Calling someone a Neanderthal might actually be a compliment, according to a new study from researchers at the U of C and the Howard Hughes Medical Institute (HHMI).

The study, which appeared in the November 7 edition of the Proceedings of the National Academy of Sciences, provides evidence that a gene coding for superior brain development may have been first passed to modern humans (Homo sapiens) by Neanderthals (Homo neanderthalensis).

The researchers looked at a gene known as microcephalin. “Microcephalin controls brain size during development,” said Bruce Lahn, one of the study’s authors, in an e-mail interview. “When the function of this gene is disrupted by a severe mutation, the affected person will have a brain that is about a third of the normal size.”

Lahn is a Howard Hughes Medical Institute researcher and a professor in the Department of Human Genetics at the University.

Prior research on this gene showed that a specific variant of it, known as the D allele, first appeared in Homo sapiens about 37,000 years ago. Today, the D allele accounts for about 70 percent of all microcephalin genes worldwide. This rapid rise in frequency made the researchers suspect that it gave humans some kind of evolutionary advantage.

“We don’t know yet what this advantage is…but we speculate that it might alter brain function in some way,” Lahn said.

Further research on the D allele showed that it differed from other variants of the gene by a large number of mutations, indicating it likely rose from a genetic lineage different from that of modern humans. The researchers estimate this lineage broke off from humans about one million years ago, but the D allele was somehow introduced into Homo sapiens 37,000 years ago.

The team suspects interbreeding between humans and Neanderthals is the source. “Given that humans and Neanderthals coexisted in many parts of the world 30,000-50,000 years ago, a likely candidate for the origin of the D allele is obviously Neanderthals,” Lahn said.

Because little of the human gene pool seems to have come from Neanderthals, this interbreeding probably was not common. But Lahn says it is hard to put a number on just how many times it happened.

“My guess is it is more than just a few hanky panky trysts,” he said.

Lahn now plans to look for other genes that may have come to modern humans from Neanderthals or other lineages. His discoveries could have a big impact on how humans view themselves in the grand evolutionary scheme.

“Our finding shows that some of the archaic Homo species that we replaced (and which we now deem to be less worthy than us) may well still be living within our genes….In fact, they have made us a better species with their genetic gifts,” Lahn said.

The study was co-authored by Patrick Evans, Nitzan Mekel-Bobrov, and Eric Vallender, all HHMI Researchers and graduate students in the Department of Human Genetics at the U of C; and Richard Hudson, a professor in the Department of Ecology and Evolution at the U of C.