Chimps mature with human ancestor.

Wild chimpanzees have taken a bite out of scientific assumptions about the growth rate of one of our most prominent Stone Age relatives.

New measurements of dental-growth rates of wild chimpanzees provide a more accurate benchmark for estimating comparably slow growth in Homo erectus teeth, say Adrienne Zihlman of the University of California, Santa Cruz and her colleagues.

"Our data suggest that wild chimpanzees and Homo erectus didn't differ from each other as much as previously thought," Zihlman says.

The relatively quick tooth growth in captive chimps has typically been contrasted with the slower tooth development in human ancestors. However, dental growth occurs much more slowly in wild chimps than in their captive comrades, the researchers report in the July 20 Proceedings of the National Academy of Sciences.

Zihlman's team examined skeletal samples from 18 wild chimpanzees of known ages, ranging from 1.8 to 16.5 years. For these animals, infancy lasted until about 4 years of age and dental maturity occurred between 12 and 13 years. In captive chimps, infancy ends at around age 3 and maturity is reached at about age 10.

This discovery challenges the view that evolution proceeded gradually from a fast-growing chimplike ancestor around 8 million years ago to a slower-growing H. erectus, which lived from about 1.6 million to 400,000 years ago, and then to an even slower-developing Homo sapiens.--B.B.