Approximately 50,000 years ago, modern humans encountered Neanderthals and interbred. The consequences of these cross-species coital trysts on human populations today is starting to become clearer: Scientists believe that one to three percent of the genomes of modern Eurasians are derived from Neanderthal DNA, a genetic inheritance that’s been associated with increased depression risk, certain skin and blood conditions, and an increased likelihood of nicotine addiction.
The way those ancient genes got into our gene pool, however, wasn’t exactly straightforward.
On Friday, Vanderbilt University professor Tony Capra, Ph.D. graduate student Corrine Simonti presented unpublished research at the annual meeting of the American Society for Human Genetics showing that those ancient genes were at first lost — and later returned to the modern human gene pool.
A map of early human migration in favor of the “out of Africa” theory.
Neanderthals and humans are believed to have a shared hominin ancestor, so it’s believed that many of the gene variants in question — alternative forms of genes that are found at the same place on a chromosome, known as alleles — were once common to both Neanderthals and humans. Neanderthals continued to carry these old alleles, while the ancient humans “lost” most of them over several generations. But when Capra and Simonti analyzed the genes of “supergroups” of modern-day humans, they found one particular allele, responsible for changes in gene expression at a gene called OAS, that at first seemed to be derived from Neanderthals but was in fact an ancestral human allele that was “introgressed,” or reintroduced.