Edit (9:58pm): Neat! The theory is that Neanderthals died out because they were not as agile as Cro Magnon--couldn't run long distances or jump easily, as demonstrated by their small semi-circular canals, very broad pelvis, and deep, wide ribcage. They couldn't survive a climate change that diminished the forests they were accustomed to and increased areas of grassy plains, where running was a better survival trait.
Also fascinating was a documentary about a chimpanzee named Oliver, who is an extremely unusual chimp, as he is able to walk comfortably upright for extended lengths of time and was unusually humanlike in some of his behaviors. I had never heard of Oliver before, which is surprising, because I love geeky genetics, anthropological, primate stuff like this. There was speculation in the 70's that he might be a chimp/human hybrid, but this has been disproved. He does have an unu7sual gene sequence, though, which appears to be the cause of his unusual traits.