2012 September 02 Sunday
Denisovan Girl Died 80,000 Years Ago

Neandertals aren't the only hominin line that branched off from humans a long time ago and later bred with humans. Ancient hominins named Denisovans (after a Siberian cave where their remains were found) bred with humans as shown by DNA sequence comparison. Recently scientists in Svante Pääbo's lab did a full DNA sequence of a Denisovan girl who died tens of thousands of years ago in Siberia.

In a stunning technical feat, an international team of scientists has sequenced the genome of an archaic Siberian girl 31 times over, using a new method that amplifies single strands of DNA. The sequencing is so complete that researchers have as sharp a picture of this ancient genome as they would of a living person’s, revealing, for example that the girl had brown eyes, hair, and skin. “No one thought we would have an archaic human genome of such quality,” says Matthias Meyer, a postdoc at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany. “Everyone was shocked by the counts. That includes me.”

The Denisovan girl might have died 80,000 years ago. See the Scientific American coverage by Katherine Harmon for implications this discovery has for migrations of early humans.

Modern humans come from a branch that split off from Denisovans a few hundred thousand years ago.

The analysis suggests that the modern human line diverged from what would become the Denisovan line as long as 700,000 years ago—but possibly as recently as 170,000 years ago.

Bringing Denisovans back to life would let us better study the effects of their genetic variants. Suppose it is found that the Denisovans have some genetic variants that would be useful in humans. Should it be legal to add these genetic variants into human offspring?

I expect scientists who work with cell cultures will do something less radical first: integrate sections of Denisovan DNA into human cells in culture. Then watch how their genes get expressed in different conditions in cell culture. If scientists integrate some of that DNA into lab mice then Denisovan DNA expression could be studied even more realistically.

By Randall Parker    2012 September 02 02:23 PM   Entry Permalink | Comments (0)
2008 December 31 Wednesday
Neanderthals Lost Out From Competition Not Climate Change

The Neanderthals were out-classed by the upstarts and just couldn't compete.

In a recently conducted study, a multidisciplinary French-American research team with expertise in archaeology, past climates, and ecology reported that Neanderthal extinction was principally a result of competition with Cro-Magnon populations, rather than the consequences of climate change.

The study, reported in the online, open-access journal PLoS ONE on December 24, figures in the ongoing debate on the reasons behind the eventual disappearance of Neanderthal populations, which occupied Europe prior to the arrival of human populations like us around 40,000 years ago. Led by Dr William E. Banks, the authors, who belong to the French Centre National de la Recherche Scientifique, l'Ecole Pratique d'Hautes Etudes, and the University of Kansas, reached their conclusion by reconstructing climatic conditions during this period and analyzing the distribution of archaeological sites associated with the last Neanderthals and the first modern human populations with an approach typically used to study the impact of climate change on biodiversity.

This method uses geographic locations of archaeological sites dated by radiocarbon, in conjunction with high-resolution simulations of past climates for specific periods, and employs an algorithm to analyze relationships between the two datasets to reconstruct potential areas occupied by each human population and to determine if and how climatic conditions played a role in shaping these areas. In other words, by integrating archaeological and paleoenvironmental datasets, this predictive method can reconstruct the regions that a past population could potentially have occupied. By repeating the modeling process hundreds of times and evaluating where the errors occur, this machine-learning algorithm is able to provide robust predictions of regions that could have been occupied by specific human cultures.

In a few weeks I'm going to review an exciting new book that, among other claims, argues humans benefited from an introgression (in flow) of Neanderthal genes that helped humans evolve more rapidly. So not only did our ancestors wipe out Neanderthals but humanity even gained genetically from the interaction.

Why didn't Neanderthals instead take some of our genes and out-compete early modern humans? Not sure. I can think of some possibilities. Even if the hybrids possessed some advantages they existed in small numbers. The beneficial genetic alleles humans gained from Neanderthal genes might not have become widespread until well after Neanderthal numbers had greatly dwindled. Humans might have had such large competitive advantages that Neanderthals couldn't absorb beneficial human genes fast enough to be able to compete. Also, maybe the hybrids were more often born in human communities than in Neanderthal communities. Or maybe humans were more accepting of raising hybrids.

Anyone have a clue on this?

By Randall Parker    2008 December 31 03:40 PM   Entry Permalink | Comments (9)
2008 October 21 Tuesday
Sexual Bonobos Kill Other Primates

The 1960s dream of "make love, not war" does not work for Bonobos. Even though bonobo societies are characterized by promiscuity and a lack of male dominance the males still hunt and kill other primate species.

