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Scientists Complete Genetic Map of the Chimpanzee

The chimpanzee Clint's genome sequence was determined by scientists. Comparatively, it is almost 99 percent identical to that of humans.
The chimpanzee Clint's genome sequence was determined by scientists. Comparatively, it is almost 99 percent identical to that of humans. (Yerkes National Primate Research Center)

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By Rick Weiss
Washington Post Staff Writer
Thursday, September 1, 2005

Scientists said yesterday that they have determined the precise order of the 3 billion bits of genetic code that carry the instructions for making a chimpanzee, humankind's closest cousin.

The fresh unraveling of chimpanzee DNA allows an unprecedented gene-to-gene comparison with the human genome, mapped in 2001, and makes plain the evolutionary processes through which chimps and humans arose from a common ancestor about 6 million years ago.

By placing the two codes alongside each other, scientists identified all 40 million molecular changes that today separate the two species and pinpointed the mere 250,000 that seem most responsible for the difference between chimpness and humanness.

"Now we can peek into evolution's lab notebook to see what went on there," said Francis S. Collins, director of the National Human Genome Research Institute, which funded the $25 million effort at 18 institutions in five countries.

On a practical level, researchers said, the work is likely to explain why chimps are resistant to several human diseases such as AIDS, hepatitis, malaria and Alzheimer's disease -- information that could lead to new ways to prevent or treat many human ills.

More profoundly, however, the achievement promises to help answer the alluring but loaded question of what, exactly, makes us truly human.

But the answer will not come easily.

"We're not going to stand up and say that these 14 things make us human," said Eric S. Lander of the Broad Institute of MIT and Harvard in Cambridge, Mass., which along with Washington University in St. Louis led the chimpanzee genome sequencing effort. "But it's not trivial to be able to say, 'Here is an inventory of the most important differences, and now go at it and figure out which of these differences contain the signatures of what is distinctively human.' "

As predicted by preliminary studies, the human and chimpanzee genetic codes are essentially 99 percent identical, a testament to how fundamentally similar the two species remain. At the same time, it is powerful evidence that seemingly modest changes in molecular code can lead to very different stations in the web of life.

Because of that 1 percent difference, experts noted, humans now dominate every ecosystem on Earth while chimpanzees and other great apes -- a group that also includes bonobos, gorillas and orangutans -- are at risk of becoming extinct within the next few decades, largely because of human activities.

Well aware of that awkward reality, several scientists yesterday used the occasion of the chimp genome's unveiling to focus attention on the creatures' plight, calling for renewed conservation efforts and new rules governing the use of great apes in research.

"There is a deep irony in the fact that the sequencing of the chimpanzee genome coincides with the potential demise of great apes in the wild," wrote Ajit Varki of the University of California at San Diego, and colleagues, in a commentary accompanying the main research report in today's issue of the journal Nature.


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