"Ten Thousand Years of Natural Selection in Europe"

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Wednesday, March 08, 2017 4:00pm - 5:00pm
Watson CIT - SWIG Boardroom (CIT241)

Dr. Iain Mathieson
Postdoctoral Research, Reich Lab - Harvard Medical School

"Ten Thousand Years of Natural Selection in Europe"

The development of agriculture beginning around twelve thousand years ago signaled the start of one of the most dramatic lifestyle changes in human history: from small groups of hunter-gatherers to large, settled, complex agricultural societies. In Europe, pre-existing hunter-gatherer groups disappeared between about 6,400 and 3,000BCE, to be replaced with much denser agricultural populations. Ancient DNA from individuals who were part of these groups has, in the past few years, shown conclusively that this change in lifestyle was accompanied by a massive migration of people into Europe from Anatolia, ultimately derived from the first farmers of the Levant. 

As these Early Farmers move into Europe and mixed with existing populations, they experienced dramatic changes in diet, environment and social organization. Adaptation to these changes through natural selection led to changes in phenotype, and variation that is still visible in present-day populations. Ancient DNA allows us to see the genetic change through time underlying this adaptation, and thus to observe human evolution directly.

We use genome-wide data from over four hundred ancient Europeans, dating from 12,000 to 1,500 BCE, to determine which parts of the genome were under selection in this time period. We show that genes involved in immunity, pigmentation, and metabolism were under the strongest selection, although with selection coefficients generally less than 1%. We also show that polygenic traits – in particular height and other anthropometric traits – were strongly selected, explaining much of the variation across Europe today. Interestingly, we also show that, while many of the variants under selection are very ancient, the specific combinations of phenotypes commonly associated with Europeans today are relatively recent–in most cases dating back only a few thousand years. More generally, we show that most strong selection acted on pre-existing variation rather than de novo mutations, and that much of the variation that was adaptive in Europe was also adaptive in other parts of the world.

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