Outside the Beltway

Human Brains Getting Bigger

James Joyner · Friday, September 9, 2005 · 3 comments

The human brain is evolving–getting bigger and able to handle more complex calculations–according to a recent University of Chicago study.

Human Brains Are Getting Larger, More Complex, Scientists Say (Bloomberg)

Human brains are still evolving, increasing in both size and complexity, University of Chicago geneticists said in two papers published in the journal Science. Scientists studying two genes that regulate brain size, Microcephalin and ASPM, found groups of variants, known as haplogroups, that emerged about 37,000 years ago and 5,800 years ago, according to the papers published yesterday in Science. Anatomically modern humans evolved about 200,000 years ago.

“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,” Bruce Lahn, lead researcher for both papers, said in an accompanying statement. “If our species survives for another million years or so, I would imagine that the brain by then would show significant structural differences from the human brain of today.”

For both genes, the “new” class of variants was called haplogroup D. Versions of the Microcephalin variant are found in about 70 percent of humans, and ASPM’s haplogroup D is present in about 30 percent of today’s people, according to the papers. ASPM stands for Abnormal, Spindle-like Microcephaly Associated. Mutations of either gene can cause reduced brain size.
“For each gene, one class of variants has arisen recently and has been spreading rapidly because it is favored by selection,” the University of Chicago Medical Center said in a statement accompanying the papers. “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.”

Genes Show Signs Brain Still Evolving (AP – WaPo)

The human brain may still be evolving. So suggests new research that tracked changes in two genes thought to help regulate brain growth, changes that appeared well after the rise of modern humans 200,000 years ago. That the defining feature of humans — our large brains– continued to evolve as recently as 5,800 years ago, and may be doing so today, promises to surprise the average person, if not biologists. “We, including scientists, have considered ourselves as sort of the pinnacle of evolution,” noted lead researcher Bruce Lahn, a University of Chicago geneticist whose studies appear in Friday’s edition of the journal Science. “There’s a sense we as humans have kind of peaked,” agreed Greg Wray, director of Duke University’s Center for Evolutionary Genomics. “A different way to look at is it’s almost impossible for evolution not to happen.”

Still, the findings also are controversial, because it’s far from clear what effect the genetic changes had or if they arose when Lahn’s “molecular clock” suggests _ at roughly the same time period as some cultural achievements, including written language and the development of cities.

So, when Jules said, “Look at the big brain on Brad!” he wasn’t being metaphorical.