By Justin Gillis
Washington Post Staff Writer
Thursday, August 15, 2002; Page A13

Two critical mutations appeared roughly 200,000 years ago in a gene linked to language, then swept through the population at roughly the same time anatomically modern humans began to dominate the planet, according to new research.

The findings, released online yesterday and due for publication soon in the journal Nature, provide the most compelling evidence to date that the gene, which researchers described in detail only last year, may have played a central role in the development of modern humans' ability to speak. Researchers said that could have given them a critical advantage that allowed them to supplant more primitive rivals.

A mounting body of research suggests that the mutant gene conferred on human ancestors a finer degree of control over muscles of the mouth and throat, possibly giving those ancestors a rich new palette of sounds that could serve as the foundation of language.

"It's a very exciting discovery," said Steven Pinker, a top language expert at the Massachusetts Institute of Technology. "This could be a watershed, because now that the technique has been successfully used, we can apply it to other genes with psychological effects. I think it opens the door for a new field of study."

The research indicates the genetic mutations may at least partly explain why humans can speak and animals cannot. Researchers are likely to try to introduce the genetic mutations into mice as part of their work, but they said many other genetic changes would likely be necessary to produce a talking animal, and several said they doubted anything of the sort would ever be possible, let alone desirable.

The new research was led by Svante Paabo at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany. He and his colleagues were careful not to claim in their paper that they had identified the key molecular event in the birth of human culture. But the paper added fresh evidence to the notion that they have identified at least one of the keys.

"It's very hard to prove these things," said Faraneh Vargha-Khadem, a researcher at the Institute of Child Health in London who has collaborated with the German researchers on related work but played no role in the new paper. "But it's not too far a leap to be making to say that civilizations gradually emerged from this type of ability."

Researchers don't know exactly what role the gene, known as FOXP2, plays in the body, but all mammals have versions of the gene, suggesting that it serves one or more crucial functions, possibly in fetal brain development.

The new paper demonstrates that the human version of the gene, in its critical segments, differs by only three molecules, out of 715, from the version carried by mice and by just two molecules from the version carried by chimpanzees.

That may sound minuscule, but even such tiny mutations can have profound consequences. Genes encode instructions for making proteins, the gears and levers that do all the work in biology. In this case, the mutations in FOXP2 apparently changed the shape of the relevant protein in a way that somehow permitted greater complexity in the parts of the brain controlling movement of the face, throat and voice box.

Scientists located the gene by studying 16 people in Britain, including 15 members of one large family, who have profound speech defects. It turned out all of them had inherited a defective version of the FOXP2 gene, pointing to a critical role in speech for the normal version.

The Nature paper reports several lines of evidence suggesting that the FOXP2 mutations that distinguish humans from chimpanzees occurred quite recently in evolution -- and then spread rapidly, entirely replacing more primitive versions of the gene within 500 to 1,000 human generations, or 10,000 to 20,000 years.

A sweep that rapid indicates to biologists that the new version of the gene must have conferred a significant evolutionary advantage on the human ancestors lucky enough to inherit it.

Mutations in genes happen all the time in nature, simply because the cellular machinery that copies them is not perfect. Most mutations are harmful or neutral, but occasionally a beneficial one will occur by chance -- and spread through a population because it confers an evolutionary advantage.

The German researchers said the timing of the FOXP2 mutations matches up, roughly, with anthropological evidence suggesting that fully modern humans appeared about 200,000 years ago, then spread rapidly across the planet, supplanting all proto-human ancestors.

Suggestive as the timing may be, the researchers still don't know what other genes played critical roles in the development of language, much less the relative contribution of each. "Many, many genes are going to be involved," Vargha-Khadem said.

The next logical step for the researchers is to create a research animal, probably a mouse, that carries the human mutations in FOXP2 -- then analyze the animal to see how its brain and behavior are altered. Mice presumably lack many other prerequisites for speech, but still, certain alterations of brain structure in a mutant mouse might lend support to the notion that FOXP2 is an important language gene in humans.

"If the mouse talks, then the circumstantial evidence will be pretty good," joked Wolfgang Enard, the Leipzig graduate student who is lead author on the new Nature paper. "It's unlikely, I would say."