The results challenge the assumption that human evolution followed a path from a chimplike ancestor to a transitionary Homo erectus and then Homo sapiens, suggesting instead that chimpanzees have more in common developmentally with Homo erectus and that modern humans are the "out-group."

The study was coauthored by Adrienne Zihlman, professor of anthropology at the University of California, Santa Cruz; Debra Bolter, who just earned her doctorate in anthropology at UCSC; and Christophe Boesch, director of primatology at the Max Planck Institute for Evolutionary Anthropology in Leipzig, Germany.

The researchers examined skeletal samples from 18 wild chimpanzees of known ages and compared the data to the dentition of captive chimpanzees, which have been used as a baseline for discussion of hominid origins and the transition from ape ancestors to hominids. The eruption of teeth mark other life events, such as completion of brain growth (90 to 95 percent of brain growth is complete when the first permanent molar erupts) and life-history stages like infancy, juvenile, and adulthood.

The team's analysis consistently showed a slower rate of development of all the teeth of wild chimpanzees compared to captive chimpanzees: Among wild chimpanzees, infancy lasted until about four years of age and mature dentition was reached between 12 and 13 years of age, compared to captive animals whose infancy ended around three years of age and who reached mature dentition about 10 years of age.

"These findings challenge a number of assumptions about the growth of hominids," said Zihlman. "Anthropologists and paleoa
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Contact: Jennifer McNulty
jmcnulty@ucsc.edu
831-459-4399
University of California - Santa Cruz
13-Jul-2004