The Japan Times
November 6, 1999

Chimps more varied, older than humans are

WASHINGTON (Reuters) Chimpanzees are far more genetically diverse than human beings are, researchers said Thursday, a finding that has implications both for efforts to conserve endangered chimps and for learning more about human origins.

A team of German genetic experts said their findings bolster suggestions that current human populations date back to some sort of "bottleneck" in evolution just a few hundred thousand years ago.

Henrik Kaessmann and Svante Paabo of the Max-Planck-Institute for Evolutionary Anthropology in Leipzig, Germany, compared the genes of both species of chimpanzees, as well as three subspecies.

"The results show a strikingly lower amount of variation in humans than in chimps," Paabo said in a statement.

"The simplest explanation for this is that at some rather recent point in the past, humans have been few in numbers. From a genetic point of view, this point could be the origin of modern humans."

Scientists make comparisons between humans and chimps because they are our closest cousins, sharing more than 98 percent of our DNA.

All animals have unique variations in genes from individual to individual. This variation can be meaningless, or can make a difference in, for instance, susceptibility to disease.

Writing in the journal Science, Kaessmann's team said they examined genes from the three recognized subspecies of chimps — Central African chimpanzees, western African chimpanzees and Eastern African chimpanzees.

They also looked at bonobos, commonly known as dwarf chimpanzees.

They looked at one gene called Xq13.3, which is found on the X chromosome, one of the two chromosomes related to sex. It has no known function, but it is known to have a low mutation rate and has been well studied in people.

They found Xq13.3 has almost four times as many variants and is three times as old in chimps as in humans.

This supports other studies that find humans are extremely closely related to one another genetically despite what geneticists consider to be arbitrary designations of "race."

The researchers assumed that chimpanzees and humans diverged from a common ancestor 5 million years ago, and made comparisons.

It is possible to estimate how long ago the animals in a common population had a common ancestor by looking at the rate of mutations in a gene. This is one method used to determine the age of the "ancestral Eve" from whom all humans are theoretically descended.

This has been done with both humans and chimpanzees using a form of DNA called mitochondrial DNA. They determined that the common ancestor of chimps lived 1.4 million years ago, while humans can date their genetic Adam and Eve to just 450,000 years ago.