The ability to communicate through spoken language may be the trait that best sets humans apart from other animals. Last year researchers identified the first gene implicated in the ability to speak. This week, a team shows that the human version of this gene appears to date back no more than 200,000 years--about the time that anatomically modern humans emerged. The authors argue that their findings are consistent with previous speculations that the worldwide expansion of modern humans was driven by the emergence of full-blown language abilities.
The researchers who identified the gene, called FOXP2, showed that FOXP2 mutations cause a wide range of speech and language disabilities (ScienceNOW, 3 October 2002). In collaboration with part of this team, geneticist Svante Pääbo's group at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany, set about tracing the gene's evolutionary history.
They sequenced the FOXP2 genes of several primates--chimpanzee, gorilla, orangutan, and rhesus macaque--as well as that of the mouse, and compared them to the human sequence. Since the last common ancestor of humans and mice, which lived some 70 million years ago, there have been only three changes in the protein's amino acid sequence, the team reported online in Nature on 14 August. And two of these changes have occurred in the human lineage since it split from that of chimps roughly 6 million years ago.
The team estimated how recently the human version of FOXP2 became "fixed" in human populations--that is, when all humans harbored the last amino acid substitution. Although the date cannot be pinpointed, the team concluded that the fixation was 95% likely to have occurred no more than 120,000 years ago, and virtually certain to have occurred no earlier than 200,000 years ago. And statistical tests further indicated that the gene has been favored by natural selection.
Many researchers agree that the authors make a strong argument that the human version of FOXP2 conferred an evolutionary advantage. But many question the dating of the gene. "Dating analyses [such as these] are fraught with uncertainty," says geneticist David Goldstein of University College London, adding that "speculation that the spread of anatomically modern humans was driven by the evolution of language remains just speculation." Indeed, Pääbo suggests that this gene, which may be implicated in the ability to make the mouth and facial movements essential to speech, might have been selected for precisely because it improved vocal communication once language had already evolved.