January 14, 2004
Researchers Find Key Gene For Evolution Of Human Intelligence

Bruce Lahn and collaborators have discovered signs of strong selective pressure in primates on a gene that affects brain size.

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.

Share |      Randall Parker, 2004 January 14 12:29 AM  Trends, Human Evolution


Comments
Fly said at January 14, 2004 11:31 AM:

Intelligence and culture are co-evolving. Wolves learn to hunt as a pack. Increased intelligence leads to better individual success in the pack and better success for the pack as a whole. As the pack intelligence increases the wolf culture evolves. The combination is so powerful that once a threshold is reached intelligence becomes strongly selected.

Being bipedal with hands aided human tool development. The human vocal system aided language development. Tools and language made the intelligence-culture combo even more powerful. So intelligence-culture-language-tools all co-evolved. Changing and challenging environments accelerate this process as the combo allowed quick adaptation and exploitation of new ecological niches.

My guess is that there are genes strongly supporting these abilities that will show evidence of rapid genetic selection.

(A similar combo of forces is generating the incredible cultural development we are experiencing. Improved computers, communications, social organizations, science, scientific tools, production technologies, etc, co-evolve in a pattern of accelerating change.)

Randall Parker said at January 14, 2004 11:46 AM:

Fly, But have the wolves been getting smarter over the last 5 million years? I doubt it.

Also, today IQ is probably being selected against. Smarties have fewer kids than dummies.

Fly said at January 14, 2004 6:56 PM:

Randall, I’m guessing that the intelligence of many animals has been increasing slowly for millions of years. (Hmmm, what data might be available? Evidence for complex child rearing or hunting behavior in the early mammals?) I discussed wolves because they are social animals without hands or language but still pass on a learned culture. (A wolf reared in captivity and released into the wild doesn’t know how to survive or socialize in a pack.) My guess is that intelligence interacting with social culture results in a strong selection pressure for intelligence so wolf intelligence should increase faster than a non-social animal. Adding language and hands for tool use should greatly accelerate the process.

My post was prompted by the thinking of what factors would combine with intelligence to provide more selection pressure. Hence families of genes re-enforcing the selection advantage leading to a very fast increase in human intelligence. Admittedly this is after the fact reasoning. Humans are smartest so all the traits that characterize humans some how combined leading to our rapid increase in intelligence. Not very satisfactory. Presumably determining the mutation rate for the genes governing our distinguishing traits could test this idea.

Randall: “Also, today IQ is probably being selected against. Smarties have fewer kids than dummies.”

Based on my personal observation of friends and family, high IQ is not a successful breeding trait in the Western world. However the issue may be more complex. Very low intelligence also doesn’t contribute to successful breeding. Hard to know what’s really happening. Intelligent men may be fathering children on the wives of less intelligent men. I’ve also read that up to 20% of educated blacks in the US essentially have multiple wives. Combined with prison removing much of the breeding population who knows what is really happening? Who really knows what’s behind the Flynn effect.

Randall Parker said at January 14, 2004 7:25 PM:

Fly, I think the evidence on who is reproducing is pretty strong for the females at least. Read about the Australian Twin Registry study that showed less educated women have more kids.

Also, from the Imperial College London press release:

Part of the twin data analysis aimed to discover the effect that social, psychological and historical factors had on the number and timing of children born to the 2,710 pairs of twins studied.

The researchers found many of the variations in the threetraits were controlled by social factors such as religion and education (5). For example, Roman Catholic women had 20 per cent higher reproductive fitness than other religions. University educated women had 35 per cent lower fitness than those who left school as early as possible.

"I was staggered by the results we got," said Dr Owens. "When we decided to control for these factors, I wasn't expecting anything to come out of it. I thought, 'let's just run with the analysis'. But there was a massive difference in the number of children born to families with a religious affiliation. Many of the Catholic twins we studied had an average family of five children, where other families were having only one or two children.

"We also found that mothers with more education were typically having just one child at an older age. Their reproductive fitness was much lower than their peers who left school as early as possible. Again, and again, our analyses for these two factors came back with the same results."

