Analyses of ancient DNA from prehistoric humans paint a picture show of dramatic population change in Europe from 45,000 to vii,000 years ago, according to a new study led past Howard Hughes Medical Institute Investigator David Reich at Harvard Medical School.

The new genetic information, published May 2, 2016 in Nature, reveal two big changes in prehistoric human populations that are closely linked to the end of the last Ice Historic period effectually xix,000 years ago. As the ice sheet retreated, Europe was repopulated by prehistoric humans from southwest Europe (e.g., Spain). Then, in a second consequence most fourteen,000 years agone, populations from the southeast (e.g., Turkey, Greece) spread into Europe, displacing the kickoff group of humans.

Archeological studies accept shown that modern humans swept into Europe about 45,000 years ago and caused the demise of the Neanderthals, indicated past the disappearance of Neanderthal tools in the archaeological record, explained Reich. The researchers also knew that during the Ice Historic period -- a long period of time that ended nigh 12,000 years ago, with its peak intensity betwixt 25,000 and nineteen,000 years agone -- glaciers covered Scandinavia and northern Europe all the way to northern France. Equally the ice sheets retreated beginning nineteen,000 years ago, prehistoric humans spread dorsum into northern Europe.

Simply prior to this study, in that location were only iv samples of prehistoric European modern humans 45,000 to 7,000 years old for which genomic data were available, which fabricated information technology all but impossible to understand how human populations migrated or evolved during this menses. "Trying to represent this vast period of European history with just four samples is like trying to summarize a motion-picture show with four still images. With 51 samples, everything changes; we tin follow the narrative arc; we get a vivid sense of the dynamic changes over time," said Reich. "And what we see is a population history that is no less complicated than that in the last 7,000 years, with multiple episodes of population replacement and immigration on a vast and dramatic scale, at a time when the climate was changing dramatically."

The genetic data testify that, showtime 37,000 years ago, all Europeans come up from a unmarried founding population that persisted through the Water ice Age, said Reich. The founding population has some deep branches in unlike parts of Europe, one of which is represented by a specimen from Belgium. This branch seems to have been displaced in most parts of Europe 33,000 years ago, simply around xix,000 years ago, a population related to it re-expanded across Europe, Reich explained. Based on the earliest sample in which this ancestry is observed, it is plausible that this population expanded from the southwest, present-day Spain, after the Ice Age peaked.

The second event that the researchers detected happened fourteen,000 years agone. "We come across a new population turnover in Europe, and this fourth dimension it seems to be from the due east, not the west," said Reich. "We run into very different genetics spreading across Europe that displaces the people from the southwest who were there earlier. These people persisted for many thousands of years until the inflow of farming."

The researchers also detected some mixture with Neanderthals, around 45,000 years ago, as modernistic humans spread across Europe. The prehistoric homo populations contained three to six percent of Neanderthal Dna, just today nigh humans only have about two per centum. "Neanderthal DNA is slightly toxic to modern humans," explained Reich, and this written report provides evidence that natural choice is removing Neanderthal ancestry.

The study was an equal collaboration of David Reich'south laboratory with the laboratories of Svante Pääbo and Johannes Krause, which worked together to excerpt and analyze the DNA from these ancient bones. Aboriginal specimens are oftentimes contaminated with microbial Dna, as well every bit DNA from archaeologists or lab technicians who have handled the specimens.

To become around these problems, the research team used a technique called in-solution hybrid capture enrichment. The team used about 1.two million 52-base-pair Dna sequences corresponding to positions in the human genome that they were interested in equally allurement to target specific segments of Dna. Subsequently they washed the ancient Deoxyribonucleic acid over the ane.2 million probe sequences, the researchers sequenced the ancient Dna that was captured by the probes.

To eliminate contamination that may have been introduced from treatment the specimens, the researchers restricted analysis of many of the samples to sequences that had characteristic lesions of ancient DNA -- a cytosine to uracil error at the offset of the sequence. Modern Deoxyribonucleic acid typically does not have these errors, then contamination can be avoided by restricting the analysis to the sequences that do take them, said Reich.

"The ability to obtain genome-scale data from ancient basic is a new technology that's just been around for the last v or vi years," Reich emphasized. "Information technology'south a new scientific instrument that makes information technology possible to await at things that have not been looked at before."