IT IS often thought of as one of the things that make humans unique. Now, researchers are uncovering the suite of genes that gave us our gift of the gab.
All of them appear to be controlled by a master-switch gene called Foxp2. When inactive, this gene causes severe speech and language problems in humans. Although other animals have versions of Foxp2, in 2002 a German team identified two small alterations in the protein the human Foxp2 produces that are not carried by our closest living relative, the chimpanzee. This suggested that the human version of Foxp2 may function differently, and be a key element in our unique linguistic abilities.
To discover what Foxp2 does differently in humans, neuroscientists and at the University of California, Los Angeles, grew human brain cells lacking Foxp2 in Petri dishes. To some they added human Foxp2 and to others the chimp version. They then recorded all the genes that were affected. Out of the hundreds of genes controlled by Foxp2, they identified 116 that responded differently to the human version of Foxp2.
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This set of genes fits well with Foxp2鈥榮 suggested role in the evolution of language and speech, says Konopka. Many control brain development or have been linked to cognition. Others are involved in controlling body movement and guiding the development of facial and laryngeal tissues that are essential for articulation.
Evolutionary studies of Foxp2 suggest it acquired its human-specific changes in the last half million years of human evolution 鈥� roughly when language is thought to have emerged. Geschwind has done preliminary studies of the evolution of the 116 genes that Foxp2 affects, which suggest they may have a similar history. 鈥淚t brings up the possibility, which is not at all remote, that these genes may have evolved in concert,鈥� he says, adding that this may even be true for other genes involved in language.
While the results hint at a central role for Foxp2 in the evolution of language, Geschwind cautions against calling it 鈥渢he language gene鈥� as some have in the past. 鈥淓ither Foxp2 itself is pretty damn important,鈥� he says, 鈥渙r it鈥檚 part of a regulatory circuit 鈥� something else is regulating Foxp2 that no one else has found yet.鈥�
Geschwind鈥檚 team carried out a second experiment, comparing patterns of gene activation in adult human and chimpanzee brain tissue. They found a striking overlap between the genes whose activity was different in the human brain tissue and the set of genes that are controlled differently by human Foxp2.
The finding is preliminary, but if confirmed, it might mean a significant part of the difference between human and chimpanzee brains could be explained by two small changes in one gene, says of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany. 鈥淭hat would be really amazing.鈥