Arnhart is certainly right that, for St. Thomas Aquinas, natural law has a biological foundation. He’s also right that the Finnis attempt to defend Thomistic natural law without nature is implausible. I do think MacIntyre unrealistically narrows the gap between us and the dolphins as "dependent rational animals." There’s a huge difference between our eros or love and dolphin and chimp eros (which is only loosely called eros). We’re both much more independent and much more deeply dependent than our fellow creatures. Let me add that the distinctively Thomistic position is particularly difficult to defend these days. Here’s one reason why: For both Locke and Darwin, reason or words are just tools. For Locke, they’re for the preservation of the free individual, and for Darwin the preservation of the species. For St. Thomas, they’re for a lot more than that.