might run by fits and starts, we ran a test to measure how much mitochondrial DNA has evolved in populations founded at a known time.

The aboriginal populations of New Guinea and Australia are estimated to have been founded less than 50,000 to 60,000 years ago. The amount of evolution that has since occurred in each of those places seems about one third of that shown by the whole human species. Accordingly, we can infer that Eve lived three times 50,000 to 60,000 years ago, or roughly 150,000 to 180,000 years ago. All our estimates thus agree that the split happened not far from 200,000 years ago.

Those estimates fit with at least one line of fossil evidence. The remains of anatomically modern people appear first in Africa, then in the Middle East, and later in Europe and east Asia. Anthropologists have speculated that in east Africa the transition from anatomically archaic to modern people took place as recently as 130,000 years ago [see "The Emergence of Modern Humans," by Christopher B. Stringer; Scientific American, December 1990].

On the other hand, a second line of evidence appears to conflict with this view. The fossil record shows clearly that the southern parts of Eurasia were

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