You have to be careful, though, because the train of thought that makes rights contingent on actual ability to perform leads inexorably to a justification of eugenics. Once you agree that even humans may not really have rights unless they meet a certain bar, you create all sorts of incentives to start screwing with the bar. And we shy away from eugenics not because of the idea itself, but because of what fruit it bore, and there's little reason to believe it would go any better a second time.

Plus you're a distressingly short trip from the bar being "having right and proper political beliefs".

"Speciesism" at least has the virtue of being fairly unambiguous. It may still be the better policy even if it isn't perfect.

I don't think that's what they mean. My interpretation of that statement would be that rights are conferred to species as a whole, not individuals, and it matters whether the species as a whole can bear legal responsibility. Just as you can't take rights away from individual members of a species that can do that, you can't give rights to individuals of a species that can't. How you define what species can and what can't is of course the clincher in that case.

In a way, it's a pretty decent way to look at it. It means all that is required for an entire species to be given personal rights is to prove that they can fulfill the obligations that come with them. It decouples the rights from the good or bad inviduals, and reduces it to "what is this genetic grouping capable of".