Evolution and Human Behavior has published (online, but not yet in print) an article by Carlton Patrick--"Evolution Is the Source, and the Undoing, of Natural Law." Patrick is a lawyer and a Professor of Legal Studies at the University of Central Florida.
Previously, I have written about the book that Patrick coauthored with Debra Lieberman--Objection: Disgust, Morality, and the Law (2018). I said that the main argument of Lieberman and Patrick in that book is a syllogism: since evolutionary psychology shows that moral emotions like disgust are irrational in ways that are dangerous to society, and since the law should be based on rational principles rather than irrational emotions, disgust (and other moral emotions) should be excluded from the law. I said that that syllogism is false, because the premise that moral emotions like disgust are utterly irrational is false. I argued that research in evolutionary moral psychology shows that moral judgment always combines reason and emotion in a complex interaction. Consequently, moral judgment cannot be properly explained by either a purely emotivist theory or a purely rationalist theory. In explaining moral judgment in this way as the conjunction of reason and emotion, evolutionary moral psychology confirms the tradition of naturalist moral philosophy that stretches from Aristotle and Thomas Aquinas to David Hume and Adam Smith and then to Charles Darwin and Edward Westermarck.
Playing off the title of Patrick's new article, I would argue that evolution is the source of natural law as interpreted by Thomas Aquinas and John Locke and the undoing of natural law as interpreted by John Finnis and Robert George. Patrick's mistake is in assuming that Finnis's (and George's) Kantian distortion of natural law as based on some metaphysical or cosmic order of reason beyond human nature is the correct interpretation of traditional natural law. He thus ignores the fact that the natural law as understood by people like Aquinas and Locke is rooted in human biological nature in a way that can be confirmed by evolutionary moral psychology.
Patrick begins his article by identifying the proponents of the idea of natural law as including Aristotle, Aquinas, Grotius, Locke, Dworkin, Finnis, and George. He then singles out Finnis as "the father of the modern natural law argument," who insists that natural law must be founded on "moral objectivity, be it established by God, the universe, or some metaphysical source." In this way, natural law is based on some "supernatural or metaphysical explanations" that transcend human nature. For Finnis, this metaphysical order dictates certain "basic goods"--life, health, knowledge, play, friendship, religion, and aesthetic experience--that are "fundamental, underived, irreducible."
Patrick can then argue that evolutionary psychology refutes this metaphysical conception of natural law. He explains:
". . . when we talk about morality, we are not talking about a cosmic mandate but rather a set of species-wide psychological instincts that are a part of human nature. These instincts evolved because, over evolutionary time, they helped our ancestors to navigate the highly social world of the evolutionary milieu. Although there are differing views, most evolutionary scholars agree that the general functions of morality are to avoid, navigate, and resolve conflicts of interest in social interactions" (3).
So, if Finnis's metaphysical interpretation of natural law as founded on a "cosmic mandate" is correct, then evolutionary psychology refutes natural law. There are two problems here, however. Patrick simply assumes without proof that Finnis's metaphysical interpretation is correct. And he fails to consider the possibility that there are better interpretations of natural law as founded on human biological nature that could be supported by evolutionary psychology.
There have been many critics of Finnis's interpretation of natural law--including Henry Veatch, Ralph McInerny, Russell Hittinger, and Anthony Lisska. Patrick does not mention, must less answer, these critics. In a series of posts, I have indicated why I agree with the critics. The primary criticism of Finnis is that his version of natural law is natural law without nature, because he rejects the traditional understanding of natural law as rooted in human nature--in the natural desires or natural inclinations of human beings. Finnis actually admits this when he dismisses "the rather unhappy term 'natural law.'" He doesn't like the term "natural law" because it implies that it is rooted in human nature, and that is what he denies (Natural Law and Natural Rights , 35, 198, 280, 374).
Moreover, Patrick does not see that the traditional understanding of natural law is rooted in the principle (as stated by Aristotle, Aquinas, and Locke) that "the good is the desirable," which supports natural law as founded on those natural desires distinctive to human biological nature. This corresponds to what Patrick calls those "species-wide psychological instincts that are part of human nature," which are studied by evolutionary psychologists. I have defended this position in Darwinian Natural Right: The Biological Ethics of Human Nature (1998).
Patrick also does not see that natural rights in Locke's state of nature correspond to the natural instincts in what evolutionary psychologists call the "environment of evolutionary adaptedness" (EEA). I have written about this in various posts (here, here, and here).
This leads me to conclude that while evolutionary psychology denies Finnis's metaphysical natural law, it confirms Locke's human natural law.