Researchers have identified a gene that has changed rapidly during human evolution — a discovery that could be a step towards understanding what sets us apart from other animals.

The work, reported online this week in Nature, is some of the first to come from comparing the human genome with that of the chimpanzee, which was published last September. The gene, called HAR1F, does not directly code for a protein. Instead, it lies in a non-coding segment of the genome and produces RNA. Many geneticists believe that rapidly evolving non-coding regions harbour the secret of what makes humans different from our nearest primate relatives.

HAR1F is produced by cells in the brain called Cajal–Retzius cells, which regulate how the six layers of the cortex are laid down during development. The gene may interact with a protein called reelin, which plays a vital role in this layering. “But it's wild speculation,” says geneticist David Haussler of the University of California, Santa Cruz, who led the study.

The group identified the gene by comparing the human genome with those of the chimpanzee, mouse and rat. Forty-nine segments, dubbed 'human accelerated regions' or HARs, showed sequence changes in the human version but not in the other animals. The greatest change was found in HAR1, which in humans had undergone 18 substitutions in comparison with the other animals when one or none was expected (D. Haussler et al. Nature doi:10.1038/nature05113; 200610.1038/nature05113).

What the gene does is a mystery, but there are some guesses. “Given that it's changed so dramatically only for humans, it might be involved in human-specific brain wiring,” says Gerton Lunter at the University of Oxford, UK.

One thing is becoming clear: protein-coding genes may not be the movers and shakers of human evolution scientists once thought. “We should stop looking at proteins and start looking at non-coding DNA,” says Lunter. “Everything points in that direction.”