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Chimps May Have Closer Links to Humans

May 20, 2003

By RANDOLPH E. SCHMID, Associated Press Writer

WASHINGTON - It may be time to move over and share the human branch of the family tree with chimpanzees, says a researcher who has studied how closely the two are related.

Humans and chimps share 99.4 percent of DNA — genetic code for life — according to a team led by Morris Goodman of the Wayne State University School of Medicine.

"We humans appear as only slightly remodeled chimpanzee-like apes," said Goodman.

The study, published in Proceedings of the National Academy of Science, proposes that chimps be added to the genus Homo, currently reserved only for humans.

It's an idea sure to spark renewed debate about evolution and humanity's relationship with animals.

The battle over whether humans are related to chimps, gorillas and other primates has raged since 1859, when Charles Darwin described evolution in "Origin of Species."

The dispute between religious and scientific factions got its greatest notoriety in 1925 when Tennessee school teacher John Scopes was convicted of teaching evolution.

It continues to this day. Kansas reinstated the teaching of evolution 18 months after the state school board voted to drop it from classes. Alabama's school board voted to put stickers on biology books warning that evolution is controversial.

Goodman's team did not address evolution directly but proposed that humans and chimps be considered branches of the same genus because of their similarities.

A genus is a group of closely related species. The human species, Homo sapiens, stands alone in the genus Homo. But there have been other species on the branch in the past, such as Homo neanderthalensis, or Neanderthal man.

Chimpanzees are in the genus Pan, along with bonobos, or pygmy chimpanzees.

Goodman's proposal would establish three species under Homo. One would be Homo (Homo) sapiens, or humans; the second would be Homo (Pan) troglodytes, or common chimpanzees, and the third would be Homo (Pan) paniscus, or bonobo chimpanzees.

There is no official board in charge of placing animals in their various genera, and in some cases alternative classifications are available.

"If enough people get agitated by this and think it's something to be dealt with, there may be a symposium that takes this as the central issue and determines if this is a reasonable proposal," Goodman said. "I think it's a reasonable proposal, of course, or I wouldn't have proposed it."

Richard Sherwood, an anthropologist at the University of Wisconsin, isn't so sure.

That chimps and humans are closely related and share a common ancestor about 7 million years ago is well known, Sherwood said, but that doesn't mean they belong in the same genus now.

Goodman's paper cites a proposal by George Gaylord Simpson that chimps and gorillas be combined in one genus; gorillas are in the genus Gorilla. Goodman says chimps are more closely related to humans than to gorillas and thus should be added instead to Homo.

Sherwood says Simpson made his chimp-gorilla proposal in 1963, and no one is arguing today to put both species in the same genus.

"To go hunting for an historical reference like that and then use it as the sole criteria for suggesting a major shift in primate systematics is difficult to take seriously," Sherwood said.

Reclassification of chimpanzees would cause major changes in the way anthropology students learn the relationships among various types of animals.

In their study, Goodman and colleagues compared 97 genes from humans, chimpanzees, gorillas, orangutans, Old World monkeys and mice.

Genes from humans and chimps most closely resembled each other, followed by orangutans and Old World monkeys. None of the other creatures was closely related to mice.

Tracking mutation rates in the genes, the scientists estimate that the common ancestor of chimps and humans diverged from gorillas about 7 million years ago, and then separated into two species between 5 million and 6 million years ago.

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