase in longevity that occurred during the Upper Paleolithic period among modern humans was dramatically larger than the increase identified during earlier periods, they found. "We believe this trend contributed importantly to population expansions and cultural innovations that are associated with modernity," they wrote.
A large number of older people allowed early modern humans to accumulate more information and to transmit specialized knowledge from one generation to another, they speculated. Increased adult survivorship also strengthened social relationships and kinship bonds, as grandparents survived to educate and contribute to extended families and others. Increased survivorship also promoted population growth, the authors explain, since people living longer are likely to have more children themselves, and since they also make major contributions to the reproductive success of their offspring.
"Significant longevity came late in human evolution and its advantages must have compensated somehow for the disabilities and diseases of older age, when gene expressions uncommon in younger adults become more frequent," the authors noted.
"There has been a lot of speculation about what gave modern humans their evolutionary advantage," Caspari said. "This research provides a simple explanation for which there is now concrete evidence: modern humans were older and wiser."
Here is my FuturePundit speculation on this report: the lengthening of lifespans created a selective pressure for higher intelligence. When people started living longer they accumulated more knowledge. The increase in available knowledge increased the value of having a high cognitive ability to sort through, analyze, and apply that knowledge. A smarter person can notice more and learn more useful lessons from an accumulation of life experiences than can a less intelligent person. So genetic mutations that lengthened lifespans may have led to selection for mutations that increased intelligence. Then the selection for higher intelligence likely increased the value of living even longer which would have fed back into selecting for longer lifespans.
But important questions remain unanswered: Did any Upper Paleolithic civilizations collapse from spiralling taxes enacted in a futile attempt to meet unfunded pension liabilities? Were massive human migrations across the continents driven by a desire to escape from old age pension taxes?
They judged the age of specimens by examining wear to teeth and classified "old" as twice the age of sexual maturity - roughly 30 years.
Sociologists Satoshi Kanazawa and Mary Still have found that teaching young women makes male teachers less satisfied with their wives.
Kanazawa believes that young female students are a vocational hazard for both male teachers and university lecturers. In a study he conducted on the marital status of Americans, Kanazawa found that male secondary school teachers and university lecturers were far more likely to be divorced than men in other professions.
Being surrounded by young and beautiful women caused the teachers to become dissatisfied with their wives and this often resulted in marriage breakdown.
At the time of the investigation, Kanazawa was lecturing at the geographically confusing Indiana University of Pennsylvania in America. Collaborating with fellow sociologist Dr Mary Still, of Cornell University, he discovered that teachers who had continuous exposure to pretty young female students found women in their own age group less attractive. The researchers describe the psychological process as "contrast and comparison effects".
All things thus considered, their models could predict divorce status 86 percent of the time. The bottom line: with the GSS as background, and controlling for other factors, the study shows that male secondary school teachers or college professors are nearly 80 percent more likely to be divorced than men in other professions.
There is accumulating evidence (see below) that television, movies, and still pictures are exerting a similar effect. The more one has to compare to the more likely that achievable choices will seem less satisfying. There is a general trend toward a greater ability to compare due to urbanization, advances in communications, advances in transportation, and changing work place practices. All these changes must be making marriage less likely to be entered into and less likely to last.
In a seminal 1970s study, psychologist Douglas Kenrick barged in on male students whilst they were watching the ‘babe’-packed TV programme Charlie’s Angels, and asked them to rate the attractiveness of a picture of an average female student. For comparison, he did the same with students watching largely ‘babe’-free shows, like the news.
He found that the men watching Charlie’s Angels gave the average female student a lower score than the news-watchers. In further experiments, he showed slides to three groups of male students, respectively of Playboy centrefolds, averagely-attractive women and abstract art. Sure enough, the Playboy group rated an average-looking woman lower than the others. This effect transferred to real life. After watching the slides, the Playboy centrefold-affected group rated their actual girlfriends lowest, not only in terms of attractiveness, but in how much they loved them.
To top it all, Kenrick showed male and female students slides of models and of average people. For both sexes, exposure to models of their own sex resulted in a lowering of mood, whereas seeing stunners of the opposite sex either raised their spirits or had no effect. Many other studies have produced similar results.
The strange thing is, being bombarded with visions of beautiful women (or for women, socially powerful men) doesn't make us think our partners are less physically attractive. It doesn't change our perception of our partner. Instead, by some sleight of mind, it distorts our idea of the pool of possibilities.
These images make us think there's a huge field of alternatives. It changes our estimate of the number of people who are available to us as potential mates. In changing our sense of the possibilities, it prods us to believe we could always do better, keeping us continually unsatisfied.
"The perception of the comparison pool is changed," says Gutierres. "In this context our partner doesn't look so great." Adds Kenrick: "You think, `Yes, my partner's fine--but why do I have to settle for fine when there are just so many great people out there?'" All you have to do is turn on the TV or look at the covers of magazines in the supermarket checkout line to be convinced there are any number of incredibly beautiful women available.
How is this changing the selective pressures on the human species? Are the least attractive people so repelled by other unattractive people that less attractive people are actually far less likely to reproduce now than they were in the past? Is beauty therefore being selected for? Or are the least attractive so resigned to their lack of attractiveness that they are more willing to hook up with a less attractive mate and stay together aware of their lack of real alternatives?
There is another possibility: The most attractive could have so many more choices now that high status attractive men may be spending less of their lives married and may be having fewer offspring. Both the greater intellectual ability that boosts their status and their greater physical attractiveness may be getting selected against.
