Domingo 28 de Abril de 2002, Ip nš 13

Of chimps & men: bodies alike, minds different
As different as chimps and humans look, they're mostly identical genetically -- except for their brains.

A team of European and American researchers compared gene activity in the brains, liver and blood of chimpanzees and humans. They found that the two share about 98.7 percent of the same genes and have very similar body tissues.

But human brains have about five times more genetic activity, according to the study appearing Friday in the journal Science.

"There were many genetic changes that occurred on the way to developing humans," said Dr. Ajit Varki, a professor of medicine at the University of California, San Diego, and co-author of the study. "This study suggests that changes in the brain were one of the main ways that humans evolved away from chimps."

"There are many people who have spoken out about the differences, but they have really oversimplified things," said Dr. Elaine V. Muchmore, a researcher at the Veterans Affairs San Diego Healthcare System and a UCSD professor of medicine.

"The human brain is a very, very complicated organ and this study validates that," said Muchmore, a co-author of the study.

Chimpanzees are more closely related to humans than any other primate. The two are thought to have shared a common ancestor five to seven million years ago, although just what that ancient primate looked like is unknown. Since then, chimps and humans have evolved separately, with humans developing a brain about twice the size of a chimp's brain, said Varki.

The study also examined gene activity in the liver, brain and blood of the orangutan, which is another type of ape like the chimp, and the rhesus macaque monkey. The researchers found that although the chimp's tissue and blood resembled that of humans, the gene activity in the animal's brain was more like that of the monkey.

"If you look at the blood of the chimp and the human, it is very hard to tell them apart," said Varki, a blood expert. "Humans are expressing more gene differences in the brain, and that is what enables us to do what we can do."

Monkeys, humans and chimps are thought to have had a common ancestor about 13 million years ago, Varki said.

The researcher said the genetic comparison of chimps and humans might lead to better therapies for human disease.

"With an understanding of the differences between humans and chimpanzees, we may be able to learn more about the genetics underlying diseases that harm humans, but not chimpanzees," said Varki.

He noted that chimps can become infected with HIV, the AIDS virus, and never get sick. They also suffer no ill effects from an infection by Plasmodium falciparum, the most serious form of malaria and a fatal disease for thousands of humans each year.

Varki said that by searching for an explanation for this different response to disease, researchers may find genes that protect the chimp but are missing in humans. This could lead, perhaps, to new cures, he said.

But Varki said the research does not mean that chimps should be turned into laboratory animals. He said that chimps are so closely related to humans that he believes "research on chimps should follow the same principles as research on humans."

Mark D. Shriver, a University of Pennsylvania researcher into early human history, said the study found "the pattern you would expect" when comparing chimps and humans. But he said that for the findings to be definitive, the researchers need to study gene activity in more tissues from all the species.

Dr. Maynard Olson, a gene researcher at the University of Washington in Seattle, said that the human-chimp study "is a start," but that much more work needs to be done.

"The problem of developing an understanding of the molecular differences between humans and chimpanzees is both a fascinating and an enormous one," said Olson.

The senior author of the paper is Svante Paabo, while the first authors are Wolfgang Enard and Philipp Khaltovich, all of the Max Planck Institute in Leipzig, Germany. There are also two co-authors from institutes in the Netherlands.


  12/04/2002. CNN.