How our genomes are affected by adaptation and selection
The three major migrations that have taken place in Eurasia since the last Ice Age have affected the risk of people alive today developing a range of serious diseases. But also things like our ability to digest milk and how tall we get.
Is it possible to find out how environmental and cultural changes from the last Ice Age to the present day, through natural selection, have influenced the DNA of today’s inhabitants of Eurasia? For example, why do Scandinavians grow taller than Southern Europeans? And when did we start being able to digest dairy products and survive on vegetables? These are just a few of the questions that a large genetic study of archaeological remains from our ancestors provides answers to.
The study titled The Selection Landscape and Genetic Legacy of Ancient Eurasians, one of four articles recently published in Nature, is based on data from 1,664 archaeological skeletal remains (the oldest from the Mesolithic, and the youngest from about 1,000 years BCE), which were compared to more than 400,000 DNA profiles from modern Europeans.
The prehistoric skeletons originate from an area of Europe and western Asia that was divided along an east-west axis from Lake Baikal to the Atlantic coast, and a north-south axis from Scandinavia to the Middle East.
Ability to digest milk
One of the findings concerns the development of lactose tolerance in adults, i.e. the ability to digest this sugar in dairy products into adulthood. This ability began to emerge in the Neolithic farming communities in Europe about 6,000 years ago, but did not become dominant until much later, the study shows.
Another nutritional advantage – the ability to turn short-chain fatty acids into long-chain fatty acids, which increases our ability to survive on a vegetable diet – turned out to have a different evolutionary history in Europe than previously thought. The people that migrated to Europe during the Neolithic had already developed that ability genetically by the time they arrived.
Genetic dominance in some areas
None of the waves of migration to Eurasia that occurred during the Stone Age and Bronze Age show genetic dominance throughout this entire vast area. Instead, each wave of migration retained genetic dominance in some geographical areas but significantly less dominance in other parts of Eurasia.
This means that in today’s generations of Scandinavians, the greatest genetic influence comes from hunter-gatherers in western Europe in what are now the Baltic countries, Belarus, Poland and Russia, while genetic traces from the Anatolian farmers who migrated to present-day Scandinavia in the Neolithic period are now most clearly visible in the gene pool of people from southern Europe and North Africa.
When it comes to the ‘steppe genetics’ from the Corded Ware culture people, who took over Scandinavia from the farmers from Anatolia about 5,000 years ago, the situation is almost reversed. In Scandinavia, Yamnaya genes are strong while they are significantly weaker in southern Europe.
Scandinavians’ forefathers influence their risk of diseases
The study also deals with several physical characteristics of contemporary humans, seen in relation to the impression made on their DNA by these waves of migration. For example, the analyses show that Scandinavians’ height came with the Corded Ware people, who were genetically predisposed to be tall. This is believed to be the reason why northwestern Europeans are generally taller than southern Europeans.
The study also shows that the risk of developing a number of modern diseases is influenced by the amount of DNA that the individual has from the three major migration waves that took place after the last Ice Age.
If you have a lot of the Anatolian farmer DNA, as in southern Europe, the risk of developing bipolar disorder is greater. In Eastern Europe, where there is a high proportion of DNA from hunter-gatherers, you will instead have an increased genetic risk of developing Alzheimer’s disease and Type 2 diabetes, while northwestern Europe has the highest incidence of multiple sclerosis (MS) in the world. And the increased risk of developing MS has in fact come with the Yamnaya people.
In the future, analyses of prehistoric DNA will most likely be used to gain even more knowledge about the developmental history of mental disorders, the researchers believe.
Contact:
Kristian Kristiansen, Phone: +46(0)704-18 57 67, e-mail: kristian.kristiansen@archaeology.gu.se
Four articles in Nature
Population Genomics of Postglacial Western Eurasia (Allentoft et al.)
The Selection Landscape and Genetic Legacy of Ancient Eurasians (Irving-Pease et al.)
100 Ancient Genomes Show Repeated Population Turnovers in Neolithic Age Denmark (Allentoft et al.)
Two of the articles in Nature are related to the RISE II research project, which is financed by the Bank of Sweden Tercentenary Foundation (RJ) and is a collaboration between the Department of Historical Studies at the University of Gothenburg, the University of Copenhagen, and the Lundbeck Foundation GeoGenetics Centre. The other two articles in Nature on the Stone Age use material from the long-standing collaboration between the University of Gothenburg and the University of Copenhagen in the research projects RISE I and RISE II. This was a collaboration that began in 2011.