A study of Swedish workplaces by sociologist Yvonne Åberg found that simple proximity to the opposite sex in the workplace boosted divorce rates considerably.
The seven-year study of 37,000 employees at 1,500 workplaces provides empirical evidence that working with people of the opposite sex is hazardous to your marriage. Working with co-workers who are all of the opposite sex increases the divorce rate by a startling 70%, compared with an office filled with co-workers of the same sex. Whether the co-workers were single or married had no impact, says author Yvonne Aberg, now a research fellow at Nuffield College, Oxford University, England.
All these reports are signs that natural selection is operating in different ways than it has in the past. Selective pressures for mating have changed and continue to change as living standards rise and technology changes how society is structured. What is less obvious is just which characteristics are being selected for and against.
In the longer run other technological trends are going to change the pressures caused by comparisons to attractive people.
Some of these responses may seem like they will ameliorate the problem of dissatisfaction over comparisons. Certainly male attraction to women in their late teens and early twenties will become easier to satisfy when rejuvenation therapies allow everyone to become young again. What many women claim to see as a shallow aspect of male nature is actually going to become a fairly easy problem to fix once all females can look young and attractive. But female desires for males of high status will be much harder to satisfy with a technological fix since in order to have some men with high status other men must be of lower status. We do not live in Lake Woebegone where all children are above average or all men are of high status.
There is also a political dimension in the trend toward greater ability to compare. While men are comparing their female mates to other women and they are also comparing themselves to other men in competition for those women the comparisons do not end there. More worrisome are politically charged comparisons across national borders and between ethnic, religious, and other groups. See my ParaPundit post Competition, Resentment, Demotivation, And Large Status Hierarchies. I see this as a real and growing problem in both domestic and international politics and terrorism as partially due to this phenomenon.
Satoshi Kanazawa of the London School of Economics and his colleague, Jody L. Kovar, assert that beautiful people also tend to be smart people -- and vice versa.
In the July issue of Intelligence, the sociologists offer a theory to explain the confluence of beauty and brains. Their argument, in a nutshell: Intelligent men achieve higher status and marry beautiful women, who pass their genes on to their disproportionately attractive and smart kids, who win mates who are good-looking or brainy, and so on. Or at least that's what they put forth in the journal article, "Why Beautiful People are More Intelligent."
Click through and read the evidence. Their argument seems very likely to be correct. Of course, this also means that there is a flip side of dummy-ugly hybrids being bred as well.
Unfortunately, there is some pretty strong evidence that at least in Western societies intelligence currently is being selected against. This does not bode well for the future of either intelligence or natural beauty. If the brains are hooking up with the beauties and not having many kids then successive generations will be dumber and uglier.
If you are looking for some ray of hope in current human evolutionary trends there is one factor I've yet to see accounted for in any study on reproduction and intelligence: are smarter and higher class men more likely to divorce and remarry and have kids by their second spouse? My guess is that they are and that this effect will promote the spread of higher IQ genetic variations. But how big is that effect as compared to the glaringly obvious and quite strong phenomenon of people having fewer kids the more education they receive?
There is another interesting twist to the currently active selective pressures on human evolution in Western societies that I've yet to see discussed anywhere: Since people who have post-graduate degrees are politically more left-wing than people who have only bachelors degrees and since the more education one has the less likely one is to have kids (see the previous link) then are the genetic variations that code for a predisposition to left-liberalism being selected against? My guess is that high IQ people who do not go on to grad school are politically to the right of high IQ people who do. Well, the latter are probably having fewer kids than the smarties who do not go to grad school. So are the future generations of high IQ people going to be more right-wing than they are now?
In the longer run genetic engineering of offspring will be used to make offspring both better looking and smarter and likely more out-going and charming as well. What is less obvious to me is what their politics will be like. Once offspring genetic engineering becomes possible will people tend to choose personality characteristics for their children that make them crunchy granola liberals, paleoconservatives, highly individualistic libertarians, or what exactly? My one guess along these lines is that there will be a polarization with people choosing personality characteristics for their offspring that are stronger versions of various personality types.
Scientists studying the elusive western gorilla observed that neighboring social groups have surprisingly peaceful interactions, in contrast to the aggressive male behavior well documented in mountain gorillas. By analyzing the DNA from fecal and hair samples of the western gorilla, scientists uncovered evidence that these neighboring social groups are often led by genetically related males. These findings suggest connections between genetic relationships and group interactions, parallels with human social and behavioral structures, and clues to the social world of early humans.
In the new work, reported by Brenda Bradley and colleagues at the Max Planck Institute for Evolutionary Anthropology and Stony Brook University, the researchers collected DNA samples to characterize patterns of paternity within and among western gorilla social groups. The authors found that a strong majority of silverbacks were related to other silverbacks in the area and that in almost all cases, the nest sites of related silverbacks were found near each other. It was already known that both male and female western gorillas leave their natal group once mature, but the new findings suggest that the dispersing males may remain in the vicinity of male kin, forming a so-called "dispersed male network."
It makes sense that selective pressures would favor a greater willingness to harm those more genetically distant. Closer relations share more DNA in common and therefore their well-being and reproductive success is more in the interest of their close relatives than is the case with more distant members of the same species.
