Jonah, I think that the point that Andrew was asserting could be crudely stated as the idea that the kinds of differences that can be described between humans and other animals are the same kinds of differences that can be found between various pairs of non-human animals, and that there is no special kind of difference between humans on one hand and non-human animals on the other that is both categorical and relevant for establishing a unique moral category for humans.
As I said, I think that there is no scientific evidence for such a distinction (and in fact, it is my intuition that there never could be such scientific evidence), but that this is a very different statement than the assertion that science has proven that there is no such distinction.