By Tina Hesman Saey, Science News
Silver-tongued humans may owe their language prowess to a foxy friend. A new study provides more evidence that the human version of a protein known as FOXP2 may have aided the evolution of language.
Chimpanzees and many other animals have FOXP2, but the human version differs at two links in the chain of amino acids that make up the protein. Scientists have suspected that those two amino acid changes were not merely cosmetic, but might alter the way FOXP2 functions, perhaps paving the way for the evolution of language. The new study finds that human FOXP2, compared with the chimp version, alters the activity of at least 116 genes in brain cells grown in laboratory dishes, neurogeneticist Daniel Geschwind of the University of California, Los Angeles and colleagues report in the Nov. 12 Nature.
Of the affected genes, 61 showed higher activity with human FOXP2 than the chimp form. Many of those genes are involved in neural development and the production of collagen, cartilage and soft tissues. Those results suggest that the protein may play roles in shaping both the brain and the vocal apparatus that makes speech possible. The human version of the protein decreased activity of 55 genes.
Together these findings are "consistent with these genes being part of a molecular circuit related to human cognition," including circuits needed for language, Geschwind says. He thinks FOXP2 and the genes it regulates make the brain better able to integrate sensory information with movements, as in hearing sounds and then shaping the tongue, lips and vocal tract to reproduce those sounds.
Genes regulated by FOXP2 make up a subset of all the genes known to have different levels of activity in the brains of humans and chimps. The protein and the genes it influences account for about 20 percent of the changes in gene activity seen between the two species, the researchers discovered.
"That tells us that FOXP2 is itself responsible for many of the changes," between humans and chimps, "or that it's part of a larger circuitry," Geschwind says. "There are likely to be many things that make us human, but some of these data really highlight its importance."
FOXP2 has become a celebrity gene for its possible role in language development (SN Online: 11/5/08), but while it may help shape the neural circuits that enable speech, it's certainly not the whole story, says Pasko Rakic, a neuroscientist at Yale University.
"Change two amino acids and suddenly we speak? It's not so," he says. The new study does show important functional differences between the human and chimp versions of the protein, and may lead to a better understanding of the molecular basis of language evolution, he says.
Another caveat to the study is that the experiments were done in cells grown in laboratory dishes, says Simon Fisher, a neuroscientist at the University of Oxford in England.
"We are still some way off from describing how differences in FOXP2 alter the properties and behavior of neurons in the living brain," he says.