F Rosa Rubicondior: Getting To Know Your Inner Neanderthal

Friday 6 October 2017

Getting To Know Your Inner Neanderthal

The Contribution of Neanderthals to Phenotypic Variation in Modern Humans: The American Journal of Human Genetics.

We've know for some years now that modern non-African humans have some Neanderthal DNA. This must have been acquired by interbreeding during the comparatively brief period between the migration of anatomically modern humans (AMHs) out of Africa about 50-60,000 years ago and 40,000 years ago when Neanderthals went extinct.

We also know that this interbreeding was not entirely successful and probably didn't always produce viable offspring. For example, there are no known examples of either Neanderthal Y chromosomes in modern humans, nor are there examples of Neanderthal mitochondrial DNA (mtDNA). This suggests that male Neanderthal - female AMH mating did not produce viable male offspring. It also suggests that either female Neanderthal - male AMH did not produce viable females or that females remained 'Neanderthal' and became extinct with them or did not contribute further to the AMH gene-pool carrying their mtDNA with them.

We also know that many of the Neanderthal genes proved to be deleterious and were quickly eliminated because the Neanderthal DNA we now have is heavily clustered and absent from many of our chromosomes altogether. Clustering tends to be around those chromosomes and those genes associated with our immune system, and skin and hair colour and type. In other words, we kept the genes that helped us adapt to a northern climate and possible new pathogens and got rid of a lot that may have been harmful - although not all of them since our 'improved' immunity might have been at the expense of inheriting a disposition to auto-immune diseases.

But one of the problems in identifying exactly what DNA we have retained as a population and particularly how this affects our genome has been the relatively small cohort of AMH DNA available for analysis and how representative this is of the population as a whole. A previous study of the DNA from 28,000 people in the eMERGE Network appeared to show an association between obesity and Neanderthal DNA which was not found in this study. The authors suggest that this could be due to the fact that the eMERGE DNA was from people already undergoing medical treatment.

This new study used a cohort of 112,338 individuals from the UK Biobank database.

After humans and Neandertals met many thousands of years ago, the two species began interbreeding. Although Neandertals aren't around anymore, about two percent of the DNA in non-African people living today comes from them. Recent studies have shown that some of those Neandertal genes have contributed to human immunity and modern diseases. Now researchers reporting in the American Journal of Human Genetics on October 5th have found that our Neandertal inheritance has contributed to other characteristics, too, including skin tone, hair color, sleep patterns, mood, and even a person's smoking status.

The researchers found that Neanderthal alleles were associated with both lighter and darker skin tones as well as the ability to tan in sunlight. This suggests that Neanderthals too varied in their skin tone and ability to tan just like non-African AMHs. We appear to have got this ability to adapt to variable amounts of sunlight from Neanderthals that might have taken 200,000 years to evolve it. Contrary to popular myth however, the team found no evidence of the genes for red hair in the Neanderthal genes.

Neanderthal alleles were also associated with mood changes, circadian rhythms. Change in skin tone, mood changes, circadian rhythms and sleep patterns are all linked to sunlight exposure so it seem probable that these genes were acquired from Neanderthals and have been retained by non-African AMHs because they conveyed and adaptive advantage in a northern climate.

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