Scientists Find What Separates Man, Chimps
April 11, 2002 — -- What makes us human?
While some might turn to theology to ponder the possibilities, biologists have turned to our closest "cousin," the chimpanzee, and looked for genetic differences. New analysis finds that what sets us apart may lie more in how active our genes are, rather than in actual differences in our genetic makeups. And the biggest contrasts are found in our brains.
"It's not just one or two big differences — it's multiple ones," said Elaine Muchmore, a genetic researcher with VA San Diego Healthcare System and a professor of medicine at the University of California at San Diego. "I think this underscores how complex our differences are."
The finding could help in developing treatments for AIDS, Alzheimer's and malaria, since chimpanzees are less vulnerable to symptoms of these diseases than people.
Since the 1970s, scientists have known that chimpanzees and people share about 98.7 percent of their genes. But while the genes may be identical, the amount of work they do is not always the same — particularly in the brain.
Genes provide the blueprint for all activity and development in the body, but they require messengers in the form of RNA, a molecule that carries information, and proteins to activate their coding.
The researchers used devices known as gene chips to compare the level of activity of these genetic messengers and proteins in blood and liver samples of chimpanzees and humans and then in brain samples from both. (Samples were collected from chimpanzees and humans who had died of natural causes.)
They found that the level of genetic activity was not that different in the liver and blood samples. But in the brain, it was about five times higher.
"This supports the fact that the human brain has undergone some radical evolution," said Ajit Varki, a professor of medicine at the University of California, San Diego.
Svante Paabo of the Max Planck Institute in Leipzig, Germany, was the senior author of the study, which is appearing in this week's issue of the journal Science. Varki and Muchmore, as well as Wolfgang Enard and Philipp Khaltovich of the Max Planck Institute and researchers from the Netherlands, also contributed.
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