Should we confer fundamental rights on nonhuman animals? Or would this undermine the rights of human beings? I answer these questions, first, by showing that they are not new, but go back at least as far as the eighteenth century. I identify two partly conflicting intellectual currents of the time—egalitarianism and naturalism—and illustrate, with the writings of French Enlightenment philosophers Jean-Baptiste Salaville and Jean-Claude Delamétherie, how these currents informed their accounts of human and animal rights, respectively. Second, I show the importance of this insight from intellectual history by portraying two antithetical fundamental rights ideal-types which are based on these currents and are still prevalent in today’s rights debates and practices: the Aristocratic conception of fundamental rights which has taken its cue from egalitarianism, and the Meritocratic conception to which naturalism has given rise. I unpack three central features of these conceptions and argue that, because they are located on opposite sides of a spectrum of fundamental rights conceptions, the strengths of one conception are the weaknesses of the other. Lastly, I draw critical practical lessons from this fact by showing that the most viable practical path forward is a middle ground between the Aristocratic and the Meritocratic conception that combines their strengths while minimising their weaknesses. Concretely, I propose the extension of fundamental rights (and cognate concepts such as legal personhood) to some other deserving animals on the basis of species membership rather than individual capacities (I call this the Species Membership Approach, or SMA). Although SMA conflicts with the orthodox anti-speciesism in animal rights scholarship, I demonstrate using three illustrative cases that, in law, there are compelling political and practical reasons for adopting SMA.