There's a confused discussion going on at Crooked Timber about whether there is a "radical difference... between human beings and all other terrestrial species". It's patently obvious that the answer is "yes", so I'm surprised that the majority of CT commenters can seriously deny this. Obviously the human mind is leagues beyond all others in important respects, as evidenced by the fact that no non-humans have yet joined in the debate. Sure, dolphins or chimps might have some capacity to exhibit crude precursors of language and culture, but they pale in comparison to human capabilities. To deny our vast rational superiority would be as ridiculous as denying the vast aquatic superiority of dolphins on the basis that "humans can learn to swim a bit too".
Several commenters seemed to buy the old fundamentalist's canard that only an immaterial soul could explain human exceptionalism. To avoid metaphysical extravagance, then, they seem forced into the absurd claim that humans "really" aren't that different from other animals. But this is silly -- the real problem lies with the first premise. The fundamentalists are mistaken: naturalism is entirely consistent with human exceptionalism.
Fundies object to physicalism because it implies that humans and rocks are made of the same "stuff" (i.e. matter), and thus "must" be the same in kind. The anti-exceptionalist argument, that humans must be like chimps for sharing so much DNA, is similarly foolish. The great fallacy in both is to overlook the importance of arrangement or internal relations between the constitutive 'stuff'. A great poem is obviously of far greater value than a page of random words, even though both are made of the same "stuff" (namely, words). The arrangement matters. Similarly, a chair is vastly different in kind from a newspaper, even if both are made from tree products. And a human being is vastly different in kind and value from rocks, even if both have purely physical constituents. For full knowledge of an object, it does not suffice to learn merely what materials it is composed of, in ignorance of their compositional arrangement. Contrary to the "fallacy of composition", the whole may have properties that differ (and cannot be inferred) from those of its isolated individual parts. This point is so patently obvious that I have to wonder if the fundies who make the "how can 'mere matter' matter?" objection have some kind of mental defect. It's as silly as asking how "dry", "colourless" atoms could suffice to make green grass or wet water.
So when Richard Cownie suggests that the purported human difference is "obviously nothing physical," I respond that he is obviously mistaken. There are hugely important physical differences between the human brain and the brains of other animals. Otherwise we wouldn't be capable of having this debate. Though, if it makes the anti-exceptionalists feel any better, I'd be happy to grant that human infants are similarly miles away, in terms of cognitive development, from the rest of us. (From what I've heard, chimps perform comparably to 3 year old children against several cognitive measures, so it might not be a bad analogy to bear in mind.) You won't find infants, any more than dolphins, starting philosophical academies or building spaceships. There is a vast and undeniable difference here.
Of course, it isn't an entirely unbridgable gulf. Infants do develop into (variously) rational adults, after all. And the human species did evolve from a common ancestor shared with other animals. So one can point to important similarities, I certainly wouldn't deny that. But none of that changes the fact that an adult human being is a very different kind of creature from an adult chimp or dolphin, which in turn are vastly different from ants and earthworms. There is something quite exceptional about the human capacity for general intelligence, or rational thought, which is not found in any other animal. Animals can be cognitively skilled in various domain-specific ways, but they don't have anything remotely comparable to the incredible cognitive plasticity of most humans. We don't need to posit anything so extravagant as an immortal soul in order to be able to accomodate this undeniable fact. Instead, we may simply recognize that the human brain is a remarkable piece of matter.