Dr. David Reich from Harvard Medical School and his colleagues have produced a world map of Denisovan and Neanderthal ancestry in 120 diverse populations. Their analysis proposes that Denisovan admixture into humans occurred about 100 generations after Neanderthal admixture.
Neanderthal. Image credit: Trustees of the Natural History Museum, London.
Dr. Reich and co-authors collected their data by comparing known Neanderthal and Denisovan gene sequences across more than 250 genomes from 120 non-African populations publically available through the Simons Genome Diversity Project.
The analysis was carried out by a machine-learning algorithm that could differentiate between components of both kinds of ancestral DNA, which are more similar to one another than to modern humans.
The results, published this week in the journal Current Biology, showed that individuals from Oceania possess the highest percentage of archaic ancestry and South Asians possess more Denisovan ancestry than previously believed.
This reveals previously unknown interbreeding events, particularly in relation to Denisovans.
“We developed methods that can disambiguate the locations of segments of Denisovan and Neanderthal ancestry in present-day humans and applied them to 257 high-coverage genomes from 120 diverse populations, among which were 20 individual Oceanians with high Denisovan ancestry,” the scientists explained.
“In Oceanians, the average size of Denisovan fragments is larger than Neanderthal fragments, implying a more recent average date of Denisovan admixture in the history of these populations.”
“We document more Denisovan ancestry in South Asia than is expected based on existing models of history, reflecting a previously undocumented mixture related to archaic humans.”
This map shows the proportion of the genome inferred to be Denisovan in ancestry in diverse non-Africans: the color scale is not linear to allow saturation of the high Denisovan proportions in Oceania (bright red) and better visualization of the peak of Denisovan proportion in South Asia. Image credit: Sriram Sankararaman et al.
In contrast, Western Eurasians are the non-Africans least likely to have Neanderthal or Denisovan genes.
“The interactions between modern humans and archaic humans are complex and perhaps involved multiple events,” Dr. Reich said.
_____
Sriram Sankararaman et al. The Combined Landscape of Denisovan and Neanderthal Ancestry in Present-Day Humans. Current Biology, published online March 28, 2016; doi: 10.1016/j.cub.2016.03.037
