New Historian

Ancient DNA Provides an Evolutionary Roadmap

Wheat Field in Ile de France

<![CDATA[In the first study of its nature, scientists have found genetic evidence – through the analysis of ancient DNA - connecting the arrival of agriculture in Europe approximately 8,500-years ago with widespread genetic changes to the DNA of people living at the time; altering their immune system, digestion, skin color and height. The finding secures the agricultural revolution’s distinction as one of the most profound events in all of human history. Researchers had previously found unconnected clues relating to these alterations while studying the genes of living Europeans, but the new study makes it possible to see the changes as they occurred over thousands of years. According to Rasmus Nielsen, a geneticist with the University of California, Berkeley, who was not directly involved in the recent study, scientists have been trying for decades to find out what happened in the past – and now there’s a figurative time machine. Prior to this study of ancient DNA, scientists had to rely primarily on bones or other physical remains from early humans in order to understand European history. In Europe, researchers have determined that the earliest human bones date to approximately 45,000 years ago. Early Europeans survived as hunter-gatherers for more than 35,000 years. It was only around 8,500 years ago that farmers left their first archaeological mark in the history of the continent. Scientists had already uncovered evidence which suggested the ancestors of living Europeans adapted to agriculture by natural selection. With DNA sequencing tools becoming more advanced and more available scientist were even able to find some of the traits' molecular underpinnings. But what these studies couldn’t do was determine when the changes occurred with any precision, or whether they were the result of the migration of people into Europe or natural selection. Scientists can now tackle these questions directly, thanks to the quickly growing supply of DNA supplied by ancient skeletons. It’s already been determined that the average European’s DNA comes typically from three sources. Before agriculture took hold, Europeans were a population of hunter-gatherers; next came a wave of people with DNA similar to residents of the Near East (it was likely these people who introduced agriculture to Europe). Finally, a nomadic population from Russia known as the Yamnaya swept across Europe 4,500 years ago. Evidence of these migrations was found after the analysis of dozens of ancient European genomes. In the new study the international team of experts analyzed the genomes of 230 people who were alive between 2,300 and 8,500 years ago. The huge sample size has given researchers the data needed to track distinct genetic variations as they became more common or less common throughout ancient Europe’s history. By comparing the ancient and living human genes scientists have confirmed previous hypotheses founded on living Europeans, but they have also revealed the other genes that evolved as well. Earlier studies indicated that once Europeans began raising cattle they became better at digesting milk, the new study has confirmed that the presence of a gene that aids in milk digestion (LCT) became much more common. Surprisingly it was determined this change didn’t occur with the advent of farming, because this change dates back only 4,000 years. Agriculture benefited people by providing a new source of protein; however a diet dependent on grains also created the risk of not getting enough other key nutrients. So along came the gene SLC22A4 which works on the surface of a cell to increase absorption, thereby increasing a person’s chance of survival. An indirect consequence of this genetic fix is the raised risk of digestive disorders. Changes to the color of European skin have also been tracked. The original hunter-gatherers were descendants of people from Africa and the farmers who arrived next were lighter skinned and it’s this latter trait which spread throughout Europe – helped along by the later appearance of an additional gene variant that lightened skin even further. But why? It was a long held belief that at higher latitudes light skin would capture additional vitamin D from sunlight; but early hunter-gatherers got along fine with dark skin. The new hypothesis proposes it was the move to agriculture which caused a reduction in Vitamin D intake that led to the change. Another puzzle the collection of ancient DNA addresses is the evolution of height in Europe. After combing through 169 height related genes they discovered that the early famers were relatively tall, and the Yamnaya were even taller. People living in northern Europe then inherited more Yamnaya DNA – making them taller. It’s not apparent why nature favored a shorter stature in the south but it’s clear this genetic history still affects the differences in height across the continent even now. Image courtesy of Wikimedia Commons user: Myrabella ]]>

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