In contrast to people like John Finnis, I believe that the Aristotelian and Thomistic tradition of ethical naturalism is rooted in a biological understanding of human nature. A few years ago, Alasdair MacIntyre took a similar position despite his earlier disagreement. In his remarkably influential book After Virtue (1981), MacIntyre tried to defend an Aristotelian and Thomistic view of ethics as founded on the moral and intellectual virtues. But he insisted that his ethical view did not depend on Aristotle's "metaphysical biology." Almost twenty years later, in Dependent Rational Animals (1999), he conceded that "I was in error in supposing an ethics independent of biology to be possible." He generously referred to my Darwinian Natural Right as an influence on his change of mind. He had decided that we cannot explain how we develop into moral beings unless we explain how our biological nature as animals makes such a form of life possible for us. He also observed that denying or denigrating our bodily nature as animals obscures our natural vulnerability and dependence. MacIntyre went on to argue that the Aristotelian and Thomistic understanding of the animal nature of human thought and action is confirmed by Darwinian biology.
That Darwinian biology supports Thomas Aquinas's natural law is an idea that I have developed in various writings, most fully in "Thomistic Natural Law as Darwinian Natural Right," an article published in the winter 2001 issue of Social Philosophy & Policy. (This whole issue of the journal was also published as a book by Cambridge University Press--Natural Law and Modern Moral Philosophy.)
But for some strange reason my absolutely conclusive arguments have not persuaded all of the scholars of Thomistic natural law. In particular, Craig Boyd has challenged my position. His reasoning is laid out in an article--"Was Thomas Aquinas a Sociobiologist? Thomistic Natural Law, Rational Goods, and Sociobiology," in Zygon (September 2004)--in a book chapter in Evolution and Ethics (edited by Philip Clayton and Jeffrey Schloss, 2004), and in Boyd's recent book A Shared Morality: A Narrative Defense of Natural Law Ethics (2007).
Boyd contends that "although much of natural law morality is clearly rooted in human biology, Arnhart's claim that the entirety of human morality is merely biological certainly cannot be supported by natural law morality." The natural morality of the natural inclinations to self-preservation, conjugal bonding, parental care, and social life is rooted in animal nature. But "the human ability to deliberate, judge, and guide activities transcends animal nature." As uniquely rational animals, human beings have "rational goods" that transcend human biology.
For Boyd's position, the crucial passage in Aquinas's Summa Theologica is the famous passage on the three levels of natural law:
"Since good has the idea of an end, and evil the idea of a contrary, all those things to which a human being has a natural inclination reason naturally apprehends as good, and consequently as objects to be pursued, and the contraries of these as evil and to be avoided. Therefore, the order of the precepts of the natural law is according to the order of the natural inclinations. For there is first in a human being an inclination to good according to the nature which he shares with all substances: insofar as every substance seeks the preservation of itself accroding to its own nature. And according to this inclination, those things through which human life is preserved and threats to life avoided belong to the natural law. Secondly, there is in a human being an inclination to some things more special to him according to the nature that he shares with other animals. And accroding to this inclination, it is said that those things are of natural law 'that nature has taught all animals,' such as the joining of male and female, the education of children, and similar things. In a third mode, there is in human being an inclination to good according to the nature of reason, which is proper to him: thus a human being has a natural inclination to know the truth about God, and to live in society. And according to this inclination, those things that pertain to this kind of inclination belong to natural law: for example, that a human being avoid ignorance, and that he not offend those others with whom he must live, and other such things that pertain to his inclination" (I-II, q. 94, a. 2).
Boyd agrees with me that the first two levels of natural human inclinations are shared with other animals, and therefore they are rooted in biological nature, and they are open to study by Darwinian science. But he disagrees with me by arguing that the third level of natural inclinations--based on the uniquely human capacity for reason--transcends human biology.
In reply to Boyd, I say that his reading of Aquinas confuses "natural law" with "divine law." Natural law, Aquinas believes, guides human beings in pursuit of their natural ends--earthly happiness. But insofar as human beings are directed to supernatural ends--heavenly beatitude--they need the divine law of Biblical revelation. This supernatural or divine law transcends the capacity of human nature. But natural law is fully within human nature (I-II, q. 91, a. 4).
In distinguishing the various levels of natural law, Aquinas identifies the "generic nature" that human beings share with other animals, the "specific nature" that they share with other members of the human species, and the "temperamental nature" unique to particular human individuals (I-II, q. 46, a. 5; q. 51, a. 1; q. 63, a. 1). Aquinas draws this three-leveled analysis from Aristotle's biology. Darwinian biology employs the same analysis in that some human traits are shared with other animals, some are unique to human beings, and some are unique to particular individuals.
Boyd stresses the human uniqueness of "the human ability to deliberate, judge, and guide activities." But, of course, Darwin recognizes this as well: human beings have a natural ability to deliberate about their desires in the light of past experience and future expectations that makes human beings unique in their morality. This uniqueness does not "transcend animal nature," because it is part of the uniquely human animal nature. Human beings have mental capacities that emerge from the evolution of the brain that give them a unique freedom to deliberate about their conduct and to freely choose between alternative courses of action. I take this up in various parts of Darwinian Natural Right and in the chapter on "Emergence" in Darwinian Conservatism.
But what should one say about Aquinas's reference to the "natural inclination to know the truth about God"? Does this show a transcendence of human biological nature? I would say that Aquinas understands the "natural desire to know God" as fully within human nature and natural law in a manner that can be accounted for by Darwinian naturalism.
A serious study of Aquinas on this point would require some study of passages scattered throughout the Summa Theologica (I, q. 12, a. 1; I-II, q. 3, a. 8; q. 99, a. 3; II-II, q. 81, a. 5; q. 85, a. 1) and Summa Gentiles (I, 11; III, 25, 50-51, 57, 119).
As I read it, this "natural inclination to know the truth about God" corresponds to what I have identified as the natural desire for religious understanding. The natural rationality of human beings inclines them to seek the causes of everything, even to the point of asking for the first cause or ultimate explanation of everything. Why is there something rather than nothing? Why is nature ordered as it is and not differently? If we do not accept the order of nature as a brute fact--That's just the way it is!--we might ask for the uncaused cause of all natural causes, and that would lead us to God as First Cause. This is Aquinas's natural theology. From natural effects, we can reason our way to God as the First Cause. But this purely natural inference of human reason cannot take us to the essence of God. For that, we need revelation.
Darwin acknowledged that when we ask about the first cause of life or of the universe as a whole, we reach the limits of human reason, and this leaves an opening for God as Creator or uncaused cause. This yearning to explain everything is a uniquely human desire, but it is still part of human biological nature insofar as it expresses a natural desire for understanding that arises from the emergent powers of the human brain.
I have written a paper elaborating my responses to the various criticisms of my argument for Thomistic natural law as Darwinian natural right.
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