nature science update
updated at midnight GMTtoday is friday, december 12
Genome scan shows human-chimp differences
Variations hint at how our lifestyle is reflected in our genes.
12 December 2003
The human and chimp genomes are about 99.2% identical.
Genes involved in smell and hearing are significantly different between humans and chimpanzees, researchers have discovered. The finding could be a starting point for understanding what separates us from our closest relative.
"This tells us the types of genes that are important for our differences," says Michele Cargill of the biotech company behind the comparison, Celera Diagnostics in Alameda, California. But the list does not tell us what makes us human, she cautions: "Just finding a change in one protein gives us no idea of how it affects the whole animal."
The human and chimp genomes are about 99.2% identical. In the most important bits of the genome, this figure rises to 99.5%. Yet Cargill and her colleagues believe that they have seen the fingerprint of evolution in these small DNA differences.
The researchers compared the sequences for more than 7,500 human, chimpanzee and mouse genes, compiled by the genome projects for each species. Matching the two primates against the mouse revealed whether chimp or man has changed most from the ancestral starting point shared by the three mammals.
All DNA sequences change over time as mutations build up. To spot the effects of evolution, the researchers looked for genes that had altered more during the five million years since human and chimpanzee split than would be expected by chance. About 1,500 genes seem to have been affected by selection, this analysis showed.
"It's the first genome-wide comparison of humans and chimps," says geneticist Svante Paabo of the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany. "It will allow us to form many interesting hypotheses about the crucial new features during human evolution."
But some scientists doubt that the differences studied are the work of evolution. There are so few changes between human and chimpanzees, argues evolutionary biologist Adam Eyre-Walker, that comparing single genes gives hardly anything to analyse.
"My gut feeling is that there aren't enough data here," says Eyre-Walker, who works at the University of Sussex, UK. He feels that it would be better to combine information from many genes.
Of those human genes that have a known function - about half the total - nearly 50 are linked to smell. Many of them seem to be decaying into uselessness, probably reflecting the lesser importance of smell in our lifestyle relative to that of chimpanzees.
People will now analyse hearing in apes with greater interest
Max Planck Institute
The team also found changes in 21 human genes that are linked to hearing. "It is tantalizing to speculate that this could have to do with language," says Paabo. "People will now analyse hearing in apes with greater interest."
Nearly 80 genes used to digest proteins also differ between chimps and humans - perhaps reflecting how the human diet has changed in the five million years since we split from our cousins. Many of the differing genes are associated with disease. Mutations in a gene called tectorin-alpha, for example, cause deafness in humans.
# Clark, A. G. et al. Inferring nonneutral evolution from human-chimp-mouse orthologous gene trios. Science, 302, 1960 - 1963, (2003). |Homepage|© Nature News Service / Macmillan Magazines Ltd 2003