I find Peter Singer's argument that animals' (specifically mammals') capacity to
I'm having trouble seeing what evolution has to do with it. Many animals, Singer supposes, feel pain. Pain (roughly; the refinements won't matter here) is intrinsically bad, no matter what sort of creature experiences it. Whether animals (or humans) feel pain because of evolution, because a God made them that way, or because we're all sentient animaldroids, designed by mad scientists from Mars is beside the point. Singer's thought is that pain is bad for us, and animals are no different from us in that respect. He isn't making a point about the phylogenetic tree. Cabbages don't feel pain; cats do. So when we're calculating the balance of pleasure to pain, the cat's pain (or pleasure) should be included in the calculation. But since cabbages aren't sentient (so far as we know), there's nothing about the cabbage to add or subtract.