Sex with Neanderthals Made Us Stronger

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THE GIST

- The immune systems of modern humans got a boost when our early ancestors interbred with archaic species.

- Genetic analysis shows that two now-extinct species contributed to the DNA of all living people.

- In Europe and Asia, Neanderthals and Denisovans interbred with modern humans, some of whom brought the newly acquired genetic changes back to Africa.

Mating with Neanderthals and another group of extinct hominids, Denisovans, strengthened the human immune system and left behind evidence in the DNA of people today, according to new research.

The findings add to the growing body of evidence that modern humans who left Africa around 65,000 years ago mated with Neanderthals and Denisovans -- two archaic species that lived in Europe and Asia.

The study, which appears in this week's Science, is among the first to show how the interbreeding shaped modern human genes and the attributes they pass to us.

Peter Parham, a professor of cell biology, microbiology and immunology at the Stanford University School of Medicine, and his team focused their analysis on "HLA" genes, which are fast-evolving vital components of the human immune system.

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"The modern human populations who left Africa to colonize other continents were likely to have been small groups who started off with limited HLA diversity and suffered further reduction of HLA diversity due to disease," Parham told Discovery News. "Interbreeding with archaic humans introduced additional HLA variants into the modern human population that increased their genetic viability and capacity to resist infection."

He and his colleagues studied the genomes for Neanderthals and Denisovans, as well as the DNA of modern human populations. The organization Bone Marrow Donors Worldwide, as well as bone marrow registries from several countries, provided data on HLA genes.

The analysis shows that Neanderthal and Denisovan HLA genes now represent more than half of such immune system-related DNA in modern European and Asian populations. They also appear to have been later introduced into Africans.

The specific gene HLA-A, for example, is present in the Neanderthal and Denisovan genomes. It contributed this much to the following modern human populations: Up to 95.3 percent for Papua New Guineans, 80.7 percent for Japanese people, 72.2 percent for Chinese people, 51.7 percent for Europeans, and 6.7 percent for Africans.

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