NO SEX, PLEASE

By Philip Elmer-DeWitt

Anthropologists have long known that modern man and the brawny, heavier-browed creatures known as Neanderthals coexisted on the planet for tens of thousands of years. What they don't know is how the two species got along. Did they interbreed, as some scientists contend, producing among their descendants the people who now populate Europe? Or did they compete for food and shelter, with Neanderthals eventually losing the struggle and disappearing for good 30,000 years ago?

A landmark report in last week's issue of the journal Cell suggests that whatever else Homo sapiens and Neanderthals did, they probably did not make love. In a tour de force experiment that involved extracting a microscopic strand of ancient DNA from the arm bone of a Neanderthal skeleton, a team led by Dr. Svante Paabo of the University of Munich showed that the two species have almost nothing in common, genetically speaking.

All living creatures share a certain genetic heritage. But comparing a 378-unit sequence of DNA taken from mitochondria within a Neanderthal cell to modern DNA, Paabo's team found striking differences. Contemporary humans differ from one another by an average of eight variations in that sequence. The Neanderthal specimen differed in 27 places. By comparison, there are only 55 differences between modern humans and chimpanzees.

This suggests that Neanderthals split off from the human family tree quite a bit earlier than most scientists believed. The ancestral population of all modern humans is thought to have emerged about 150,000 years ago. Humans and chimps diverged at least 4 million years earlier. Based on the new DNA study, our ancestors and Neanderthals split up about 550,000 to 690,000 years ago--and were never reconciled.

--By Philip Elmer-DeWitt