The researchers theorize that the dispersed male network and the social behavior of the western gorilla may be connected, in part because peaceful interactions between related males may be beneficial. This idea is in keeping with kin-selection theory, a well-regarded set of ideas for how related members of a society interact to benefit the related group. According to the authors, western gorilla male networks may benefit younger males as they attempt to attract females and form new groups, since male-male aggression is thought to hinder the acquisition and retention of females. Similar scenarios have been reported for some bird species, and there is ample evidence of such relationships underlying aspects of human social interactions, including marriage patterns. In addition, some relevant aspects of western gorilla society are shared with chimpanzees. The new findings point to characteristics that appear to be held in common between humans and some other African apes, suggesting that kinship patterns both within and among groups may have played an important role in shaping the social world of early humans.
I'll bet that humans will eventually be found to have genetic variations that encourage this sort difference in behavior as well.
"In primates, having a bigger brain means you have a disproportionately larger frontal cortex," said Eliot Bush, a PhD candidate at Caltech who worked on the study.
PASADENA, Calif.--Everybody from the Tarzan fan to the evolutionary biologist knows that our human brain is more like a chimpanzee's than a dog's. But is our brain also more like a tiny lemur's than a lion's?
In one previously unsuspected way, the answer is yes, according to neuroscientists at the California Institute of Technology. In the current issue of the Proceedings of the National Academy of Sciences (PNAS), graduate student Eliot Bush and his professor, John Allman, report their discovery of a basic difference between the brains of all primates, from lemurs to humans, and all the flesh-eating carnivores, such as lions and tigers and bears.
The difference lies in the way the percentage of frontal cortex mass increases as the species gets larger. The frontal cortex is the portion of brain just behind the forehead that has long been associated with reasoning and other "executive" functions. In carnivores, the frontal cortex becomes proportionately larger as the entire cortex of the individual species increases in size--in other words, a lion that has a cortex twice the size of another carnivore's also has a frontal cortex twice the size.
By contrast, primates like humans and apes tend to have a frontal cortex that gets disproportionately larger as the overall cortex increases in size. This phenomenon is known as "hyperscaling," according to Bush, the lead author of the journal article.
What this says about the human relationship to the tiny lemurs of Madagascar is that the two species likely share a developmental or structural quirk, along with all the other primates, that is absent in all the carnivores, Bush explains. "The fact that humans have a large frontal cortex doesn't necessarily mean that they are special; relatively large frontal lobes have developed independently in aye-ayes among the lemurs and spider monkeys among the New World monkeys."
The hyperscaling mechanism is genetic, and was presumably present when the primates first evolved. "Furthermore, it is probably peculiar to primates," says Allman, who is Hixon Professor of Neurobiology at Caltech.
Given that brain size differs between humans it would be interesting to know whether this same mathematical relationship exists when comparing humans with each other/.
Primate frontal cortex hyperscales relative to the rest of neocortex and the rest of the brain. The slope of frontal cortex contrasts on rest of cortex contrasts is 1.18 (95% confidence interval, 1.06-1.30) for primates, which is significantly greater than isometric. It is also significantly greater than the carnivore value of 0.94 (95% confidence interval, 0.82-1.07). This finding supports the idea that there are substantial differences in frontal cortex structure and development between the two groups.
Whatever may have been the cause of this hyperscaling? Is there a reason why the way all primates function causes this to be advantageous?
The researchers looked at 2,800 women living in two 18th and 19th century farming communities in Finland and Canada.
They wanted to see how long women lived after their menopause and what effect that might have on how many babies their own children had.
The data showed women had two extra grandchildren for each extra decade they lived after 50.
The grandmothers not only increased the number of children their children had but also increased the number that survived childhood.
The research, led by Mirkka Lahdenpera, a professor of human ecology at the University of Turku in Turku, Finland, found that "prolonged post-reproductive longevity in humans is associated with greater grandchild production."
In both Canada and Finland, women gained two extra grandchildren for every decade they lived beyond age 50.
The research also reveals that the declining role of grandmothers in childrearing is one factor among many that have led to the birth rate falling in modern societies.
Because of greater mobility people are less likely to live next to their parents. Therefore they are less likely to have parental babysitting services available.It would be interesting to look at industrial society populations today and measure physical distance between parents and their children and compare that to the number of offspring the children have. In light of this study it seems likely that people who do not live near their mothers have smaller families than those who do.
The effect of living near one's mother might not be as strong on childbearing today for the upper classes in particular since wealthy people can afford nannies and babysitters.
The post-reproductive survival of humans—women in particular—is truly unusual. Non-reproductive “helpers” of individuals who are breeding are found in many species. But they are usually young animals that have yet to establish themselves, rather than relics from previous generations. The post-reproductive elderly just die. Chimpanzees, for example, have a similar pattern of fertility to people. A female chimp's fertility peaks in her late 20s, and is more or less extinguished by her mid-40s. But in chimpanzees, mortality rises as fertility declines.
A previous FuturePundit post reported on the work of Bruce Lahn at the University of Chicago in exploring the evolution of the Abnormal Spindle-Like Microcephaly Associated (ASPM) gene. Mutations in ASPM have played a key role in causing the evolutionary lineage leading up to modern humans to develop bigger and smarter brains. Well, a recent report on Lahn's work that covers much the same ground but ends with a very intriguing mention of Lahn's next step: insertion of the human ASPM gene into mice.
In future experiments, Lahn will insert the human ASPM gene into mice to see what affect it has on brain development. He hopes to reconstruct the detailed story of how the human brain grew and changed as the result of natural selection, thereby creating the thing that makes us each unique—the human mind.
