Ceilidh

Michael Zey
futurist3000@aol.com

-- Scientists comparing genes from chimpanzees to those of humans and mice have discovered some of the genes that make humans so different from other animals.

In the December issue of Science, researchers report finding differences in the gene sequences between humans and chimps that may provide clues to the genes responsible for such important factors in human evolution as the ability to speak and understand language and to walk upright.

"Despite the fact that humans and chimps are so similar, we can still find evidence of differences in coding sequences and see what kind of genes evolution acts on," says one of the study's authors, Michele Cargill.

Cargill, manager of integrated genomic applications at Celera Diagnostics in Alameda, Calif., says humans and chimps share nearly 99 percent of their gene sequences.

For this study, Cargill and her colleagues looked at 7,645 gene sequences in chimps and compared them to their related genes in humans and in mice. Cargill says they looked for small differences in the gene sequences.

The researchers then further studied these genes to determine which had changed randomly, and which had mutated because of positive selection. When a gene changes through positive selection, that means some evolutionary benefit occurs as a result of the mutation.

"We found around 1,500 genes that looked like they might be important in making humans humans," says Cargill.

For example, the researchers found several genes that are involved in the development of hearing in humans that seemed to have evolved quickly, which the authors suggest may have been necessary to process speech sounds. When one of these genes is damaged in humans, it causes deafness, according to Cargill.

Other genes that looked like they had undergone positive selection were some responsible for the development of the skeletal system, which Cargill says is obviously quite different in humans and chimps.

Almost all of the olfactory genes -- those responsible for the sense of smell -- were quite different in humans and chimps.
Additionally, Cargill says, humans have genes that chimps don't have that allow better digestion of meat and the amino acids found in meat.

"We eat more meat, and these mutations allow us to process meat and get more nutrition from it," she explains.
Cargill says it's possible that in the future, this list of genes that are uniquely human may provide researchers with a better target for researching genes that cause human disease.

Ursula Goodenough, a professor of biology at Washington University in St. Louis, says this study may indeed provide a useful database for future research. But, she notes, any practical implications from this work would likely be decades in the making.

Despite the differences in some genes, she adds, this study once again proves that "chimps are the closest creatures to us, and we have so much to learn from them."

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