Human evolution 'took place three million years earlier'

Researchers have found that the evolutionary divergence of humans from chimpanzees took place eight million years ago rather than the five-million-year estimate widely accepted by scientists, the 'Systematic Biology' journal said.

"The revised estimate of when the human species parted ways from its closest primate relatives should enable scientists to better interpret history of human evolution," said Robert Martin, who led the team at the Field Museum.

Working with mathematicians, anthropologists and molecular biologists, Martin has long sought to integrate evolutionary information derived from genetic material in various species with fossil record to get a complete picture.

Comparing DNA among related animals can provide a clear picture of how their shared genes evolved over time, giving rise to new and separate species, Martin said. But such molecular information doesn't yield a timetable showing when the genetic divergence occurred.

Fossil evidence is the only direct source of information about long-extinct species and their evolution, Martin and his colleagues said, but large gaps in the fossil record can make such information difficult to interpret. For a generation, paleontologists have estimated human origins at 5 million to 6 million years ago.

But that estimate rests on a thin fossil record. By looking at all of today's primate species, all of the known fossil primates and using DNA evidence, computer models suggest a longer evolutionary timetable.
The new analysis takes into account gaps in the fossil record and fills in those gaps statistically.

"Such modelling techniques, which are widely used in science and commerce, take into account more overall information than earlier processes used to estimate evolutionary history using just a few individual fossil dates," Martin said.

Under the new estimate, Toumaï would fall within the period after the human lineage split from chimpanzees, Martin said, adding the new approach to dating evolutionary history builds on their earlier work which argues the last common ancestor of today's primates lived some 85 million years ago.

This implies that for 20 million years before dinosaurs became extinct, early versions of primates also lived and evolved. It challenged the accepted theory that primates and other mammals didn't really thrive on the planet until dinosaurs were gone.