The creation of transgenic mice using a human gene which plays a role in determining brain could potentially produce a larger brained and smarter mouse. That outcome is by no means assured. Yet this real-life experiment brings to mind David Brin's Uplift Saga series of books including Sundiver, the Hugo and Nebula award winning Startide Rising, and The Uplift War. The term "uplift" in this context refers to the lifting up of less intelligent species to a level of sentience similar to that of humans. In Brin's saga humanity has used genetic engineering to uplift both chimpanzees and dolphins into human-like sentience.
It seems inevitable (barring the extinction of the human race in the next few decades) that the knowledge will be found for how to genetically engineer human-level intelligence into other species. At the same time, the knowledge will also be found for how to genetically engineer humans to be much smarter. Once DNA sequencing becomes cheap enough just the ability to compare the DNA sequences of humans of different levels of intelligence will lead to the discovery of many variations that will allow the average level of intelligence to be boosted quite dramatically. Building on that knowledge will be possible to discover variations that have not yet happened in humans that will allow an even greater boosting of human intelligence to levels not seen in any humans to date.
One danger of uplifting other species is that they may not feel any loyalty or empathy to humans. We may just create competitors who will clash with us in ways that make conflicts between human groups seem tame by comparison. In light of this threat an argument can be made for the idea that uplifting dogs will pose less of a threat to humans than uplifting various primates. Dogs have been bred for tens of thousands of years to form bonds with humans and to feel protective toward humans. It will also eventually be possible to genetically engineer this form of loyalty and empathy toward humans into other uplifted species. But with dogs we will be able to start with a species that already possesses some of the desired qualities that would reduce the danger that another sentient species would become a threat to humans.
A chimpanzee enters a room where food is hidden in one of two opaque containers. A human gazes at the container that hides the food. Reaches for it with outstretched arm. Marks the container with a wooden block. The chimp doesn't get the message, even though chimpanzees are one of Homo sapiens' two closest extant primate relatives and might be expected to figure it out. Biological anthropologist Brian Hare and colleagues tried this game with 11 chimps, and only two of the brainy apes used the conspicuous cues to find the food.
Dog owners may not be surprised to learn that nine of 11 dogs in the same situation correctly read the human signals and found the food. A control exercise established that odor was not a cue in either trial.
"Our new work provides direct evidence that dogs' lengthy contact with humans has served as a selection factor, leading to distinct evolutionary changes," says Hare, who recently completed his Ph.D. in anthropology in Harvard's Faculty of Arts and Sciences. "This is the first demonstration that humans play an ongoing role in the evolution of canine cognition."
Ádám Miklósi led a group of researchers at Eötvös University in Budapest, Hungary who conducted the "shell game" tests on wolves. The test wolves were raised by humans and socialized to a comparable level as their dog counterparts. But although they could follow some signals, the wolves could not perform to the level of dogs.
Miklósi's test also included an important second step. He presented the animals with an unsolvable problem—a bowl of food that was impossible to access. The team found that while wolves continued to work at the unsolvable problem for long periods, dogs quickly looked at the humans for help.
Dec. 4 — The Eves of the dog world are five or six wolf females that lived in or near China nearly 15,000 years ago, according to a series of genetic research.
The researchers believe that by 10,000 to 12,000 years later, 10 "progenitor breeds" of dog had been created to fulfill different roles alongside their masters. It took a further 5000 to 3000 years for people to create the 300 or so pure breeds known today.
What is interesting about this result from a human evolutionary perspective is that it demonstrates how, contrary to popular belief, 10,000 or 20,000 years of selective pressure from relatively new environmental factors can produce large changes in shape, cognitive function, and behavior of a species. The example of dogs changing so much under human influence suggests the possibility that humans have changed a great deal as they moved out of Africa and evolved to fit into various ecological niches around the world.
An example of an evolutionary adaptation in humans that may have developed as recently as dogs developed from wolves occurred in the human Andean population which developed an adaptation to high altitudes.
Previous studies have shown that the Tibetan, Ethiopian and Andean populations have developed slightly different ways of boosting their oxygen levels to cope with the thin air. Those in the Andes pump out more haemoglobin - a molecule that carries oxygen around in the blood. The Tibetans, by contrast, have relatively low haemoglobin levels but breathe faster to take in more oxygen. "The slightest bit of exercise makes them really pant," Beall says.
The Tibetans probably had more time in which to develop high altitude adaptations and certainly the Ethiopians had more time since humans have been in Africa for a longer period of time. But the Andean human adaptation couldn't begin until the human populations came across the Bering Strait and then migrated all the way to South America.
Loren Cordain claims that the ability of adult northern Europeans to digest lactose sugar is a fairly recent adaptation that may have become widespread in just the last few hundred generations of humans.
Commentary: There are calculations which estimate how long it took to increase the gene for adult lactase persistence (ALP) in northern Europeans from a pre-agricultural incidence rate of 5% to its present rate of approximately 70% [Aoki 1991]. (Note: The enzyme lactase is required to digest the sugar lactose in milk, and normally is not produced in significant quantity in human beings after weaning.) In order for the gene frequency to increase from 0.05 to 0.70 within the 250 generations which have occurred since the advent of dairying, a selective advantage in excess of 5% may have been required [Aoki 1991].
