His argument is nonsense and relies on two major flaws:
A. He doesn't understand what taxonomy is.
B. He doesn't understand that an organism and the parts of an organism are not the same thing.
Farther, his "thoughts and feelings" standard is problematic. People can lose both without going into a vegetative state. By this standard, someone who is concussed, having a seizure or even drinks too much is temporarily not a human. Needless to say, you cannot temporarily drop out of your species. Additionally, not all people think and feel in the same way. Sociopaths cannot feel altruistic empathy, does this mean they are not humans? People with autism see the world much differently than the rest of us, are they human? Of course, but it isn't clear that they are under his standard.
Perhaps more importantly, homo sapiens are not the only species of humans, they are one of more than a dozen known definitively or implied by the fossil record. It is quite likely that there were a lot more species we don't know about (yet). Where do they fit in here?
RandFan basis his belief on what a human is on what the other humans he sees and interacts with look like. Otherwise his tendency to look at pictures of organisms at different stages of development and conclude they can't be the same thing doesn't make sense. If, say, scientists cloned homo habilis out of extinction and RandFan were introduced to one, especially if not told what they were, he would conclude they are not a human. They would be too short, too hairy, their brows too large, their protruding jaw too extreme, their gait would be wrong and their chimp sized brain could never live up to his "thoughts and feelings" standard. He might accept that they were an ape but he would not accept that they were a human. But, of course, they would be just as much a human as he is.
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