Nov 5, 2010 17:47 GMT  ·  By

A new statistical model suggests that the evolutionary break-up between humans and chimpanzees occurred 8 million years ago, 3 million years earlier than what was previously thought.

For decades, paleontologists agreed that humans evolved some 5 or 6 million years ago, and their estimations relied on fossils.

The only problem is that fossil records are not always very complete, and if we take a look at today’s primates, at all of the fossils discovered so far and if we rely on DNA evidence, the computer model’s suggestion that the evolution took a while longer makes sense.

This model considers the gaps in the fossil records and fills them with statistics, just like it’s done in commerce and science.

The technique covers more overall information than what was previously done, with only some individual fossil dates, explains Robert D. Martin, curator of biological anthropology at the Field Museum, and a co-author of the new study.

He says that there is actually an example that sustains this new evolution theory, and he talks about a skull fossil discovered in Chad (central Africa).

The fossil called Sahelanthropus tchadensis and nicknamed Toumaï – ‘hope of life’ in the local Goran language, became even more interesting once the paleontologists realized that it had many human characteristics.

This and the fact that it was about 7 million years old, seemed to suggest that is was a human fossil and that the evolutionary divergence of humans from chimpanzees likely occurred a bit earlier.

Now that the estimates are revised, it should help scientists to better interpret the history of human evolution, Martin said.

After working with mathematicians, anthropologists and molecular biologists, he thought that it might be possible to integrate evolutionary information of genetic material of several other species with the fossil record, and maybe get a more complete picture.

It is true that comparing DNA among related animals can establish how their common genes evolved over time but it cannot say when the genetic divergence happened.

This new approach to dating evolutionary history is actually built upon earlier work by Martin and colleagues, because back in 2002, they had published a paper that said that the last common ancestor of known primates lived 85 million years ago.

This means that 20 million years before the extinction of dinosaurs, there were early versions of primates that also lived and evolved, and this theory is actually challenging the one that says that mammals didn’t really thrive when dinosaurs were still alive.

This new analysis is related in a Systematic Biology paper.