Thursday, 11 June 2015

Mutant Europeans

Yamnaya skull from the Samara region colored with red ochre.
Photo Credit: Natalia Shishlina
Nomadic herders left a strong genetic mark on Europeans and Asians | Science/AAAS | News

More news yesterday on the subject of the origins of Euro-Asian people and in particular, lactase persistence in Europeans, which should, if they understood it, be causing creationists to rethink their superstitions.

So, if you've fallen for the 'Intelligent Design' hoax and want to stay duped, or if you need to believe you have a close personal relationship with the creator of the Universe so you feel important enough, stop reading now because there will be some hard questions at the end designed to make you think.

The news comes from two rival teams of geneticists who analysed the DNA from a total of 170 individuals from archaeological sites in Europe and Asia. These people lived between 3000 and 5000 years ago so covering the period when the Bronze Age spread from the Middle East out into Europe and Asia. The debate has always been about whether this was a spread of ideas as neighbours learned the new technology, or whether it was spread by people who brought the new technology with them as they migrated across the continent.

The genetic evidence now shows that it was almost certainly the latter and the people we have to thank for it were a group of nomadic people from what is now the steppes of Ukraine and Russia known to anthropologists as the Yamnaya. Their original homeland was the vast area north of the Black Sea and stretching east to the Caspian.

The Bronze Age of Eurasia (around 3000–1000 BC) was a period of major cultural changes. However, there is debate about whether these changes resulted from the circulation of ideas or from human migrations, potentially also facilitating the spread of languages and certain phenotypic traits. We investigated this by using new, improved methods to sequence low-coverage genomes from 101 ancient humans from across Eurasia. We show that the Bronze Age was a highly dynamic period involving large-scale population migrations and replacements, responsible for shaping major parts of present-day demographic structure in both Europe and Asia. Our findings are consistent with the hypothesized spread of Indo-European languages during the Early Bronze Age. We also demonstrate that light skin pigmentation in Europeans was already present at high frequency in the Bronze Age, but not lactose tolerance, indicating a more recent onset of positive selection on lactose tolerance than previously thought.

They also brought their language with them. This is now believed to have been the original Proto-Indo-European language, the ancestor of some 400 languages spoken across Europe and much of Asia and the Indian sub-continent. Quite where this language group had its origins has long been a matter for debate amongst linguists so what we are seeing here is another of those examples of different strands of science homing in on the same answer.

This neatly illustrates something that creationists seem to find hard to understand - evidence-based science will always home in on a single truth because, for example, people migrating take both their language and their DNA with them, so since both modern DNA and modern languages have evolved from these same ancestral groups, convergence on the question of origins is exactly what we would expect.

We generated genome-wide data from 69 Europeans who lived between 8,000–3,000 years ago by enriching ancient DNA libraries for a target set of almost 400,000 polymorphisms. Enrichment of these positions decreases the sequencing required for genome-wide ancient DNA analysis by a median of around 250-fold, allowing us to study an order of magnitude more individuals than previous studies and to obtain new insights about the past. We show that the populations of Western and Far Eastern Europe followed opposite trajectories between 8,000–5,000 years ago. At the beginning of the Neolithic period in Europe, ~8,000–7,000 years ago, closely related groups of early farmers appeared in Germany, Hungary and Spain, different from indigenous hunter-gatherers, whereas Russia was inhabited by a distinctive population of hunter-gatherers with high affinity to a ~24,000-year-old Siberian. By ~6,000–5,000 years ago, farmers throughout much of Europe had more hunter-gatherer ancestry than their predecessors, but in Russia, the Yamnaya steppe herders of this time were descended not only from the preceding eastern European hunter-gatherers, but also from a population of Near Eastern ancestry. Western and Eastern Europe came into contact ~4,500 years ago, as the Late Neolithic Corded Ware people from Germany traced ~75% of their ancestry to the Yamnaya, documenting a massive migration into the heartland of Europe from its eastern periphery. This steppe ancestry persisted in all sampled central Europeans until at least ~3,000 years ago, and is ubiquitous in present-day Europeans. These results provide support for a steppe origin of at least some of the Indo-European languages of Europe.

Massive migration from the steppe was a source for Indo-European languages in Europe
Wolfgang Haak, et. al.
Nature 522, 207–211 (11 June 2015) doi:10.1038/nature14317

Both archaeologists and linguists have had theories about how cultures and languages have spread in our part of the world. We geneticists have now collaborated with them to publish an explanation based on a record amount of DNA-analyses of skeletons from the Bronze Age.