Unlike the male-dominated societies of their chimpanzee relatives, bonobo society—in which females enjoy a higher social status than males—has a "make-love-not-war" kind of image. While chimpanzee males frequently band together to hunt and kill monkeys, the more peaceful bonobos were believed to restrict what meat they do eat to forest antelopes, squirrels, and rodents.

Not so, according to a study, reported in the October 14th issue of Current Biology, a Cell Press publication, that offers the first direct evidence of wild bonobos hunting and eating the young of other primate species.

Competition among primates is unavoidable since resources are limited. Short of genetic engineering I doubt that will change. Even without male dominance in bonobo societies they still go killing other primates.

"These findings are particularly relevant for the discussion about male dominance and bonding, aggression and hunting—a domain that was thought to separate chimpanzees and bonobos," said Gottfried Hohmann of the Max-Planck-Institute for Evolutionary Anthropology. "In chimpanzees, male-dominance is associated with physical violence, hunting, and meat consumption. By inference, the lack of male dominance and physical violence is often used to explain the relative absence of hunting and meat eating in bonobos. Our observations suggest that, in contrast to previous assumptions, these behaviors may persist in societies with different social relations."

Bonobos live only in the lowland forest south of the river Congo, and, along with chimpanzees, they are humans' closest relatives. Bonobos are perhaps best known for their promiscuity: sexual acts both within and between the sexes are a common means of greeting, resolving conflicts, or reconciling after conflicts.

The researchers made the discovery that these free-loving primates also hunt and kill other primates while they were studying a bonobo population living in LuiKotale, Salonga National Park, in the Democratic Republic of Congo. They had been observing the bonobos there for the last five years, which is what made the new observations possible.

By Randall Parker    2008 October 21 08:54 PM   Entry Permalink | Comments (6)
2008 August 09 Saturday
Neanderthal Mitochondrial DNA Fully Sequenced

Our cells contain organelles called mitochondria which break down sugar to provide energy. Those organelles have their own small genome separate from the very large genome found in almost every cell nucleus (excepting red blood cells). A scientific team in Germany has now successfully sequenced the mitochondrial DNA of Neanderthals. Using that information these scientists have calculated that Neandertals and humans went their separate ways about 660,000 years ago.

A study reported in the August 8th issue of the journal Cell, a Cell Press publication, reveals the complete mitochondrial genome of a 38,000-year-old Neandertal. The findings open a window into the Neandertals' past and helps answer lingering questions about our relationship to them.

" For the first time, we've built a sequence from ancient DNA that is essentially without error," said Richard Green of Max-Planck Institute for Evolutionary Anthropology in Germany.

The mitochondrial DNA is only about 15,000 letters (a little less). So by itself it doesn't tell us much about the vast bulk of ways that humans and Neandertals differ. But that amount of information is enough to estimate how far the two species formed separate from each other.

Analysis of the new sequence confirms that the mitochondria of Neandertal's falls outside the variation found in humans today, offering no evidence of admixture between the two lineages although it remains a possibility. It also shows that the last common ancestor of Neandertals and humans lived about 660,000 years ago, give or take 140,000 years.

Here's the really interesting part: We might some day have a complete Neanderthal genome sequence.

Scientists eventually hope to sequence a full Neanderthal genome.

That information would open up the possibility of eventually bringing Neanderthals back to life. What do you think of doing this?

Suppose some billionaire bankrolled the cloning of a Neanderthal. On what basis should we decide whether to grant it human rights? Suppose it has an IQ in the lower range for humans (say 80). But suppose it was totally hostile to us and dangerous. Should it be granted full rights? Or a subset of rights?

The ability to create creatures that are closer to humans than existing primates will force us to come up with far more precise criteria for what should be granted rights. We already grant subsets of rights to children and even to some adults. People imprisoned or committed to mental hospitals do not have all rights. But a Neanderthal or perhaps a dog or pig or lion genetically engineered to have low human IQs would pose much more complicated questions about why we grant rights. Imagine a 100 IQ creature who we could know will try to kill us. Imagine a 90 IQ creature that will not try to kill us or try to rob or otherwise harm us. Do we grant full rights to the latter while keeping the smarter but more dangerous creature in a sort of zoo?

By Randall Parker    2008 August 09 01:04 PM   Entry Permalink | Comments (10)
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