The BBC reports:
Ancient humans started down the path of evolving into two separate species before merging back into a single population, a genetic study suggests.
The genetic split in Africa resulted in distinct populations that lived in isolation for as much as 100,000 years, the scientists say.
That's one possibility, anyway; the reporter adds that "other scenarios could also account for the data." The paper, published in the American Journal of Human Genetics, is available here.
[Via The Art of the Possible.]