This skull, ffound in Pestera cu Oase - the Cave with Bones - in southwestern Romania, includes features of both modern humans and Neanderthals, possibly suggesting that the two hominid species may have interbred thousands of years ago. The skull is discussed in a paper by Erik Trinkaus of Washington University in St. Louis. The report appears in Tuesday's issue of Proceedings of the National Academy of Sciences. (AP Photo/National Academy of Sciences)