Therefore, some genetic changes can occur quite rapidly, particularly in polymorphic genes (those with more than one variant of the gene already in existence) with wide variability in their phenotypic expression. ("Phenotypic expression" means the physical characteristic(s) which a gene produces.) Because humans normally maintain lactase activity in their guts until weaning (approximately 4 years of age in modern-day hunter-gatherers), the type of genetic change (neoteny) required for adult lactase maintenance can occur quite rapidly if there is sufficient selective pressure. Maintenance of childlike genetic characteristics (neoteny) is what occurred with the geologically rapid domestication of the dog during the late Pleistocene and Mesolithic [Budiansky 1992].
Influence of human culture on genetic selection pressures. However--and this is where it gets interesting--those population groups that do retain the ability to produce lactase and digest milk into adulthood are those descended from the very people who first began domesticating animals for milking during the Neolithic period several thousand years ago. (The earliest milking populations in Europe, Asia, and Africa began the practice probably around 4,000 B.C.) And even more interestingly, in population groups where cultural changes have created "selection pressure" for adapting to certain behavior--such as drinking milk in this case--the rate of genetic adaptation to such changes significantly increases. In this case, the time span for widespread prevalence of the gene for lactose tolerance within milking population groups has been estimated at approximately 1,150 years--a very short span of time in evolutionary terms.
It is worth noting that domestication of milk animals was such a large selective advantage that it could cause the mutation for lactase expression in adults to be selected for in a relatively short period of time. But since the selective pressure for adult lactase expression was very strong this suggests than any kind of behavior or other aspect of human physiology that was beneficial for doing milk animal herding and protection of milk animals would also have been selected for very strongly at the same time that adult lactase expression was being selected for. We have to consider the possibility that personality types more suited for the herding-tending and herd-protection may have been fundamentally different than the personality types most suited for a hunter-gatherer lifestyle that involved no use of milk animals.
Another post-Africa adaptation in humans is the spread of a mitochondrial mutation for generating more heat in colder weather.
These lineages are not found at all in Africans but occur in 14 percent of people in temperate zones and in 75 percent of those inhabiting Arctic zones. Wallace and his colleagues say this correlation is evidence that the lineages were positively selected because they help the body generate more heat.
Wallace says that climatic selection may have operated on the human population from the moment it moved north of the African tropics. Most such pioneers died but two lineages, known as M and N, arose in northeast Africa some 65,000 years ago and might have been adapted to temperate climates. Almost everyone outside of sub-Saharan Africa has mitochondria descended from the M and N lineages.
The writers of the research paper reporting on the heat-generating mtDNA variation speculate that human mtDNA has adaptations for local environmental conditions that are making humans have higher incidences of a number of diseases due to modern environments and diets.
Evidence has already accumulated that different human mtDNA lineages are functionally different. Haplogroup T is associated with reduced sperm motility in European males (30), and the tRNAGln nucleotide position 4336 variant in haplogroup H is associated with late-onset Alzheimer's disease (31). Moreover, Europeans harboring the mild ND6 nucleotide position 14484 and ND4L nucleotide position 10663 Leber's hereditary optic neuropathy missense mutations are more prone to blindness if they also harbor the mtDNA haplogroup J (32, 33), and haplogroup J is associated with increased European longevity (34). Because haplogroup J mtDNAs harbor two missense mutations in complex I genes (Y304H in ND1 and A458T in ND5), in addition to the above-mentioned L236T variant in the cytb gene, these polymorphisms all could affect the efficiency of OXPHOS ATP production and thus exacerbate the energy defects of mildly deleterious new mutations.
Given that mtDNA lineages are functionally different, it follows that the same variants that are advantageous in one climatic and dietary environment might be maladaptive when these individuals are placed in a different environment. Hence, ancient regionally beneficial mtDNA variants could be contributing to modern bioenergetic disorders such as obesity, diabetes, hypertension, cardiovascular disease, and neurodegenerative diseases as people move to new regions and adopt new lifestyles.
In humans mitochondrial DNA (mtDNA) is only 16,569 DNA letters long whereas the DNA in the human cell nucleus is over 3 billion letters long. Note that while the mtDNA is very small it still manages to have many variations with different effects on disease risks and environmental adaptation. It seems likely that the mtDNA heat variation is not the only mtDNA variation is a result of selective pressures to allow humans to adapt better to local conditions.
Another important thing to note about canine evolution is that to the extent that dog breeds developed special adaptations to perform various functions those dogs reduced the need for humans to do those functions and hence changed the selective pressure on humans.
"We know that dogs were useful for lots of things in Stone Age culture, as draft animals, in hunting, for warmth, and for protection," said Jennifer Leonard, a postdoctoral fellow at the Smithsonian Institution’s National Museum of Natural History. And in sharing food, shelter, survival and play, modem dogs have somehow genetically acquired an insight about humans that has earned them the title of man's best friend
For instance, a hunting dog that could smell prey reduced the need for humans to have an acute sense of smell for that purpose. Therefore the domestication of dogs must have changed the selective pressures on humans. Those changes in selective pressures must have been different depending on the types of dogs and the ecological niches various human groups found themselves in. Human groups that learned to train and work with dogs for various purposes had a selective advantage against human groups that did not do so. So just as humans have exerted selective pressures in dog evolution it seems highly likely that dogs have caused selective pressures in human evolution.
The researchers, led by Howard Hughes Medical Institute (HHMI) investigator Bruce Lahn at the University of Chicago, reported their findings in an advance access article published on January 13, 2004, in the journal Human Molecular Genetics. Patrick Evans and Jeffrey Anderson in Lahn's laboratory were joint lead authors of the article.
