Social Darwinism has been discredited. I'm talking about sociobiology, which is currently part of the scientific world view. I'm saying that any theory that purports to explain why humans developed the concept of rights must be consistent with this world view. I submit that only contractarian theories meet the test of consistency with the scientific world view.
Natural law is teleological.
Communitarianism, utilitarianism, and Nietzsche's moral philosophy are anti-Darwinian. I can't think of any theory other than contractarianism that offers a plausible explanation of the development of rights in human society. From the available empirical evidence, it appears that only humans are capable of this type of reasoning, even though some non-human animals display rudimentary forms of morality. Unless you can find some flaw in the argument outlined above, I don't see how you can hold that the concept of rights can be coherently applied to non-humans. The argument is not question-begging unless you can show some premise of mine that is not supportable.