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The publication in 1975 of Edward O. Wilson's Sociobiology provoked a great controversy. Our deepest intuitions of right and wrong, Wilson asserted on the first page of his book, are guided by the emotional control centers of the brain, which evolved by natural selection to help the human animal exploit opportunities and avoid threats in the natural environment. Ethics is a branch of biology. The publication last year of Wilson's Consilience renewed the controversy as he continued to argue for explaining ethics through the biology of the moral sentiments.

Wilson's critics have warned that his reductionistic explanation of human ethics as a mere expression of animal impulses promotes a degrading view of human life. Some of his Christian critics have explained this as an inevitable consequence of a scientific naturalism that denies God's moral law as the supernatural ground for our sense of right and wrong. And yet I think Wilson's position is much stronger than it might seem at first glance. Indeed, the full strength of Wilson's Darwinian ethics becomes clear only when it is seen as a form of ethical naturalism that belongs to a tradition of natural law reasoning that is compatible with Christian theology.

The biological character of the natural moral law is suggested by a famous remark by Domitius Ulpianus, an ancient Roman jurist: "Natural right is that which nature has taught all animals." As quoted at the beginning of Justinian's Institutes, this remark entered the tradition of natural law reasoning, and it was cited by Thomas Aquinas when he explained natural law as rooted in "natural inclinations" or "natural instincts" that human beings might share with other social animals. Adam Smith continued this tradition of thought in explaining ethics as expressing the moral sentiments of human nature. As influenced by Smith's ethical theory, Charles Darwin explained the moral emotions as manifesting a moral sense rooted in the biological nature of human beings as social animals. As influenced by both Smith and Darwin, Edward Westermarck defended a view of ethics as founded in moral emotions shaped by natural selection in evolutionary history. Wilson recognizes that his biological theory of the moral sentiments belongs to a tradition of ethical naturalism that includes Smith, Darwin, and Westermarck. But he does not recognize the roots of that tradition in the natural law reasoning of Aquinas and other Christian philosophers.

Uncovering the common ground between Wilson and Aquinas should make it easier for Christians to come to terms with Wilson's expansive claims for scientific knowledge. Rather than completely rejecting Wilson's Darwinian view of ethics, Christians can adopt some of Wilson's reasoning to strengthen the case for natural law by finding support for it in Darwinian science.

Wilson's explanation of ethics as rooted in human biological nature is a crucial part of his larger project in striving for "consilience" in human knowledge. He adopts the term consilience for the idea that nature is governed by a seamless web of causal laws that cross the traditional disciplines of study. He appeals to "a belief in the unity of the sciences—a conviction, far deeper than a mere working proposition, that the world is orderly and can be explained by a small number of natural laws." Against the fragmentation of knowledge into apparently unrelated do mains, Wilson argues for linking the natural sciences, the social sciences, and the humanities in the common effort to explain everything through the universal laws of nature.

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