The influence of religion and education in family size may seem an obvious finding - but what the scientists found really astonishing was that after controlling for these social factors, genetic changes were influencing the three life traits studied.

"Even after we controlled for these social factors, there was still lots of genetically heritable genetic variation in the three life history traits. This is a really unexpected finding."

However, he cautions against linking this work with the possibility of a eugenic programme for selective human breeding.

"Looking to the future, I would expect to pick up genetic changes within the ten generations (6) since industrialisation. However, what this work doesn't indicate or find, is a genetic marker for human reproduction - so you can't breed for early reproduction from our data. All the traits that we have examined are controlled by interactions between the environment and many genes."

The future work aims to understand more fully, the contribution psychological factors make, says Dr Owens. "We also want to repeat our experiments using twins databases elsewhere, to really put our results into a 'western world' context," he said.

Note that the politically correct thinking good Doctor Owen was staggered by his result, or at least he thought he ought to be. I have to laugh. Of course there is a strong correlation between intelligence and number of years of education. So unless smart men are knocking up dumb women (and I don't see anecdotal evidence for this) then we are in trouble.

Fly said at January 14, 2004 10:43 PM:

“Natural selection is still happening in humans right now. Unfortunately, as demonstrated by analysis of data from the Australian Twin Registry (ATR) published a couple of years ago in Evolution, the genetic variations for higher intelligence and delayed childbearing are being selected against in industrialized societies.”

If there are genes that influence mother instinct, they should be undergoing strong selection pressure now that most pregnancy is voluntary. Likely humans are also being selected to have more twins as such births are now less dangerous with modern nutrition and healthcare.

I’m not worried about breeding a world of "marching morons". I suspect that in the coming decades there will be biotech to enhance our minds. Likely we will also have brain computer implants to greatly augment brain function. Hence I’m not very concerned about mass immigration of uneducated Mexicans dragging the US down. In the future I don’t think our biological or cultural origins are going to matter all that much. Likewise I’m not worried about projections that Social Security or Medicare are going to bankrupt the country. Far greater changes are coming.

Randall Parker said at January 14, 2004 11:01 PM:

Fly, I don't share your complacency because things can go poorly in the short to medium term (heck, they are: look at California's high taxes and high state deficit for example) before technology saves us from the effects of current policy. Technology can not make us superbright now or 5 or 10 or 15 years from now. I want better quality of life for Americans this year. I want it next year. I want lower risk of crime and lower numbers of people on welfare and taxes that are as low as possible. Can't realize the best outcomes in the short and medium term with current immigration policy.

Brain computer implants: Still a very long way off. Heat dissipation is a huge problem. Look at how computers keep getting hotter. Of course, that heat dissipation also comes along with greater power needs in the first place. So where's the power going to come from?

Also, the first generations of brain computer implants are just going to be useful for accessing data. But once the data is presented the mind still has to make sense of it The biggest problem that holds back the less bright is they can't create complex models.

Selecting for twins: If there are any alleles that make twins more likely they will take many generations common enough to make a difference. But that is really orthogonal to the selection against IQ boosting alleles. Greater ability to have twins would either have no effect or will accelerate the rate at which IQ-boosting alleles are selected against.

Biological and cultural origins not mattering much: No, this is incorrect. Our beliefs that we have today and the instincts we have today will cause us to make decisions about the genetic programming for personality and conscience and behaviors related to ethics for future generations. Technology does not erase the effects of evolutionary history. Rather, our genes cause us to value different things and therefore it will cause us to value different alleles once we can choose alleles to give to offspring. There's no escape from our past.

Fly said at January 16, 2004 5:13 PM:

“Brain computer implants: Still a very long way off.”