“People have studied the evolution of the brain for a long time, but they have traditionally focused on the comparative anatomy and physiology of brain evolution,” said Lahn. “I would venture, however, that there really hasn't been any convincing evidence until now of any gene whose changes might have contributed to the evolution of the brain.”
In this study, the researchers focused on a gene called the Abnormal Spindle-Like Microcephaly Associated (ASPM) gene. Loss of function of the ASPM gene is linked to human microcephaly - a severe reduction in the size of the cerebral cortex, the part of the brain responsible for planning, abstract reasoning and other higher brain function. The discovery of this association by HHMI investigator Christopher A. Walsh and colleagues at Beth Israel Deaconess Medical Center is what prompted Lahn to launch an evolutionary study of the gene.
Lahn and his colleagues compared the sequence of the human ASPM gene to that from six other primate species shown genetically to represent key positions in the evolutionary hierarchy leading to Homo sapiens. Those species were chimpanzee, gorilla, orangutan, gibbon, macaque and owl monkey.
“We chose these species because they were progressively more closely related to humans,” said Lahn. “For example, the closest relatives to humans are chimpanzees, the next closest are gorillas, and the rest go down the ladder to the most primitive.”
For each species, the researchers identified changes in the ASPM gene that altered the structure of the resulting protein, as well as those that did not affect protein structure. Only those genetic changes that alter protein structure are likely to be subject to evolutionary pressure, Lahn said. Changes in the gene that do not alter the protein indicate the overall mutation rate - the background of random mutations from which evolutionary changes arise. Thus, the ratio of the two types of changes gives a measure of the evolution of the gene under the pressure of natural selection.
Lahn and his colleagues found that the ASPM gene showed clear evidence of changes accelerated by evolutionary pressure in the lineage leading to humans, and the acceleration is most prominent in recent human evolution after humans parted way from chimpanzees.
“In our work, we have looked at evolution of a large number of genes, and in the vast number of cases, we see only weak signatures of adaptive changes,” said Lahn. “So, I was quite surprised to see that this one gene shows such strong and unambiguous signatures of adaptive evolution — more so than most other genes we've studied.”
By contrast, the researchers' analyses of the ASPM gene in the more primitive monkeys and in cows, sheep, cats, dogs, mice and rats, showed no accelerated evolutionary change. “The fact that we see this accelerated evolution of ASPM specifically in the primate lineage leading to humans, and not in these other mammals, makes a good case that the human lineage is special,” said Lahn.
According to Lahn, among the next steps in his research will be to understand how ASPM functions in the brain. Studies by Walsh and others hint that the protein produced by the gene might regulate the number of neurons produced by cell division in the cerebral cortex. Lahn and his colleagues plan functional comparisons of the ASPM protein among different species, to understand how this gene's function or regulation changes with evolution.
The acceleration of ASPM functional changes in the whole lineage this suggests that there was evolutionary selective pressure for changes in cognitive function not just from the point where humans split off from chimpanzees but even much early as well. Was that pressure consistent and continuing? Or did it happen periodically? One can only speculate at this point. Perhaps something about the shape of a primate makes higher intelligence more useful. If so then the more that shape changes in certain directions the more the selective pressure increases. That could come as a result of the types of habitats primates moved into or how they functioned in those habitats or from what they used as food sources or still other factors. There are a lot of possibilities.
One thing interesting about intelligence as an adaptive mutation is that it allows an animal to learn how to adapt itself to new environments. An animal that is in exactly the same environment that its ancestors evolved in might be able to do well in that environment just by following instincts. But in a new environment a species has to either get mutated into a new shape that better adapts the species to the environment or it has to learn how to function in that environment without changing shape. Look at human clothing. A species with fur that migrates into a colder environment might simply gradually develop metabolic changes for cold weather and fur thickness changes that adapt that species to the colder environment. Humans whose ancestors lived in colder environments do have genetic variations in their mitochondria that allow them to be warmer in cold weather. But humans also were smart enough to develop the ability to kill furry animals and use their pelts for clothing to be warmer. So humans could use their intelligence to adapt themselves to cold climates more rapidly than specific mutational changes would happen to help in the adaptation. Humans spread out across all the continents and adapted themselves to a very wide range of environments even before the modern age of science and technology. What will be interesting to find out is whether specific types of ancient environments required greater cognitive abilities and, if so, what was it about those environments that levelled greater demands on the brain.
You might be wondering how exactly scientists can detect selective pressure on a gene. Note how the article talks about mutations that are not functionally significant versus mutations that are functionally significant. Well, compare two related species for the ratio of functionally significant to functionally insignificant variations in the same gene. The higher the ratio the higher the selective pressure must have been.
Here's an intuitive example of why ratios of functionally signficant to functionally insignificant mutations reveal the extent of past selective pressure: Suppose at some point in the past there was a species that has only a million animals of that species. Suppose they had some gene we will call X. Suppose they all had only functionally insignificant mutations in X and that between the million animals of that species they had 20 different combinations of mutations in X. Then suppose a single animal in that species was born that had a mutation in X that caused a functional change that made that animal more adaptive. Perhaps the mutation in X made the animal smarter and therefore more successful in finding food. Well, that animal with the "smart X" variation also had one of the existing 20 combinations of functionally insignificant mutations. The other 19 combinations existed only in animals that did not have the "smart X" intelligence-enhancing mutation. All the other animals of that species will therefore be less successful, on average, at reproducing. That will, over a period of generations, cause those other 19 combinations in the X gene to become far less common. Many of the combinations in X likely will disappear entirely as their carriers become outcompeted in the search for food and fail to reproduce successfully. The 1 combination of insignificant variations that occurs with the "smart X" mutation will become far more common and may become the only combination of insignificant variations in the X gene until new insignificant combinations start accumulating across generations as new mutations happen in animals that have the "smart X" mutation.
