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WASHINGTON - They may all be black and hairy and they may all eat and act in much the same way, but chimpanzees from different parts of Africa are genetically more diverse than all of humanity, researchers reported today.
Experts have long marvelled that older ideas of race
are not reflected in human DNA. Genetic diversity is more pronounced within population groups than between them, with only a few gene differences accounting for the wide variations seen in eye, skin and hair colour across humanity.
So animals all about the same size and colour and showing few behavioural differences must be even more genetically identical, right?
Wrong, says Molly Przeworski, assistant professor of human genetics at the University of Chicago.
Her team looked at the DNA of the three designated populations of chimpanzees in Africa -- the eastern, western and central populations, designated by some researchers as sub-species of the chimpanzee.
They found that a western chimpanzee has more differences, genetically, from an eastern chimp than any one human being has from another.
"It is the first genetic confirmation that they are distinct populations," Przeworski said in a telephone interview. "I stay away from the word 'subspecies'."
The study, done with experts at the Broad Institute at the Massachusetts Institute of Technology and at Arizona State University, is interesting in its own right, but also sheds light on human origins, Przeworski said.
"This gives us a working model of how human evolution might have proceeded," she said.
Millions of years ago in Africa, ancient remains indicate that several species of pre-humans emerged and lived perhaps side-by-side. Chimpanzees, the closest genetic living relative to human beings, may be undergoing changes similar to those that drove human evolution.
Przeworski's team also looked at bonobos, a separate species of chimpanzee. The chimpanzee genome differs from the bonobo genome by about 0.3 per cent, which is one-fourth the distance between humans and chimps, they found.
And yet bonobos are very different from the common chimpanzee. They are smaller, much gentler and known for their frequent sexual interactions.
The differences among the three common chimpanzee species are smaller but still significant. And they reflect geographic barriers, said Celine Becquet, a graduate student who did the analysis for Przeworski.
"We think most of this separation is genuine, a long-term consequence of geographic isolation," Becquet said.
One major barrier between the populations is the Congo River. "Chimps don't swim," Becquet said. "For them, water provides a very effective border."
Writing in the Public Library of Sciences journal PLoS Genetics, the researchers say they estimate that bonobos, which live south of the Congo River, split off from the ancestors of modern chimpanzees about 800,000 years ago.
Western chimps appear to have separated from central and eastern chimpanzees about 500,000 years ago and central and eastern chimps would have divided from one another about 250,000 years ago.
The interest is more than academic, Przeworski said, noting that all chimpanzees are a threatened species.
"It means we have to protect three separate habitats, all threatened, instead of just one," she said.
- REUTERS