Already exist for seizure control. Experimental treatment for deafness. Early, crude implants for retinal replacement. The future is now.

http://www.lorenbennett.org/nimplantseizure.htm

http://www.theage.com.au/articles/2004/01/08/1073437416730.html

http://www.optobionics.com/artificialretina.htm

Randall, I agree that a seamless interface from human to computer is a ways off. (Though I’m looking forward to my “memory” link to the world’s database so I can “remember” everything and my computational implant that performs all calculations and numerical simulations on the “fly”. Heehee.) In the near term I’m thinking more of direct electrical stimulation of brain regions to enhance learning, memory, concentration, etc. much as the vagus nerve stimulates the adrenal gland.

“Biological and cultural origins not mattering much: No, this is incorrect. Our beliefs that we have today and the instincts we have today will cause us to make decisions about the genetic programming for personality and conscience and behaviors related to ethics for future generations. Technology does not erase the effects of evolutionary history. Rather, our genes cause us to value different things and therefore it will cause us to value different alleles once we can choose alleles to give to offspring. There's no escape from our past.”

Randall, even today I feel more kinship with a medical researcher studying brain seizures in Mexico City than I do to my brother. Our worldviews and interests are similar even though our language, nations, and culture are quite different. With the changes I see coming in fifty years, I don’t think it’s going to matter all that much where a person was born.

At the same time I agree that we shouldn’t be complacent. We can’t just hope everything turns out all right. For me that means advocating policies that I believe will make the US a better country in the near and medium term. Partly that means awaking the public to the possibilities. Rather than fight to keep Medicaid expenses from growing I’d rather advocate more biotech research. Are you worried about the growing financial burden Alzheimer patients put on Medicaid then advocate significant increases for research in preventing and curing the disease. (I share your concerns regarding mass immigration and advocate similar policies. We differ more in the details than in the goal. Can’t get to next fifty years if US society doesn’t survive the next five, ten, and twenty years.)

Fly said at January 16, 2004 5:49 PM:

“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.”

Korean-American genius:
http://www.cnn.com/2003/EDUCATION/08/25/sprj.sch.wonder.kid.ap/

I’ve wondered how 1000 clones of this boy could change the world by accelerating research. (Or what a disaster if North Korea created a 1000 clones to help develop new weapons and strategies.)

Patrick said at January 17, 2004 11:28 PM:

Cloning a genius eh?

Einstein died too long ago, but Feinman was around well after cloning became a certainty. I wonder if anyone kept some tissue samples.

And would we get 100 physics geniuses? Or 2 physicists, 3 chemists, 2 great authors, a movie star, a rock legend, 5 billionaire business leaders, 2 drug cartel leaders, a dictator and a whole bunch of ordinary guys who just manage to have to high scores on the local video arcade games.

Fly said at January 18, 2004 12:25 PM:

Feynman would be good choice for cloning as he combined high IQ with creativity, fun and the ability to communicate. A Feynman clone might not be a great physicist or even exceptional in any field but he would have the potential for being great.

The Korean-American boy is fascinating because he is amazingly accomplished at such a young age. I doubt environment had much to do with his abilities. I give his mother credit for instilling social values that transform his native ability into real accomplishment.

The most brilliant person I’ve known only graduated from college because his math professors waived degree requirements. Decades later I heard he never completed his PhD in mathematics. He either couldn’t or wouldn’t write down his discoveries in a form acceptable for a doctoral thesis. I doubt he’s made any significant contribution to society. Another genius dropped out of school to work in his brother’s Go-Cart track. So yeah, I agree that a high IQ doesn’t guarantee a person will make valuable contributions to society.

Iourii Gribov said at January 19, 2004 6:15 AM:

We are made by our genes, but our genes evolution reflects long evoution of our compicated adaptation .
My research field is psychology of creativity (the neuropsyclogcal nature of creative abities)

I studied 3 years (before Moscow University - physical faculty) in the Univ. school for gifted school pupiles.
There were few relatively very young boys with phantastic IQ and memory. Later I was in friendship with one of them.I
was surprised, that he (and some other similar students ater graduating Univ.) could not reach something exeptional, as I could wait. His majour problem was - he was not enough creative and simply did not now how to use his huge intellect.
I think that in the intellect/genes studies scientiests must also account (as very important) creative potential. This potentil also must have genetic roots and I wlii be glad to hear about this subject and possibly participate in the such inestigations. Now I am looking for a e.g. postdoc position, but ny way wil be interesten some relevant information.

