The Legacy Of Sex With Neanderthals

Neanderthal-human sex bred light skins and infertility - life - 29 January 2014 - New Scientist

Modern techniques of DNA recovery, sequencing and analysis are quickly adding enormously to our understanding of the human evolutionary story, at a rate which must be terrifying to the professional liars at the Discovery Institute and the Institute for Creation Research whose job it is to either rubbish the science or distort it to make it look like creationists have a rational scientific point of view.

Take for example the three new studies published recently which shed more light on how Euro-Asian humans interacted with Neanderthals. Neanderthals (Homo neanderthalensis) are believed to have evolved from the close ancestors of 'modern' humans (H. sapiens), possibly H. heidelbergensis or H. erectus which migrated out of Africa and dispersed into Europe and Asia some 200,000 years ago, leaving those behind in Africa to evolve into H. sapiens, who followed them out in a second exodus, some 65,000 years ago and where they then co-existed as separate human species for some 35,000 years. It could be that we owe much of our success to our sister species who went before us.

It was once believed that there was no interbreeding between H. sapiens and H. neanderthalensis until the Neanderthal genome was successfully isolated and sequenced. It was then found that non-African H. sapiens have between 1% and 3% Neanderthal DNA showing beyond doubt that interbreeding had taken place.

Now detailed analysis of the genomes of 1004 people by Sriram Sankararaman, David Reich and colleagues of Harvard Medical School has revealed that Neanderthal DNA tends to be concentrated in regions of the genome with greatest variability, making these genes more susceptible to natural selection and so contributing more to our evolution. So, although forming a relatively small proportion of the genome, Neanderthal genes could have contributed disproportionately to our evolution, especially into a northern, temperate climate.

Meanwhile, a second study by Joshua Akey and Ben Vernot of the University of Washington in Seattle has shown that Neanderthal genes tend to be clustered around those associated with keratin production. Keratin is the structural fibrous protein found in skin, nails and hair. This finding was also supported by the Harvard study.

One of the genes involved was that producing pale skin, which is an advantage in cloudy northern climates where skin cancer is less of a problem and where Vitamin D, which is produced in the skin under the influence of sunlight and which is essential for normal bone development in children, can be deficient, especially if the sunlight is filtered out by pigmentation. So we have the possibility that Neanderthal genes provided us with paler skin.

However, this may be contradicted by a third study published in Nature by Iñigo Olalde, Morten E. Allentoft and colleagues of the genome of a single Stone Age European who lived about 7000 years ago near León, Spain had dark skin. Of course we can't project this finding onto all Europeans from 7000 years ago but it shows that pale skin was not then a universal European trait. This was some 40,000 after interbreeding between H. sapiens and Neanderthals could have taken place, so it they contributed to European pale skin, it was slow to spread throughout the European H. sapiens gene pool.

The question then is did Neanderthal keratin genes give us straighter hair than our African ancestors?

This underlines that modern humans and Neanderthals are indeed different species.

Fred Spoor, The Max Planck Institute for Evolutionary Anthropology, Leipzig, Germany

Other findings by the Harvard study show that not all Neanderthal genes were beneficial. Some seem to have made us more susceptible to autoimmune diseases such as type II diabetes, lupus and Crohn's Disease. It has previously been suggested that they could have made us more susceptible to arthritis in later life. They also found an almost complete absence of any Neanderthal genes on the sex-determinant X chromosome, suggesting that, when these were passed on they may have caused infertility and so would have been quickly eliminated. This is a common problem when related but distinct species interbreed, reinforcing the idea that Neanderthals had evolved into a distinct species, not a subspecies or merely a local variant, as had earlier been thought.

Because Neanderthal DNA is clustered in the H. sapiens genome rather than being more evenly admixed within it, this suggests that inter-breeding was a rare event. Sriram Sankararaman goes so far as to estimate that it may have happened only four times.

If this is so, it may well be that it was always H. sapiens male mating with H. neanderthalensis females since Neanderthal Y chromosomes, which are always inherited only from the father, have never been recovered from modern humans. Of course, this could also be because they are so rare that we just haven't found one yet - which doesn't square with Neanderthal DNA being found in all non-African humans. It could also indicate that a Neanderthal father and an H. sapiens mother always produced offspring with reduced fertility, or even sterile offspring.

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