Evolution (Introduction)

by dhw, Tuesday, October 13, 2009, 10:03 (5519 days ago) @ David Turell

David: There is definite evidence, not proven, that humans are the main track and chimps and other apes branched off from us, after the split from the common ancestor...-C.O. Lovejoy: The discovery of Ar. Ramidus also requires rejection of theories that presume a chimpanzee or gorilla-like ancestor to explain habitual upright walking. Ar. Ramidus was fully capable of bipedality and had evolved a substantially modified pelvis and foot with which to walk upright. -I'm certainly not going to argue about this, as I'm out of my depth, but there are things that I simply don't understand. The following are therefore genuine questions, and I'd be most grateful if you or anyone could supply at least some answers.-1) Normally when I read "the common ancestor", I assume it's the ancestor common to humans and apes, but if apes branched off the hominid line, what was the common ancestor common to? And don't apes then become irrelevant to human ancestry?-2) If apes did indeed branch off from humans, is it not possible that Ardi's long arms and opposable toes represent a development from the shorter arms and non-opposable toes of non-tree-climbing hominids? And that the all-important projecting canine (though I thought that was a purely male feature) plus aggressive behaviour came after Ardi? In other words, that she's moving away from the hominid line towards chimpanzeedom?-3) Ardi is estimated to be 4.4 million years old. I thought the conventional theory was that humans and apes split from the "common ancestor" about 6 million years ago, i.e. long before Ardi hit the ground. So if chimps and gorillas already existed, say, a million or so years before her, how does she disprove the theory of the chimpanzee-like ancestor? Wouldn't we need to know for sure that chimps did NOT exist before her?-I apologize for the ignorance underlying these questions, but perhaps I'm not the only one in need of enlightenment.