hundred thousand years, there were three groups of ancient humans, modern humans, neanderthals and homoerectus. it was a simple picture where 400,000-year-old specimens were basically common ancestors of modern humans and neanderthals. what we found in the last five years as we se questioned ancient dna is there were groups we didn't know about. this group in spain is closely related. this little part of the dna to siberian hammon gyms that lived years ago. we have a complicated mix. >> there may have been multiple species of humans living at the same time? >> it's a great problem for people like me. we have a complication that they are different, they were mixing to some degree. when we call them species, we are not talking about species in the sense of they weren't able to interbreed. we find, in fact, that humans are part neanderthal and part this other population we didn't know about. and the neanderthals are part other stuff. it's a crazy mixture of things that - it's like a dr seuss world in the past. >> when you look at people in different parts of the world, they may have more neandert