Aug. 17, 2006 —Scientists believe they have found a key genetic change that helped the human brain evolve from our chimp-like ancestors.
In just a few million years, one area of the human genome seems to have evolved about 70 times faster than the rest of our genetic code since humans and chimps diverged from their common ancestor.
That change appears to have played a role in a rapid tripling of the size of the brain's crucial cerebral cortex, according to research published Thursday in the journal Nature.
Study co-author David Haussler, director of the Center for Biomolecular Science and Engineering at the University of California, Santa Cruz, said his team found strong but still circumstantial evidence that a certain gene, called HAR1F, may provide an important answer to the question: "What makes humans brainier than other primates?"
Looking at 49 areas of the genome that have changed the most between the human and chimpanzee genomes, Haussler zeroed in on an area with "a very dramatic change in a relatively short period of time."
That one gene didn't exist until 300 million years ago and is present only in mammals and birds, not fish or animals without backbones. But across nearly all of the animals in which it exists, that gene looks alike from one species to the next.
For example, there are only two differences in the gene between a chimp and a chicken, Haussler said.
But there are 18 differences in the gene between humans and chimps, and they all seem to have occurred in the time since humans and chimps diverged from their common ancestor, according to the researchers.
"It looks like in fact it is important in the development of brain," said co-author Sofie Salama, a research biologist at Santa Cruz who led the efforts to identify where the gene is active in the body.
Andrew Clark, a Cornell University professor molecular biology who was not part of Haussler's team, said that if true, that quickly paced genetic change would be "terrifically exciting."
However, the reported genetic change is so fast that Clark said he has a hard time believing it, unless something unusual happened in a mutation. It's not part of normal evolution, he said.
The scientists still don't know specifically what the gene does. But they know that this same gene turns on in human fetuses at seven weeks after conception and then shuts down at 19 weeks, Haussler said.
