Neanderthals and modern humans not only coexisted for thousands of years long ago, as anthropologists have established, but now their little secret is out: they also cohabited.
At least that is the interpretation being made by paleontologists who have examined the 24,500-year-old skeleton of a young boy discovered recently in a shallow grave in Portugal. Bred in the boy's bones seemed to be a genetic heritage part Neanderthal, part early modern Homo sapiens. He was a hybrid, they concluded, and the first strong physical evidence of interbreeding between the groups in Europe...
http://cogweb.ucla.edu/ep/Neanderthal.html
Methinks it was the interbreeding that wiped out the Neandertal...hybrids are infertile, are they not?
Hybrids are usually infertile, but not always. A lot depends on the distance between the species of the parents.
http://www.messybeast.com/genetics/hybrid-mammals.html From your link:
The age of the skeleton, determined by radiocarbon dating, showed that full Neanderthals had apparently been extinct for at least 4,000 years before the boy was born. "This is no love child," Dr. Trinkaus said, meaning that this was not evidence of a rare mating but a descendant of generations of Neanderthal-Cro-Magnon hybrids.
Instead of seeing a species split into two, we're talking about it splitting into three. Since we seem to have only one sample of a hybrid line, could the child be an example of a child with some kind of growth disorder? Did you see my "Egil's bones" post?