Study: Put Chimps In Human Family Tree

Chimpanzees are more closely related to people than to gorillas or other monkeys and probably should be included in the human branch of the family tree, a research team says.

The idea, sure to spark renewed debate about evolution and the relationship between humans and animals, comes from a team led by Morris Goodman at Wayne State University School of Medicine in Detroit.

Currently, humans are alone in the genus Homo. But Goodman argues, "We humans appear as only slightly remodeled chimpanzee-like apes." He says humans and chimps share 99.4 percent of their DNA, the molecule that codes for life.

The report is being published in Tuesday's online issue of Proceedings of the National Academy of Sciences.

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

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

And it continues to this day: Kansas reinstated the teaching of evolution this year, 18 months after the state school 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 didn't 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, 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 J. Sherwood, an anthropologist at the University of Wisconsin, isn't so sure.

The fact 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 that, because chimps are more closely related to humans than to gorillas, they be added instead to Homo.

Sherwood says Simpson made that proposal in 1963 and no one is arguing today to put chimps and gorillas 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 between various types of animals, an area already involved in the debate between evolution and creationism.

Walt Brown of the Center for Scientific Creation in Phoenix, Ariz., argues that since the sequencing of human and chimpanzee DNA is not complete, saying people and chimps are that much alike is "baloney."

"We have similarities with chimpanzees, but there are a heck of a lot of differences too," Brown said.

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.