Apes, monkeys split earlier than fossils had indicated.

The evolutionary precursors of modern apes and people diverged from ancient monkeys between 29 million and 34.5 million years ago, a new genetic analysis concludes. This evolutionary parting of the ways had previously been placed at between 23 million and 25 million years ago.

Michael E. Steiper of Hunter College of the City University of New York and his colleagues first consulted the latest fossil evidence to estimate that the human evolutionary family separated from chimps' ancestors between 6 million and 7 million years ago, while the macaque monkey lineage diverged from its baboon ancestors between 5 million and 7 million years ago.

The researchers used the timing of these splits to calibrate rates of genetic evolution for apes and monkeys. They then employed a computerized technique to identify and compare similar sequences cover roughly 150,000 basic components of DNA from people, chimps, macaques, and baboons. These data yielded the team's revised age estimate for the ape-monkey split.

Because the oldest-known ape fossils date to no more than 25 million years ago, scientists will need to confirm the new genetic portrait with finds of yet older fossils, the researchers note. Their report appears in the Dec. 7, 2004 Proceedings of the National Academy of Sciences.