I argue that a Darwinian view of human nature supports the natural law reasoning of Thomas Aquinas. I use the term "natural law" to refer to the following cluster of ideas: (1) animals have innate propensities, (2) the normal development of each kind of animal requires the fulfillment of these propensities, (3) animals with conscious awareness desire the satisfaction of these propensities, and (4) human beings use their unique capacity for rational deliberation to formulate ethical standards as plans of life for the harmonious satisfaction of their natural desires over a complete life. Darwinian biology supports this natural law understanding of ethics by showing how such inborn desires and cognitive capacities arise in human biological nature.
This argument for Darwinian natural law comes up in Darwinian Natural Right, in Darwinian Conservatism, and in the Aquinas chapter of Political Questions: Political Philosophy from Plato to Rawls. But the fullest statement of this argument is in my paper on "Thomistic Natural Law as Darwinian Natural Right," which was published as an article in Social Philosophy & Policy (vol. 18, no. 1, winter 2001) and as a book chapter in Natural Law and Modern Moral Philosophy, edited by E. F. Paul, F. D. Miller, and J. Paul (Cambridge University Press, 2001).
Religious conservatives have objected to my argument by insisting that Thomistic natural law must be founded in the biblical religious belief in God as the Creator of nature who orders nature to his cosmic ends. After all, how can there be a "natural law" without a divine lawmaker? If so, then Darwinian natural science cannot support the Thomistic natural law tradition unless there is some biblical religious belief behind it.
This thinking is well developed in Matthew Levering's new book Biblical Natural Law: A Theocratic and Teleological Approach (Oxford University Press, 2008). But although Levering--a theology professor at Ave Maria University, Naples, Florida--would probably reject my idea of Darwinian natural law, there are some fundamental points of agreement between us.
Levering states his main idea in one sentence: "While all human beings know the natural law at least to some degree, explanations of the character and content of the natural law are greatly assisted by faith, and thus also by biblical revelation" (4). The ambiguity in his position is suggested by the phrases "at least to some degree" and "greatly assisted." He indicates that he is employing a distinction between natural law and explanations of natural law stated by Ralph McInerny: "It would be odd for anyone to say that everyone's grasp of fundamental guides for moral action involves explicit recognition of the existence of God. But it is not odd to say that any adequate account or theory of such fundamental guides must make appeal to God's existence."
I argue that while religious belief can reinforce our natural moral sense, natural morality can stand on its own natural ground in the natural desires of human beings even without any religious belief. A Darwinian science of morality can recognize the importance of religious traditions in sustaining morality. But in so far as morality is rooted in evolved human nature, the natural moral sense can be based on natural human experience without any appeal to supernatural revelation.
As a Christian, Thomas Aquinas believes that the natural moral law is ultimately explained as part of the eternal law of God as the Creator of nature. But still, Aquinas distinguishes the natural law as apprehended in natural human experience and the divine law as revealed to the faithful in the Bible. I interpret this to mean that even those people who do not believe in the Bible as divine revelation of God's moral law can understand and obey natural law. Although Levering generally seems to agree with this, some of what he says in his book suggests that natural law cannot stand on its own without the divine law of the Bible.
At one point, Levering makes a vague reference to my Darwinian Natural Right. He says that my book "equates Darwinian teleology (survival of the fittest) with the teleology of natural inclinations" (12). Although he does not explain his position here, he implies by the context that my "Darwinian teleology" cannot properly explain natural law as based on a divinely ordained cosmic teleology.
This is unclear, however, because elsewhere in his book, Levering seems to endorse the arguments of Alasdair MacIntyre and Jean Porter for a teleology rooted in natural science (170-71). In fact, MacIntyre--in his Dependent Rational Animals--has agreed with my claim that an Aristotelian and Thomistic ethical naturalism can be supported with a Darwinian account of human nature and natural teleology.
In explaining natural law, Aquinas quotes from Ulpian, an ancient Roman jurist: "Natural right is that which nature has taught all animals." To illustrate the natural inclinations that human beings share with other animals, Ulpian referred to the sexual union of male and female and the parental care of offspring as animal propensities that sustain human marriage and family life in conformity to natural law. Like Ulpian, Aquinas speaks of the human disposition to marriage as a "natural instinct of the human species." This biological basis for natural law is also evident in Aquinas's many references to Aristotle's biology and to the zoology of Albert the Great, Aquinas's teacher at the University of Paris.
It is odd that Levering says almost nothing about Aquinas's biological explanations for natural law. He makes some passing references to Aquinas's citation of Ulpian, but without any elaboration. And when he lays out Aquinas's famous description of the levels of natural human inclinations supporting natural law, Levering omits Aquinas's reference to Ulpian (141, 145, 160, 185).
Levering agrees with me about the primacy of Aquinas's claim that "the good is the desirable" (58, 172). He also agrees with me that this Thomistic appeal to natural desires is ignored by John Finnis and his followers who take a Kantian direction in trying to root natural law in "the order of reason" as opposed to the "order of nature" (143-45).
So how important is biblical religion for natural law? At times, Levering seems to be suggesting that we need biblical revelation to resolve moral disputes where natural law by itself is insufficient. But he does not give any clear examples of this.
As I have written previously on this blog, biblical moral teaching often suffers from disputes over its authority, its clarity, and its reliability. Those who are not biblical believers will not accept the authority of the Bible as revelation. Even those in the biblical tradition will disagree about this, because Jews will not always agree with Christians, and Muslims will not always agree with Jews and Christians. Levering assumes the position of a Christian, which suggests that the New Testament has superseded the Hebrew Bible and that the Koran has no authority as revelation.
Moreover, the Bible is often not clear or reliable in its moral teaching. For example, in the debate over the morality of slavery, the Bible could be quoted on both sides. Actually, in every passage of the Bible where slavery is specifically mentioned, it is endorsed. That's why the proslavery people in the American South thought they were the true Christians. The failure of the Bible to properly resolve the debate over slavery is why the American Civil War became a theological crisis for biblical believers.
The teaching of universal love in Jesus' Sermon on the Mount demands pacifism. But a crucial part of natural law is the tradition of just war, which allows for justified killing. Levering embraces the universal love teaching, but he never explains how this can be compatible with just war. And even as he endorses universal love, Levering quotes from the Book of Revelations without considering the implications of the bloody warfare at the end of history prophesied in this last book of the New Testament (222).
Moreover, Levering is silent about the brutal violence of the Old Testament that has led the Catholic Church to indicate that the Old Testament cannot be a reliable text for moral teaching.
Levering's primary argument for the necessity of biblical revelation in supporting natural law is that only through such revelation can we see the ultimate explanation for natural law as rooted in God's creation of nature. But when we seek for ultimate explanations, aren't we forced back to one of two explanations? All explanation depends on some ultimate reality that is unexplained. The naturalist will say that all explanation presupposes the observable order of the natural world as the final ground of explanation that cannot itself be explained. The biblical believer will say that behind nature is nature's God. We must ultimately appeal either to an uncaused nature or an uncaused God. But either of these ultimate grounds of order will support natural law.
Some of these themes have been taken up in some previous posts, which can be found here, here, here, here, here, here, here, here, here, here, here, here, here., here, and here.
[In some later posts (in August of 2011), I have argued that Thomas Aquinas's teaching on natural law is rooted in Aristotle's biology, that this is particularly clear in Aquinas's biological account of the natural law of sex, marriage, and parental care, and that much of this biological reasoning for natural law can be confirmed by modern Darwinian biology. Levering is silent about Aquinas's reliance on Aristotle's biology.]
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