I was home for lunch and realized this was getting TV news “coverage”. Figured I’d better post something closer to reality.

“Our studies indicate that the trend that is the defining characteristic of human evolution–the growth of brain size and complexity–is likely still going on,” said lead researcher for both papers Bruce Lahn, PhD, assistant professor of human genetics at the University of Chicago and an investigator at the Howard Hughes Medical Institute. “Meanwhile, our environment and the skills we need to survive in it are changing faster then we ever imagined. I would expect the human brain, which has done well by us so far, will continue to adapt to those changes.”

Evolution, Lahn said, doesn’t occur at the species level. Rather, some individuals first acquire a specific genetic mutation; and because that variant confers on those who bear it a greater likelihood of survival, it then spreads in the population. “We’re seeing two examples of such a spread in progress,” he said. “In each case, it’s a spread of a new genetic variant in a gene that controls brain size. This variant is clearly favored by natural selection.”

In the two Science papers, the researchers looked at variations of microcephalin and ASPM within modern humans. They found evidence that the two genes have continued to evolve. For each gene, one class of variants has arisen recently and has been spreading rapidly because it is favored by selection. For microcephalin, the new variant class emerged about 37,000 years ago and now shows up in about 70 percent of present-day humans. For ASPM, the new variant class arose about 5,800 years ago and now shows up in approximately 30 percent of today’s humans. These time windows are extraordinarily short in evolutionary terms, indicating that the new variants were subject to very intense selection pressure that drove up their frequencies in a very brief period of time–both well after the emergence of modern humans about 200,000 years ago.

Each variant emerged around the same time as the advent of “cultural” behaviors. The microcephalin variant appears along with the emergence of such traits as art and music, religious practices, and sophisticated tool-making techniques–which date back to about 50,000 years ago. The ASPM variant coincides with the oldest-known civilization, Mesopotamia, which dates back to 7000 BC. “Microcephalin,” the authors wrote in one of the papers, “has continued its trend of adaptive evolution beyond the emergence of anatomically modern humans. If selection indeed acted on a brain-related phenotype, there could be several possibilities, including brain size, cognition, personality, motor control or susceptibility to neurological/psychiatric diseases.”

“The next step is to find out what biological difference imparted by this genetic difference causes selection to favor that variation over the others,” Lahn said.

The article is adapted from the original press release from UC here.