"Thomistic Natural Law as Darwinian Natural Right" by Larry Arnhart, in Social Philosophy & Policy (Winter 2001), Social Philosophy and Policy Center, Bowling Green State Univ., Bowling Green, Ohio 43403.

In his controversial works Sociobiology (1975) and Consilience (1998), Edward O. Wilson argued that ethics is rooted in human biology: the deepest intuitions of right and wrong are guided by the brain’s emotional control centers, which evolved through natural selection to help the human animal exploit opportunities and avoid threats in the environment.

Many critics contend that Wilson’s explanation of human ethics promotes a degraded view of human life. Some religious critics deplore it as a denial of God’s moral law as the basis for human ethics. But Arnhart, a political scientist at Northern Illinois University, argues that the Harvard University scientist belongs to the same tradition of ethical naturalism as Thomas Aquinas. Indeed, Wilson’s Darwinian view of human nature, in Arnhart’s view, lends support to Aquinas’s "natural law" reasoning.

Drawing on Aristotle’s biological psychology, Aquinas (1225–74) "explained natural law as rooted in ‘natural inclinations’ or ‘natural instincts’ that human beings share with other intelligent animals," notes Arnhart. Thus, as with other animals whose offspring require care from both parents, Aquinas said, nature implants in the human male and female an inclination to stay together. Unlike other such animals, humans—using their unique cognitive capacity for conceptual reasoning—devised customary or legal rules of marriage, in conformance to natural law, thus giving formal structure to their natural desires.

Starting in the 17th century with Thomas Hobbes, says Arnhart, there was a modern break with "the Aristotelian and Thomistic account of natural law as rooted in the biology of human nature." Hobbes insisted "that social and political order is an utterly artificial human construction," not rooted in biology but requiring that humans transcend their animal nature.

In the 18th century, however, says Arnhart, there was, in effect, "a revival of the Thomistic conception of natural law as founded in the inclinations or instincts of human nature." Adam Smith showed "how ethics and economics could be rooted in the moral sentiments of human nature and the natural inclination to sympathy." In the next century, Charles Darwin "explained the moral sentiments as manifesting a moral sense rooted in the biological nature of human beings as social animals." He argued that natural selection implanted in humans the natural inclinations that lead to the moral sentiments. Adding comparative data on social behavior to Darwin’s and Smith’s ideas, sociologist Edward Westermarck (1862–1939) defended a theory of ethics "rooted in the natural moral sentiments," says Arnhart. The nearly universal incest taboo, for example, worked via an emotional aversion favored by natural selection.

"While Wilson recognizes that he belongs to a tradition of thought that includes Aristotle, Smith, Darwin, and Westermarck," Arnhart notes, "he explicitly rejects Aquinas’s views" because they seem to him to root ethics in absolute moral standards outside humanity. But though Aquinas regarded natural law as ultimately an expression of God’s will, says Arnhart, he distinguished "the natural law, as known by the human mind’s grasp of the natural inclinations, from the divine law, as known by God’s revelation of His will through the Bible." Marriage, for instance, has both sacred and secular meanings, and the secular one is quite compatible "with Wilson’s ‘empiricist’ view of morality." Similarly today, Arnhart concludes, the religious believer and the Darwinian scientist "can each look to the laws of nature as a ground of common human experience that can be known by natural reason alone."