The point is that a valuable mutation will mprove the relative reproductive success of the first animal that gets it. But then any unimportant or less important mutations that animal also has will be propagated along with the important mutation. The amount of overall variation in that gene will go down in future generations as the animals that do not have the valuable mutation but which have various functionally insignificant mutations do not reproduce as successfully. Valuable mutations have the effect of reducing the number of functionally unimportant mutational variations that will be found around genes that has the valuable mutations.
Update: Nicholas Wade of the New York Times has more details about the historical frequency of ASPM mutations.
"There has been a sweep every 300,000 to 400,000 years, with the last sweep occurring between 200,000 and 500,000 years ago," Dr. Lahn said, referring to a genetic change so advantageous that it sweeps through a population, endowing everyone with the same improved version of a gene.
By this measure humans may be due for another ASPM mutation. Perhaps there is some human out there walking around with the next intelligence-enhancing ASPM mutation.
Where Lahn talks about a mutation that "sweeps through a population" understand what that really means: All animals that did not have the mutation in a given species were outcompeted and, over some generations, failed to reproduce. The mutation didn't just jump from one ape to another ape like a viral infection. The line of successive mutations were each so helpful for enhancing survival and reproduction that animals that didn't have them were outcompeted for food or for mates or in fights and perhaps in all of those ways.
Wade says at least 5 other genes cause microcephaly but they have not yet been identified. Once they are expect evolutionary geneticists to repeat the same comparison between species as was done with ASPM. While few humans appear to have functional variations in ASPM (aside from victims of microcephaly) it is possible that some of these yet-to-be-discovered genes will turn out to vary between humans. Humans do vary in brain size and brain shape. Genetic variations in some genes must be causing this. Though some of those variations might be occurring in genes that are not responsible for microcephaly.
Nicholas Wade of the New York Times has written an excellent article reviewing what is known about chimpanzee behavior and differences and similarities with human behavior. For instance, chimps are very territorial and patrol borders in order to maintain large territorial areas for gathering fruit.
In two known cases, a chimp community has wiped out all of a neighbor's males. Though the females may be absorbed into the victors' community, the basic goal seems to be getting rid of a rival rather than capturing females, since male chimps often attack strange females.
Within a community, there is a male hierarchy that is subject to what primatologists euphemistically call elections. Alpha males can lose elections when other males form alliances against them. Losing an election is a bad idea. The deposed male sometimes ends up with personal pieces torn off him and is left to die of his wounds.
But the bonobos may hold more appeal for the most militant feminists.
An intriguing variation on the chimpanzee social system is that of bonobos, which split from chimps some 1.8 million years ago. With bonobos, who live in Congo south of the Congo River, the female hierarchy is dominant to that of males, and males do not patrol the borders to kill neighbors. Though bonobos are almost as aggressive as chimps, they have developed a potent reconciliation technique — the use of sex on any and all occasions, between all ages and sexes, to abate tension and make nice.
Anyone else flash on the 1960s hippie slogan "Make love, not war"?
Stand back far enough and forget for a moment that humans are so much smarter and capable of developing very complex technologies and of discovering scientific laws. Just look at human social forms. They seem similar to those of other primates. At the same time it seems conceivable that a different sentient species could naturally favor very different structures of relationships than what humans form. It seems likely that a substantial portion of how humans organize into groups has a genetic basis.
When it becomes possible to genetically engineer human personality characteristics and behavioral tendencies different groups of humans may choose to engineer their children to be as different from each other in social behevior as are bonobos and chimpanzees. Such engineered splits in the human race may lead to wars between groups. Disagreements about values that are genetically engineered to be radically different will not be easily resolved by negotiation.
Wade's mention of elections to throw out an alpha male reminds me of Paul H. Rubin's argument that reverse dominance hierarchies from the Pleistocene era serve as the impetus for creating democracy. It could well be that the characteristic that has led to the drive for democracy can be traced all the way back to before humans and chimpanzees split off from each other about one and a half million years ago. See the post: Human Desire For Freedom Evolved Before We Lived In Cities
Denis Dutton has written a review for Arts & Letters Daily of Emory University professor of economics and law Paul H. Rubin's book entitled Darwinian Politics: The Evolutionary Origin of Freedom
Rubin begins with that bracing idea that the often-coercive political control placed on human beings since the advent of cities is characteristic only of the Holocene. The human desire for freedom, he argues, is an older, deeper prehistoric adaptation: for most of their existence, human beings have experienced relative freedom from political coercion. Many readers will ﬁnd Rubin’s thesis counterintuitive: we tend to assume that political liberty is a recent development, having appeared for a while with the Greeks, only to be reborn in the eighteenth century, after millennia of despotisms, for the beneﬁt of the modern world. This is a false assumption, a bias produced by the fact that what we know best is recorded history, those 500 generations since the advent of cities and writing.
The fall from the proverbial garden of freedom began around ten thousand years ago at the beginning of the Holocene era when humans developed agriculture. With agriculture came the ability to maintain much more dense settlements and that, in turn, led to governments and the coercive power of governments to control people.
