I suspect this is just my evolutionary tribal instinct kicking in. But for now, I'm happy to restrict my moral sphere of influence to the human race, at least as a first approximation. The 'human race' is the code-word I use for a particularly level of cognitive competence which I consider necessary for full moral consideration. There may be more things in heaven and earth than in our philosophy, but at least we humans have the sentience to appreciate it.
But animal rights activists often produce what they think is a rhetorical trump card in response. "Babies really aren't that much different from adult great apes" they smirk. "You're just a bigoted speciesist! Ha!". The central conceit of course is an empircal assertion. If chimps, gorillas and bonobos are indeed as smart or smarter than infants, then perhaps my moral instincts should yield to the hard data.
I am no expert of course, but the claim that babies and apes are intellectually equivalent has always struck me as a little suspect. While they might seem to be comparable in their mental achievements, the obvious potential of a baby's mind (in that it becomes an adult human mind) is immense. By comparison, apes never develop anything more than rudimentary language or achieve the kind of social intelligence that is de rigeur for humans. Just generally, they seem to lack the ability to respond to cultural scaffolding in the same way that we can.
Jonah Lehrer suggests why. The brain of a baby isn't inactive. Rather it is hyperactive, abuzz with neuronal activity and absorbing information much more broadly than adults do. Young children seem to lack the sort of cognitive sieves that humans typically use to filter out irrelevant information and attend to particular tasks. This is not a hinderence, but rather a cunning adaptation to accelerate the environmental learning that development requires. As we grow up, this open-ended information sink is gradually pruned down to the focussed processing machine that is the adult brain.
To me, results like this highlight our exalted status in the natural order. We shouldn't be bashful - we truly are on a different plateau to the rest of the animal kingdom. Basing the moral uniqueness of the human race on a sophisticated IQ test might feel like shaky ground. But this edifice doesn't crumble as easily as we might think.