Astr0, I was merely suggesting that the "female" animal rights manifesto (that all things furry and cute should be preserved, whilst those creatures horrid and ugly, like spiders, should be exterminated) should not be persued: we need to respect all creatures in the web of life, lest we suddenly realise just how inter-connected humans are to their ecosystem.
Steve: I'm just finishing a book called The Symbolic Species, by Terrence Deacon, which is subtitled The co-evolution of language and the human brain. While this is, in fact, a scientific dissertation and doesn't lend itself readily to summary, I can give a few points here. (I did intend to make a more detailed post about it, later, once I had finished.)
Basically, humans are unique in that they use symbolic logic. teaching chimps is difficult (but see below), because they do not grasp some of the counter-intuitive logic required to make specific examples less important than the general rule they represent. For example, teaching a chimp a sentance requires that all the nonsensical sentences are overtly demonstrated as wrong; the chimp rarely (if ever) is able to make this judgement.
I have copied a couple of relevant passages from chapter four, below.