The people who built Stonehenge 5000 years ago probably had the same pallid complexion of many modern inhabitants of the UK. Now it seems that the humans occupying Britain and mainland Europe only lost the darker skins of their African ancestors perhaps just 6000 years earlier, long after Neanderthals had died out. The finding confirms that modern Europeans didn’t gain their pale skin from Neanderthals – adding to evidence suggesting that European Homo sapiens and Neanderthals generally kept their relationships strictly platonic.
There is a clear correlation between latitude and skin pigmentation: peoples that have spent an extended period of time at higher latitudes have adapted to those conditions by losing the skin pigmentation that is common at lower latitudes, says Sandra Beleza at the University of Porto in Portugal. Lighter skin can generate more vitamin D from sunlight than darker skin, making the adaptation an important one for humans who wandered away from equatorial regions.
Those wanderings took modern humans into Europe around 45,000 years ago – but exactly when the European skin adapted to local conditions had been unclear.
Three genes
Beleza and her colleagues studied three genes associated with lighter skin pigmentation. Although the genes are found in all human populations, they are far more common in Europe than in Africa, and explain a significant portion of the skin-colour differences between European and west African populations.
By analysing the genomes of 50 people with European ancestry and 70 people with sub-Saharan African ancestry, Beleza’s team could estimate when the three genes – and pale skin – first became widespread in European populations. The result suggested that the three genes associated with paler skin swept through the European population only 11,000 to 19,000 years ago.
“The selective sweeps for favoured European [versions of the three genes] started well after the first migrations of modern humans into Europe,” says Beleza.
The finding agrees with earlier studies suggesting that modern humans did not lose their dark skins immediately on reaching Europe, says Katerina Harvati at the University of Tübingen in Germany. “[The new study] is interesting because it suggests a very late differentiation of skin pigmentation among modern humans,” she says.
An earlier analysis of ancient DNA in 40,000 and 50,000-year-old Neanderthal bones, respectively from Spain and Italy, suggested that our extinct cousins had light-coloured skin and reddish hair in their European heartland. But the Neanderthals went extinct around 28,000 years ago – long before modern humans in Europe gained a pale skin. Evidently Neanderthals did not pass these useful local adaptations on to modern humans, despite genetic evidence that the two species interbred.
Middle Eastern contact
That might seem unusual given that the two species lived cheek-by-jowl in Europe for several thousand years. But it makes sense if the interbreeding evident in the genes occurred in the Middle East, where modern humans and Neanderthals first met, says Chris Stringer at the Natural History Museum, London.
In that region, Neanderthals may have had darker skins, explaining why our species did not gain a pale skin after interbreeding with them. Indeed, a study earlier this year of ancient DNA suggested that Neanderthals living in what is now Croatia had dark skin and brown hair.
“Neanderthal skin colour was probably variable, as might be expected for a large population spread out over a large territorial expanse,” says Harvati.
Journal reference: Molecular Biology and Evolution, doi.org/h9h
Source: http://www.newscientist.com
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