last shared a common ancestor between five and seven million years ago," says Blair Hedges, professor of biology at Penn State. "Although this conclusion does not exclude younger or older dates as being possible, it says they are less likely to be correct." Hedges, who also is an astrobiologist, adds that "knowing the timescale of human evolution, and how we changed through time in relation to our environment, could provide valuable clues for understanding -- in a more general sense -- the evolution of intelligent life."

Walker, a paleoanthropologist and Evan Pugh Professor of Biological Anthropology and Biology at Penn State, has discovered and studied fossil hominids and other primate species that pertain to the question of the human-chimp divergence. "While this research does not pinpoint the precise time of the split, it tells us that proportional differences on branches in family trees should be considered when proposing new times. For example, we now know that a 10-to-12-million-year human-chimp split would infer a divergence of Old World monkeys from our lineage that is too old (50-to-60-million years ago) to reconcile with the current fossil record of primates," says Walker.

What then is the next step? Although some additional improvement is possible by including more genes and more species, "the greatest opportunity now for further narrowing this estimate of 5-to-7-million years will be the discovery of new fossils and the improvement in geologic dating of existing fossils," says Walker.

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Contact: Barbara K. Kennedy
science@psu.edu
814-863-4682
Penn State
19-Dec-2005

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