Mandel Ngan / AFP - Getty Images Click for interactive: Skulls
of early Homo sapiens (right) and a Neanderthal (left, in
background) sit at the Smithsonian's National Museum of Natural
History. Scientists say a third hominin group may have co-
existed with those two groups 40,000 years ago. Click on the
image to learn more about human evolution, in the past and
perhaps in the future. A DNA sample taken from an ancient pinky
bone suggests that a previously unknown group of human ancestors
mixed it up with Neanderthals and modern humans 40,000 years
ago. Was it a completely different species? Too early to say,
but it might depend on what your definition of "species" is. The
finding, published in this week's issue of the journal Nature,
emerged from a check of DNA samples from Denisova Cave in
southern Siberia's Altai Mountains. Anthropologists know that
the cave was occupied by human ancestors off and on for at least
125,000 years, based on the artifacts and bits of bone found
there. The pinky bone was found in