For years now, ever since genome analysis discovered such things as the fascinating fact every human can trace his or her ancestry (at least in small part) to a single "Eve" back in Africa some 190,000 years ago, it has been common knowledge among anthropologists that humans (Cro Magnons) and Neandertals could not interbreed. For instance, a book I am reading called "The Real Eve: Modern Man's Journey Out of Africa" (copywrited 2004 - my paperback was reissued in 2007) states confidently that "there is no evidence among the tens of thousands of non-Africans who have had their (male and female specific) chromosomes studied for even a minimal degree of this kind of mixing."
It turns out this common knowledge ain't. Up to 4 percent of the DNA of people today (who live outside Africa) came from Neandertals. (Ah, the power of sex!)
The news - shocking to investigators - came from new studies of the Neandertal genome based on 38,000-year-old Neandertal bones from a cave in Croatia. The work was reported in the May 7 "Science." Back in 1997 the lead scientist of the new study, Svante Paabo of the Max Planck Institute for Evolutionary Anthropology in Germany, wrote that his studies at the time showed Neandertals had made no such contribution.
So it goes.
Many people like to research their family trees looking for famous or accomplished forbearers. Few find them. But all can be sure that, going back far enough, they will find folks with huge jaws, flattened craniums, and pronounced brow ridges. (On the bright side, remember that Neandertals, on average, had bigger brains than humans do.)