Can't Quit Smoking? Try Blaming Neanderthals

We’ve long known that humans and Neanderthals share at least some genetic material—recent estimates put it at about 2 percent—but a new  Harvard University analysis, published Wednesday in Nature, tells us exactly what we share, something that has only become possible because of new, high-quality genome sequencing. By studying the genetic variability in 846 non-African people, 176 people from sub-Saharan Africa, and the complete genome of a 50,000-year-old Neanderthal, Sriram Sankararaman and his team were able to trace certain alleles from Neanderthals into present-day humans.

The findings are utterly fascinating. The alleles that modern, non-African humans (sub-Saharan Africans are believed to share very little DNA with Neanderthals) share with Neanderthals are associated with things such as nicotine addiction, Type II diabetes, and a host of other diseases. You can't actually blame Neanderthals for your smoking—though you're certainly welcome to try—because it's rather misguided to pin complex behavior on a single gene. Still, it's fascinating to see that Neanderthal genes still show up in our DNA.

The findings also suggest that Neanderthal DNA led humans to develop stronger keratin, which is prominent in skin, hair, and nails and may have allowed early humans to survive in colder environments.

“It is tempting to think that Neanderthals were already adapted to the non-African environment and provided this genetic benefit to humans,” David Reich, one of the authors, said.

But just as interesting, perhaps, is what the researchers didn’t find. Researchers found very little Neanderthal DNA on humans’ X and Y chromosomes, suggesting that interbreeding among modern humans and Neanderthals happened near the end of our divergence.

“This suggests that when ancient humans met and mixed with Neanderthals, the two species were at the edge of biological incompatibility," Reich said.

The team also found vast stretches of human DNA that appeared to have just a small influence from Neanderthals, which may provide clues as to why they died out and we’ve survived. Those stretches may have included genes that were harmful to early humans and were naturally selected out of the gene pool.

Others have persisted to the present. But, as with most human traits, genetics doesn’t tell the whole picture. Just because Neanderthal alleles are associated with modern diseases such as diabetes doesn’t mean, for sure, that Neanderthals once suffered from the ailment.

“It’s not that these are definitely the alleles causing the phenotype (the trait), but these are alleles that are often associated with the phenotype,” Sankararaman said. “We can’t say ‘Neanderthals were smokers’ or that Neanderthal ancestry has a whole has been bad or it’s been good. A lot of these things are controlled by many genes.”

It’s still an incredible finding that tells us more about our ancestry and can, potentially, tell us more about Neanderthals. Though we can’t say for sure that your great great great half uncle Byron had a smoking problem, Sankararaman says that with more analysis, and better-quality genomes, we might be able to suggest that he might have.

It may also be possible to trace the origin of certain diseases back to Neanderthals, and that could have some relevance today. Because sub-Saharan Africans share much less DNA with Neanderthals, they may be less likely to have certain diseases. Anecdotally, there’s some research to back that up. Crohn’s Disease has a much higher incidence in people of eastern European descent, and has just recently begun to become a problem in African American populations. That correlation doesn’t hold in some other cases—African Americans have a much higher incidence of Type II diabetes than white Americans, for instance.

Knowing what genes came from where isn’t likely to have much medical relevance, at least for the time being, Sankararaman says, but it does give us insight into how humans evolved.

“We’re trying to understand how we got the phenotypes we have, and what important forces occurred that allowed us to acquire these traits,” he said. “As we get better data we’ll begin to have an even clearer picture.”