Assistant Professor Morten Allentoft
Centre for GeoGenetics,
Natural History Museum of Denmark,
University of Copenhagen
Contrast this with religion where different religions looking at the same topic will rarely agree and will more likely diverge, and where even a single religion can easily split into rival sects over the same issue. This is because there is no neutral evidence to 'referee' in the debate, and even if there were, it would simply be dismissed as 'wrong' by one or both rival camps. In science, the conclusion is open and the facts are neutral; in religion, the conclusion is sacred so facts are irelevent.

Anyway, back to our migrating nomads.

What these people didn't take with them was pale skin or the ability to digest milk into adulthood. Pale skin was already present in some northern populations, which means they were probably experiencing evolutionary pressures due to a change in the balance between the need to manufacture vitamin D in their skin and the need to filter out UV sunlight to avoid skin cancers.

The variant of the LCT gene which produces lactase in adults and so enables the carriers to digest the lactose found in milk, was scarce in both the indigenous Europeans and the migrants. The conclusion then is that this mutation has arisen and spread through most of Europe in the last 2000 years, and this is significant from an evolutionary point of view as well as for dupes of the Intelligent Design hoax.

For a longer discussion of lactase persistence, see my blog Lactose Tolerance And Creation 'Science'. Briefly, lactose intolerance, which is the inability to digest the sugar lactose found in milk. This condition is rare in Europeans but is common in most of the rest of the world. In fact, lactose tolerance is actually the mutant 'abnormal' condition.

The reason humans, like many other mammals, stop digesting milk in early childhood is because breast-feeding is a natural contraceptive - suckling induces the production of a hormone which inhibits ovulation. This ensures that a new baby has a monopoly of the mother for the first year or so. But, to balance that, the baby eventually weans and allows the mother to ovulate again, so producing more children. There is an evolutionary balance between the baby monopolising the mother and so improving its chance of surviving, and the mother producing more babies. Suckling too long and the number of babies being born falls; weaning too soon, or failing to inhibit ovulation, and the number of surviving babies falls.

Now, change a couple of things in the environment.

Previously the common belief was that lactose tolerance developed in the Balkans or in the Middle East in connection with the introduction of farming during the Stone Age. But now we can see that even late in the Bronze Age the mutation that gives rise to the tolerance is rare in Europe. We think that it may have been introduced into Europe with the Yamnaya herders from Caukasus but that the selection that has made most Europeans lactose tolerant has happened at a much later time.

Associate Professor Martin Sikora,
Centre for GeoGenetics
The availability of other sources of milk (cattle, sheep goats) - and humans can replace mother's milk with an alternative. This means that grandparents, aunts, uncles, older siblings, etc can now feed baby and the mother can produce more babies. Babies get the benefit of prolonged milk feeding and mothers get the benefit of losing natural contraception (or rather her genes get a benefit from it).

Pale skin (indicating a vitamin D deficient diet). As this study also showed, pale skin was also developing in northern parts of Euro-Asia, almost certainly because of another evolutionary trade-off. Human skin probably became pigmented as we lost body hair to filter out harmful UV sunlight which cause skin cancer. However, humans also manufacture the essential vitamin, vitamin D, in their skins to supplement a diet normally deficient in it.

It seems like the Bronze Age is the period where the genetic diversity and distribution that we know today is basically formed...

The ability to drink milk is a very unique European feature - you also find it in a few African groups, but there it is due to different mutations.

Professor Eske Willerslev, University of Copenhagen, Denmark.
(Interview with BBC News.)
So, in Northern Europe, humans almost certainly got a double benefit from carrying the LCT mutant which enabled them to digest milk into adult hood. They already had domestic animals which provided it and so had probably been giving it to their children. The children carrying the mutant gene could now carry on drinking milk, so getting a vitamin D supplement as well as the additional calories from a food source which came in to be milked.

This win-win situation which produced more, more healthy children and used a food source derived ultimately from inedible (to humans) grass and scrub, was very probably the reason that lactase persistence spread rapidly through out the European population in as little as 2000 years.

So now to the questions for creationists, especially those who have fallen for the Intelligent Design hoax:

Why would an intelligent designer create humans with both skin and a digestive system suited to living in Africa without domestic cattle, and then have to change them to make them suitable to live in Europe, and why did it wait until 2000 - 3000 years ago before designing them to use the surplus of milk their domestic animals had been producing for so long, then restrict this to just a few populations?

How does this genetic and linguistic evidence of the migration into Europe and Asia from a centre in what is now modern Ukraine and Russia some 3000 - 5000 years ago tie in with a story of all humans being descended from a single ancestral family who survived a flood some 4000 years ago?

Please try to avoid abuse and Bible quotes in your answers because they're just unnecessarily wordy way of telling people you don't know and you're not prepared to think about it.

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