Study explains why human brains is three times larger than simians

studies carried out on the genes of a human and a chimpanzee provide a clue to why our brains are three times larger than those of our closest relatives.

The studies were conducted by an international team of scientists led by David Haussler of the University of California, Santa Cruz, in the us. They showed that a gene active during a critical stage in brain development seems to have evolved faster in humans than in chimps. While the precise function of the gene is not yet known, the group suggests that it plays a role in the development of the cerebral cortex, the part of brain which controls functions such as information processing and language skill. The study was published in the online version of Nature.

The group used a computer model to compare the genomes of a series of vertebrates including humans, chimpanzees and chicken. The data showed 49 rapidly evolving regions in the human genome, which were named human accelerated regions (har).

Further studies on one of these regions, har1, revealed that it was part of two overlapping genes that are active during embryonic development. There were only two differences in the gene in chicken and chimp. But the same region in humans had changed markedly in the 6 million years since humans and chimps diverged from a common ancestor. "We found 18 differences between chimps and humans, which is an incredible amount of change to have happened in a few million years," says Katherine Pollard, one of the researchers. The group now plans to study the remaining 48 regions.

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