New Map Reveals How Much Neanderthal and Denisovan Blood Is in You

March 30, 2016 | Gillian Burrell

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The legacy of these mysterious hominins is in your blood.

You may have heard that our ancestors once bred with the Neanderthals, but the mingling didn’t stop there. A lesser-known hominin group called the Denisovans also mixed with humans, and recent research shows their influence over us is stronger than previously thought.

Researchers from Harvard Medical School and UCLA conducted an in-depth analysis of the genomes of modern humans, connecting Denisovan ancestry to specific traits and abilities, including adaptations to high altitudes.

In the modern humans, up to 5 percent of the genome may be Denisovan, compared to just 2 percent from Neanderthals. In order to determine which of our genes are Denisovan, the team developed a computer algorithm which identifies segments of DNA that are characteristic of Denisovans, Neanderthals, and ancient humans.

SEE ALSO: Human-Neanderthal Interbreeding Suggests Major Evolutionary Timeline Change

According to their findings, humans bred with Denisovans about 100 generations after mixing with Neanderthals. And although the Denisovans went extinct, their legacy continues in our genomes.

"There are certain classes of genes that modern humans inherited from the archaic humans with whom they interbred, which may have helped the modern humans to adapt to the new environments in which they arrived," says senior author David Reich, in a release.

South Asians in particular have a lot of Denisovan blood. In Papua New Guineans, this ancestry likely confers a heightened sense of smell, while Tibetans benefit from the Denisovan ability to thrive at high altitudes.

Interestingly, Neanderthal and Denisovan genes are spread virtually everywhere in our genome except for the X chromosome and genes expressed in the testes. The researchers speculate there must be a good reason that we kept our human genes in these two places. Most likely, interbreeding caused a reduction in male infertility, so over the generations, evolution selected for human genes in the testes and X chromosome, and the Denisovan genes disappeared.

The authors laid out their findings in the map seen below. 250 genomes from 120 non-African populations were analyzed, and the percentage of Denisovan ancestry is indicated from low (black) to high (red). People of African ancestry were not included because interbreeding only occurred in human populations that migrated from Africa.

Sankararaman et al./Current Biology 2016

The results of the study are published in Current Biology.

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