If this argument is correct (and I think it is) then the advent of dense settlements and coercive political systems must have created new selective pressures on genes that shape human personality and behavioral tendencies. Therefore people whose ancestors lived in denser communities for longer periods of time probably have different distributions of alleles for personality than people whose ancestors were more recently hunter-gatherers. We might expect, therefore, to find different average personality types in Mongolia than in the most densely populated regions of northern China. Also, we might expect to see different average personality types among the Hmong and other more remote groups in southeast Asia than among those living in the Mekong Delta.
Any area that has managed to maintain a strong administrative system of control for many generations almost certainly selected for different kinds of progeny. People more likely, due to temperament and behavior, to be killed or imprisoned by governments were less likely to reproduce. People who were adept at advancing thru the ranks of elaborate administrative systems (and China probably stands out in terms of sheer continued length of such systems) would have different personality types and would have been more likely to leave more progeny.
If the desire for freedom is a primitive Pleistocene urge and if city systems and larger empire administrative structures selected for different characteristics what does this hold for humanity's future? It is hard to say. Certainly, the innate desires to get along with large numbers of people and to submit to laws and norms of behavior are all useful. But there is a complex interaction between the many elements of human personality and once it becomes possible to control what personality characteristics offspring get it is hard to predict what humans will become like.
The Pleistocene era's selection for reverse dominance hierarchies probably provides the human mental characteristics that serve as the basis of democracy.
Rubin cites studies showing that hunter-gatherers had what are called “reverse dominance hierarchies,” where less dominate males acted individually or cooperated with each other to curtail the power of would-be dominants. Strategies for this would include “ridicule, refusal to obey commands, forcible resistance, and even homicide against those with too strong a desire for power.” A desire for freedom, then, for relative personal autonomy within the group, is a powerful Pleistocene adaptation pitted against extreme coercive hierarchy.
Imagine a country in which the government forces offspring to be born with less of the innate desire to form reverse dominance hierarchies. The result would be people who do not put up as much (or even any) resistance to the dictates of those in power. In anther country where people are free to choose the genetic characteristics of their offspring it is hard to predict what choices will be made and, as a consequence, what the resulting political system will look like.
Rubin sees both the impulse for support of the welfare state and the opposition to high taxes and the resentment toward freeloaders as all consequences of Pleistocene adaptations. Helping others in tough times might lead to their helping you out at a later point. At the same time. food was too scarce to tolerate freeloading. Rubin also argues that libertarianism is contrary to human nature and that humans want to meddle in each others' lives. Read the whole review. Very interesting.
One other point: My guess is that the distribution of alleles for the desire to be altruistic or to enforce rules or to force people not to be freeloaders will be found to be different in different parts of the political spectrum. A lot of political divisions will turn out to be, at least in part, due to average differences in personality characteristics that have their origins in the Pleistocene era. My bet is that once people start genetically tinkering with their offspring purer forms of socialists, libertarians, social conservatives, and other political types will be born and the political divisions within some societies and between societies will become greater as a result.
On Taiwan, abortions have skewed the island's demographics to the point that only two girls are born for every three boys.
An obvious consequence is that when the little king passes puberty, he discovers that the girl he liked in high school has gone to USC, probably never to return, while those who remain are being snapped up by other men.
To ease the gender gap, Taiwanese men import brides from the mainland. Unfortunately, these women are outnumbered by those smuggled into the country illegally, who, in exchange for $10,000, can legalize their status with marriages of convenience, then head for the brothels to earn real money. These bogus nuptials are difficult to detect since many Taiwanese men hop between marriages until they find a woman who can bear them a son.
The effect this will have is to select against the reproduction of economically less successful and physically less attractive males. Women prefer wealthier and higher status males and the approximately one third of Taiwanese males who are going to be left unable to reproduce will be, on average, lower status and less affluent. Any genetic variations that reduce economic success or physical attractiveness will therefore be selected against. This will probably tend to raise the average IQ of Taiwanese babies and probably will make them more driven and motivated. For more information on the practice of selective abortion of female fetuses in China and India see the post Girl Shortage Causes Wife Buying In India. While Nobelist Sydney Brenner sees natural selection as obsolete (see Sydney Brenner: Biological Evolution Is An Obsolete Technology) it seems obvious that natural selection is still happening to humans. The only thing that has changed is that different genes are being selected for or against than was previously the case before modern medicine and cheap foods became available.
Update: To clarify a point: It can be debated just what is natural versus artificial selection. What is artificial must somehow involve sentience modifying and creating elements of an environment. Should we limit the use of the term artificial selection to refer only to changes in offspring genes caused by conscious engineering of offspring? Or if we change our environments for other reasons and, as a side effect, cause those environments to exert different selective pressures on us that change the frequency of alleles in successive generations should we call that artificial selection too? Heck if I know. I care less about semantic debates than about understanding the actual processes that are at work.
One can (and some people do) even carve out something called sexual selection as distinct from natural selection (that strikes me as more of a subcategory of natural selection - not that I care all that much whether it is treated as a subcategory). But the important point here is that just because we have modified our own environment in substantial ways does not mean that the environment is not still exerting selective pressures on us.
Selection that causes different frequencies of alleles from one generation to the next is still happening. While there are some exceptions of rather limited scope (e.g. preimplantation testing of IVF embryos) we aren't yet using genetic engineering to customize our offspring. Yet for other reasons we have made many changes to our environments which, as a side effect, are causing changes in the frequency of many alleles in successive generations of humans. Scientists who claim that human evolution by natural selection has stopped are trying to imply that there are no selective pressures at work. But it is incredibly obvious that this is an erroneous conclusion.