Friday, 3 April 2015

How Europeans Evolved

Archetypal European hunter-gatherer
How Europeans evolved white skin | Science/AAAS | News

A new study has provided more detail on the discovery reported a year ago that Europeans evolved white skin fairly rapidly about 8000 years ago but not, as one might assume, in Europe itself but rather in three different distinct populations of hunter-gatherers and farmers who moved into Europe, each contributing genes to the 'European' genome.

A paper published in February this year showed that the origin of the Indo-European languages was probably a population of nomadic herders from the Russian steppe north of the Black Sea who appear to have migrated massively into Europe about 4500 years ago. These people are known as the Yamna Culture. Indo-European languages exist now in about 400 different languages and dialects from Irish in the west to Hindi and Urdu in the east.

This migration has now been confirmed by genetic studies on 83 ancient remains from archaeological sites across Europe. However, this study has also shown that these hunter-gatherers were lactose intolerant as they didn't have the version of the LCT gene which allows the digestive enzyme lactase, which digests the lactose in milk, to persist into adulthood. Nor could they digest milk itself.

The same goes for the first farmers who came into Europe from the Near East about 7800 years ago.

The new data also shows that the third group, the people who had probably been in Europe for about 40,000 years, were dark skinned like their African ancestors because they lacked the SLC24A5 and SLC45A2 genes which lead to de-pigmentation in Europeans, but further north these people were light skinned, having the light-skin versions of the SLC24A5 and SLC45A2 genes and also a third gene, HERC2/OCA2 associated with blond hair and blue eyes.

As the farmers from the Near East moved into Europe they interbred with the 'indigenous' people and the SLC45A2 gene spread rapidly through the population, followed more slowly by the SLC24A5 gene after about 5800 years ago.

The rapid spread of the genes for pale skin suggests strong selection pressure favouring them and there are two likely candidates, although the team who did this study don't speculate:
  1. Dark skin in tropical latitudes protects against skin cancers by filtering out harmful UV light while letting enough through for the skin to manufacture enough vitamin D to supplement any dietary deficiency. In northern latitudes as the sun weakens and the skies become cloudier, the balance shifts towards paler skin to allow enough vitamin D production at the expense of increased skin cancers.
  2. Sex selection.

As the diet changed with the spread of agriculture and increased dependence on cereals, loss of dietary vitamin D might have been a major factor in this shift of this balance in favour of paler skin in northern climates.

However, another mutation to give lactase persistence and the ability to digest lactose and milk, which is believed to have arisen and spread rapidly in Europe about 4300 years ago, probably swung the balance back a little especially further south because milk is a source of dietary vitamin D in children. There are also other probable factors in this rapid spread in a population with access to cattle milk because it enables a mother to wean a baby onto cattle milk, so removing the natural contraception which comes from breast feeding, enabling her to produce more offspring.

Meanwhile, the Yamnaya people from the Russian steppe had greater genetic potential for providing genes for height, which is a complex trait and appears to have also spread rapidly in central and northern Europe but, for some reason, less so on Italy and Spain.

So we have genetic evidence of three different people, both genetically and culturally, each contributing to the range of people we now think of as Europeans and all this happening in that last 8000 years.

The bad news for creationists, and especially the extreme right-wing white supremacist Christians, who like to assume white Europeans are somehow racially pure and were specially favoured by their creator god, is that this shows how Europeans are nothing of the sort. They are a fairly recent hybrid between several locally-evolved variants, each of whom contributed genes which gave an advantage in the particular European conditions, showing how mixing, not isolation, produces a better long-term outcome through evolution by natural selection and so better adaptation to local conditions. No one population, skin colour or physical type is superior to any other; each is equally well evolved to suit the local conditions in which they evolved.

Even those creationists who haven't been fooled by the racists amongst their leadership will find it difficult to explain how all this diversity arose in the last 6000 years from a very small founder population of a man, his sons and their wives, not only in Europe, but in the rest of the world where these sorts of evolutionary processes will have produce the present-day people, and to account for this genetic evidence of dynamic evolution by natural selection, in a people their creation myth tells them was created, perfectly made, as it is today.

Any takers?

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