The Neanderthal-Human Split: (Very) Ancient History

March 17, 2008 -- Neanderthals and humans once shared a common ancestor, but we split from the stocky, hairy hominid group as long as 400,000 to 350,000 years ago, concludes a new study.

That estimate matches prior DNA studies, putting a date to the time when human beings first emerged on the planet. But would these first humans have been anatomically just like us? Probably not, suggests lead author Timothy Weaver, an anthropologist at the University of California at Davis.

"Early fossils along this lineage are quite different from later ones," he told Discovery News.

Fast evolution, in fact, probably drove the initial Neanderthal/human divergence, which likely began as genetic drift -- random changes in DNA. As the two groups parted ways, their changing environments likely drove more substantial changes in body shape and size, in response to differing needs.

Weaver and colleagues Charles Roseman and Chris Stringer created a model to determine how long it would have taken genetic drift to create the cranial differences observed between Neanderthal and modern human skeletons.

The model used prior information on how microsatellites, aka "junk DNA," can change, or drift, over time in a species. Over time, those changes can accumulate enough for an entirely new species to evolve.

The researchers applied the model to 37 cranial measurements collected on 2,524 modern and 20 Neanderthal specimens. Their findings are published in this week's Proceedings of the National Academy of Sciences.