Evolution (Introduction)

by dhw, Wednesday, October 14, 2009, 11:09 (5315 days ago) @ David Turell

David: It is very important to understand that the prevailing opinion up until this juncture with Ardi is that we humans descended from an ape-like ancestor. Now that appears not to be the case.-I'm going to be stubborn, not because I know anything, but because I still find it hard to follow the reasoning. -1) Scientists tell us that humans and chimps split from a common ancestor about 6 million years ago (but it could have been a lot more). If the theory is correct, it should be possible to find hominid fossils dating back 6 million years or so. We've now found one that dates back only 4.4 million years, so why is human ancestry suddenly turned on its head?-2) The theory has been that the "common ancestor" was "more ape-like" than hominid. Presumably this is because we regard humans as more advanced than apes (chimps might disagree), and we assume that evolution has moved towards "advancement" rather than in the reverse direction. There is no fossil evidence to prove this assumption or its converse (a "more hominid-like" ancestor), as we have a gap of, say, a couple of million years before Ardi. Aren't both theories therefore pure speculation, although the first seems more firmly based on common sense? However, even if the new theory is correct, why does it make humans "different in kind"? "More hominid-like" is not human, and in any case the "common ancestor" also had ancestors, so didn't we originally still descend from something that was not human?-3) If we really are "different in kind", isn't that because of our brain? But Lucy, we are told, proved that early humans walked upright before they evolved large brains, and Ardi's brain is the size of a chimp's. Is upright walking therefore the criterion for "different in kind"?-Apologies again if I'm missing something obvious.