On Natural Law (On the Law in General) (Excerpt‪)‬

Just as the term nature is understood in different ways, so, too, natural law is defined differently by different people. Civil lawyers see nature as the community of all animals not just human beings. Thus, they understand natural law, as they have defined it in Justinian's Digest and Institutions, in this way: "Natural law is what nature teaches to all animals." (16) In particular, they mean mating, reproduction, and rearing young, since we can see that all animals are naturally bound by this law; that is, that they make babies.