Scientists have long tried to tease out the secrets of what makes us human by comparing human behavior to how other species behave, such as chimpanzees.

But now a research team hopes to get at the question another way - by studying the DNA of Neanderthals, early hominids that were similar to humans, said Richard "Ed" Green, a computational biologist at the University of California at Santa Cruz.

"What is clear is that our closest extinct relative is the Neanderthal," Green told an overflow crowd of University of Georgia professors and students in a Coverdell Hall lecture room Tuesday. "They are way more similar to humans than anything else."

Green is part of the research team, led by Svante Paabo of Germany's Max Planck Institute for Evolutionary Anthropology, that partially sequenced the genome of Neanderthals using DNA from bones buried in a Croatian cave nearly 40,000 years ago.

The team already found one big surprise when they compared the Neanderthal DNA to modern humans.

"We know they were reproductively compatible because you are 1 to 4 percent Neanderthal (genetically)," Green said.

In other words, modern humans and Neanderthals interbred, said Green, a Conyers native who got his undergraduate degree at UGA.

Neanderthals arose about 200,000 years ago but went extinct about 30,000 years ago - and no one really knows why. Modern humans date to 130,000 years ago - so humans and Neanderthals coexisted for tens of thousands of years.

But the differences in Neanderthal and human genomes may tell scientists more than the similarities as they try to understand how humans got to be the way we are, Green said.

Some of the genetic differences in humans and Neanderthals seem to be in regions of the human genome involved in autism - a little-understood condition that affects people's ability to interact with other people.

Green and other scientists speculate that modern humans may have genetic mutations absent in Neanderthals that somehow gave us the ability to build bigger social groups than our extinct relatives, Green said.