ABSTRACT: A familiar position regarding the evolution of ethics is that biology can explain the origin of morals but that in doing so it removes the possibility of their having objective justification. This position is set fourth in detail in the writings of Michael Ruse (1986, 1987, 1989, 1990a, 1990b) but it is also taken by many others, notably, Jeffrie Murphy (1982), Andrew Oldenquist (1990), and Allan Gibbard (1990). I argue the contrary view that biology provides a justification of the existence of morals which is objective in the sense of being independent of people's moral views and their particular desires and preferences. Ironically, my argument builds on the very premises which are supposed to undermine the objectivity of morals. But my argument stops short of claiming that biology can give us a basis for justifying some particular system of morals. Drawing on an analogy with social contract theory, I offer a general reason why this more ambitious project cannot be expected to succeed if the argument is pursued along the same lines. Finally, I give reasons why the possibility of objective justification for a particular morality cannot be ruled out in general on evolutionary grounds.

KEY WORDS: Morality, evolution, justification, objectivity.

1. HOW DID MORALS EVOLVE?
This is a good question to which there is no sure answer. What has emerged over the past several decades is a collection of "just so stories" which are consistent with current biological theory. These accounts characteristically are coupled with a non-cognitivist reading of moral judgment. Not to beg any questions, let me assume with Ruse, Murphy, Oldenquist, and Gibbard that moral beliefs can be identified as such without presuming that they refer to or correspond to a realm of moral facts. What makes them moral beliefs, let us assume, is how they function with respect to guiding deliberation and motivating action. In particular, let us say (following Brandt 1979) that beliefs are moral when they share the following features: they intrinsically motivate certain actions or omissions, occasion feelings of guilt when this motivation is deficient, occasion admiration and esteem for others when they have an abundance of this motivation, and elicit the thought that having this motivation is important enough to warrant imposing sanctions against those who are deficient in it. Moral beliefs are from this perspective essentially dispositions to think, feel, and act in accordance with certain norms. The next step in giving an evolutionary account of morals is to link this dispositional account of moral belief with natural selection. Suppose that these dispositions are heritable and fitness enhancing. Then we have the basic ingredients for a Darwinian story of how natural selection favours the preservation and refinement of such dispositions from one generation to the next - in short, the evolution of morals. Would such dispositions be fitness enhancing? The moral prohibition against incest is perhaps the most frequently cited example where this assumption seems reasonable, since avoidance of incest (at least prior to the advent a sophisticated methods of birth control) is biologically adaptive in strict Darwinian terms. But prohibitions against murder, assault, stealing, and breaking one's word are arguably fitness enhancing as well, for humans have on average more to lose in terms of fitness when they are subject to these wrongs than they have to gain as perpetrators. In sum, natural selection would appear to favour what we can call a common core of moral inhibitions, which we now express in the form of general moral beliefs about what we ought to do and not do.