Sincerely, Iourii Gribov T/F 0049 30 21767010

Iourii Gribov said at January 19, 2004 6:19 AM:

I forgot to add my email: IGribov@aol.com

Marc van der Erve said at April 6, 2004 5:24 AM:

Creativity, not IQ, is the functionally significant trait that distinguishes the surviving human species. It is the drive (maybe more than the ability) to venture into new environments (and survive).

Creativity is a chicken-and-egg kind of matter.

Did creativity make the human species a migrating phenomenon (unlike birds often not returning from where they came) or did a physical or environmental situation create the "need" that "favored" those of the human species that had the urge to move about?

Following the same line of thinking: "Religions may produce the opposite of what they claim." Certain, if not most of current-day religions lock up the human species with a strictly-defined social environment. As such, they go against the human nature to migrate to other, unknown (social) environments that unlock and/or stimulate the emergence of other traits.

fincher said at December 30, 2004 9:35 AM:

hi guys,
ok, it is definitely possible that aliens improved the species--within limits--
it is also possible that aliens ruined the species--
within limits--
now, there has to be a study done with volunteers, who can absolutely be selected based on not having the Abnormal Spindle-Like Microcephaly Associated (ASPM) gene--or, more simply put--on fly's and the other guys heads--
the X factor gene improvement is baloney--it is more likely that some combination allows two genes to combine and that a "large" percentage of the population gains the "new, improved, dominant" gene version simultaneously--an invading army for example impregnates a different group of women--presto--smart people get born in one generation--
this one by one expansion over millions of years and selection of one smart person who has 10 kids who become smart and then they have 10 kids who become smart who then have 10 kids who become smart--etc. etc etc--nonsense--
aliens definitely improved chimps and are due to arrive according to superresearcherfincher's calculations--next year--

Kyle Janison said at February 13, 2005 5:08 PM:

There's a great new astrobiology blog, run by newspaper editor Rob Bignell, at http://alienlifeblog.blogspot.com/. It includes roundups of the latest news from the various scientific fields that form astrobiology and information about the evolution of human intelligence.

Kyle P said at September 25, 2008 11:38 PM:

I would like to return to the original topic (although alien conspiracy's may be fun and intriguing). As there is still a great deal of speculation over the nature vs nurture argument, (studies with twins can sometimes show stark similarities which are statistically improbable. But also environment has been shown to influence peoples choices and developmental psychology. e.g. many serial killers and mentally disturbed people had rough or in some cases horrid lifestyles). And as of today many scientists (including myself) have a general consensus over nature/nurture both having effects on development.

Of course this might be stating the obvious, but ultimately it seems that only cases such as that with "proteges" or "gifted" children excite reference to superior genes. But this notion seems to undermine the effects that a healthy and prominent developmental scheme can have on a supposedly "normal" mind. Another factor that people tend to not notice is that many of these "proteges" are debuted when they are discovered, but few of them are remembered throughout history, (and some of the more recent "gifted" students are barely maintened beyond that point).

On the other hand some of our most revered scientists and entrepreneurs were in fact not perfect and some (including Einstein himself) were actually diagnosed by "the powers that be" as mentally disabled, due to their lack of communication skills. Using Einstein as a prime example, he had a lot of difficulty learning throughout elementary school and was in some ways held back, until he met a friend who showed Einstein an alternative method of memorization. Soon after he was rising to the top of his classes and planting the seeds of general relativity and theoretical physics. So ultimately when it comes to viewing intelligence it can never be taken at face value due to the immense behavioral and cognitive characteristics which each individual (even twins) has uniquely to themselves.

Anonymous said at May 7, 2011 4:26 PM:

If you want to read a good article about Human intelligence follow this link http://www.progressivehumanism.com/progressive-humanism/on-human-intelligence/

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