January 24, 2006

Study Shows Chimps Closer to Humans Than to Apes

WASHINGTON -- Chimpanzees may be more closely related to human beings than they are to other apes, U.S. researchers reported on Monday.

And a second, separate study showed that humans are busily pushing another close cousin, the orangutan, into extinction.

Both shed light on the complex and often unhappy relationships between humans and our closest relatives, the great apes.

Writing in the Proceedings of the National Academy of Sciences, scientists at the Georgia Institute of Technology said they found genetic evidence that chimpanzees may be more closely related to humans than to gorillas and orangutans.

Soojin Yi and colleagues looked at mutations in the so-called molecular clock, using the mutation rate in DNA.

"Intriguingly, both humans and chimpanzees appear to have evolved slower than gorillas and orangutans," they wrote in their report.

Experts have long known that humans and chimps share much DNA, and are in fact 96 percent identical on the genetic level.

Yi's team looked at several specific genes and compared the difference between human and chimpanzee.

One very noticeable difference is the longer generation time of humans.

"Humans take almost twice as long to reach sexual maturity as chimpanzees (Pan troglodytes) and gorillas (Gorilla gorillas), have a longer lifespan, and have a longer gestation period as compared to any nonhuman hominoid," the researchers wrote.

Their molecular clock suggests humans evolved this trait just a million years ago. Humans and chimpanzees are believed to have diverged from a single common ancestor about 7 million years ago.

"For the first time, we've shown that the difference in the rate of molecular evolution between humans and chimpanzees is very small, but significant, suggesting that the evolution of human-specific life history traits is very recent," Yi said in a statement.

While humans are closely related to the great apes, they are driving many populations of chimpanzees, gorillas and orangutans into extinction.

Writing in the journal Public Library of Science Biology, Benoit Goossens of Cardiff University in Britain and colleagues said their genetic study of orangutans showed a recent catastrophic collapse in genetic diversity.

"This is the first time that a recent and alarming decline of a great ape population -- brought about by man -- has been demonstrated, dated, and quantified using genetic information," Goossens said in a statement.

They collected hair and feces samples and documented 200 individuals living in the forests of Malaysia's Sabah state. The genetic pattern suggested that was many fewer animals than in the past.

"The genetic study shows that there is a high risk of extinction of the orangutan in Sabah in the near future if this decline goes on unabated," said Marc Ancrenaz of the Kinabatangan Orangutan Conservation Project in Sandakan, Malaysia, who also worked on the study.

"The major threat to the long-term survival of orangutans in Sabah is linked with oil palm plantation development and forest destruction. Illegal killing also contributes to this decline."