Human-Neanderthal sex protected us from disease

You know what they say: another year, another contribution to the preponderance of scientific evidence that humans had a lot of sex with Neanderthals.

A new study by David Enard, assistant professor at the University of Arizona Ecology and Evolutionary Biology Department, and Dmitri Petrov, the Michelle and Kevin Douglas Professor of Biology at Stanford University, suggests that this interaction may have played a key role in humans not dying from a Neanderthal cold back in the day.

Enard and Petrov looked at the parts of the human genome that have to do with defense against pathogens, and compared these stretches with that of the Neanderthal genome. They found that there was a similarity, suggesting that Neanderthal DNA plays a part in our modern genetic foundation for immunity.

The close contact between Neanderthals and humans at at least two points in history, Enard and Petrov claim, meant that Neanderthals and humans passed between them their species-specific viruses. Luckily for us, human and Neanderthal genetic interaction in the form of procreation also probably passed along the alleles needed for better immunity. The protection, and the evolutionary positive selection that that affords, also answers the question of why humans may have retained some Neanderthal DNA into the modern era.

Neanderthals and humans diverged genetically around 500,000 to 800,000 years ago. Human contact with Neanderthals around B.C. 70,000 in Eurasia left genetic evidence of Neanderthal DNA in most humans not of African descent. This study adds a building block to the ways that this DNA might affect human development to this day.

Viruses are more important in shaping genetics than you might think. These Neanderthal viruses, and whether or not people had immunity passed on from the Neanderthals, decided which humans that came in contact with Neanderthals and their pathogens would survive to pass on their genes through positive selection.

The "poison-antidote" theory, or the theory that Neanderthals and humans were able to survive exposure to new pathogen exposure through intermingling had been theorized, but this study provides "preliminary evidence" that this theory might have indeed transpired. The authors suggest that 32 percent of Asians and 25 percent of Europeans might have been genetically affected by this positive selection.

Enard, in and interview with Science Daily, marveled at the discoveries that can be made by delving into DNA. "You can think of these genetic adaptations like footprints from long-extinct dinosaurs preserved in fossilized mud."