Genetic data of unprecedented completeness have been pulled from the fossil remains of a young Stone Age woman. The DNA helps illuminate the relationships among her group ancient Siberians known as Denisovans Neandertals, and humans. <\/p>\n
The Denisovans genetic library suggest that she came from a small population that expanded rapidly as it moved south through Asia, says a team led by Matthias Meyer and Svante Pbo of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany. Denisovans passed genes to Papua New Guineans but not to Asians, Europeans or South Americans, the researchers report online August 30 in Science. Thats in line with previous evidence that Denisovans contributed to the ancestry of present-day Australian aborigines and Melanesians. <\/p>\n
The new investigation also finds that Asians and South Americans possess more Neandertal genes than Europeans do. Although Neandertals inhabited Europe and West Asia, they may have interbred most frequently with Homo sapiens in East Asia, or, possibly, had their genetic contributions to Europeans diluted as increasing numbers of Stone Age humans reached that continent. <\/p>\n
We can now start to catalog essential genetic changes that occurred after we separated from our closest extinct relatives, Pbo says. Preliminary DNA comparisons between people today and the young female Denisovan have identified eight human-specific genes involved in brain functions, including one linked to language and speech development. <\/p>\n
Despite the new advance in retrieving ancient DNA, Denisovans evolutionary identity, and the full extent of Denisovan flings with human groups, is far from settled. Denisovan fossils, which date to at least 44,000 years old, consist of only a finger bone and two teeth unearthed at Siberias Denisova Cave. <\/p>\n
Previous work partly reconstructed DNA from the finger fossil and unveiled a close genetic link between Neandertals and Denisovans (SN: 1\/15\/11, p. 10). <\/p>\n
Think of the new achievement as Denisovan DNA 2.0. Meyer and Pbos group devised a method to separate the paired chromosomes, the coiled packages in which DNA is stored and inherited, in ancient samples. DNA inevitably degrades over the millennia, but preserved stretches on one chromosome often compensate for damaged patches on a corresponding chromosome. This allowed scientists to read the DNA letters of nondegraded sections of the complete genetic file. Going over each stretch of DNA 30 times, the researchers were able to assemble a version of Denisovan DNA thats about as complete and accurate as what can be obtained from a living person. <\/p>\n
Producing a full genome of such high quality from such an old specimen illustrates how far we have come in just a few years in the field of ancient DNA sequencing, says evolutionary geneticist Rasmus Nielsen of the University of California, Berkeley. <\/p>\n
Comparisons of premium-grade Denisovan DNA to large samples of DNA from people today should begin to clarify where and when ancient interbreeding took place, Nielsen says. <\/p>\n
Meyer and Pbos team compared its new-and-improved Denisovan material to genetic samples from 11 living people, including five Africans from different tribes or ethnic groups; two Europeans, one from France and one from Sardinia; two Chinese, one from a northern ethnic group and one from a southern ethnic group; a Papua New Guinean; and a villager from Brazils Amazon forest. <\/p>\n<\/p>\n
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