I just went to an APA session on evolution and meta-ethics, where one of the speakers was Sharon Street. A question that repeatedly came up was: do evolutionary debunking arguments (EDAs) against moral objectivism enjoy a special status? Differently put: Does the theory of natural selection as applied to our evaluative judgments add anything more that is not found in other types of debunking explanations (e.g., sociological or cultural explanations)?
During the Q&A, Street said that she thought there is nothing in particular about evolutionary explanations that should worry the moral objectivist; we can use any sort of causal genealogy to argue against moral objectivism. The focus on evolutionary theory, rather than say, sociology, or cultural anthropology, in debunking arguments against moral objectivism is a consequence of evolutionary theory's 'universal acid' properties (to use Dennett's term): evolutionary theory, presumably more so than other scientific theories, provides us with a very plausible story of why some moral evaluative judgments recur cross-culturally (e.g., "nurturing your children is right", "cheating on those who have helped you earlier is wrong", etc.). An additional strength of evolutionary theory that Street proposed was that, even if there were universal agreement about moral evaluative attitudes, this would not constitute any evidence for moral objectivism, because an evolutionary account can plausibly of why we hold those beliefs without invoking any objective moral norms. Indeed, it would be highly unlikely, an incredible coincidence, if this were the case (this is an important element in Street's 2006 PhilStudies paper).
Yet there seems to be an intuition that there is something about evolutionary theory that is special - the universal acid bites harder and deeper than other explanations (such as appeals to cultural influence in earlier decades?) Is there something about evolutionary theory that makes it off-track? Now, as Street acknowledged, not all genealogical accounts are debunking. In some cases, knowing something about the origin of particular beliefs increases their epistemic standing. In such cases, there is a connection between a belief and its truthmaker that figures in the explanation. And this, according to anti-realists about morality, is not the case. We need no independent moral truths to figure in our explanation of why we hold moral beliefs at all.
By contrast, according to Street (and other anti-realists for moral norms, like e.g., Griffiths & Wilkins, 2010), the case is different for commonsense beliefs. She says (not an exact quote, but drawn from memory): we believe in the existence of rocks, tigers and stuff, because it is fitness-enhancing for us to believe in the existence of these things, and this is because predators, inanimate object, etc. do play a role in our evolutionary history. Interestingly, Griffiths & Wilkins think that there are also good evolutionary reasons to assume that scientific beliefs are true (I won't go into them here). The point I want to make is this: evolutionary arguments are special, since they are sometimes used to debunk beliefs (e.g., religious beliefs, moral intuitions) and sometimes to vindicate beliefs (e.g., commonsense beliefs). Indeed - in parallel to the quickly expanding literature on evolutionary anti-realism we can find a quickly expanding literature on evolutionary arguments for the reliability of perception, the trustworthiness of induction, etc (see here for a recent example I co-wrote). This is in stark contrast to toy examples we often see in the literature, which are almost always uniformly debunking, regardless of the beliefs that are being debunked. For instance, Knowing that someone's belief that p was caused by a belief-that-p-inducing-pill leads one to reassess one's confidence in the belief.
As far as I know, there are very few evolutionary moral objectivists - I only know one such author, and that is Scott M. James. In his recent book An introduction to evolutionary ethics, and some recent papers he argues that the truth-value of our belief in moral norms does figure in the explanation of why we hold such beliefs, in particular, (quote from the abstract of his paper in PPR, 2008): "The sorts of adaptive pressures facing early humans would have produced more than just potent prosocial emotions, as evolutionary antirealists like to claim; it would have produced judgments—often situated within emotions—to the effect that others could reasonably disapprove of some bit of conduct, for an early human who cared deeply about how others might respond to her action enjoyed the benefits of more cooperative exchanges than those early humans who did not."
In response to this, Street may argue that these supposed truths are matters of fact and not norms (it may be bad for our ancestors if their reputation is ruined, but that doesn't say anything normatively about what they ought to do) . If this is the case, I think the prospects for an evolutionary-informed moral objectivism are grim, for here we stumble on the problem of the familiar Humean is/ought gap. But if this is a stumbling block for evolutionary-informed genealogies of norms, it will also be a stumbling block for other naturalistic genealogies of norms (e.g., cultural, social): how could any naturalistic genealogy - which is concerned with the causal, natural processes that influence our moral evaluative attitudes bridge this gap? It seems then that as we offer a plausible causal story of moral norms, we will be unable to make mind-independent moral truths figure in the explanation.
To conclude: I think there is something special about evolutionary genealogical explanations, since they are sometimes used to vindicate, and sometimes to debunk. But with respect to moral norms, there is no difference between evolutionary and other naturalistc (e.g., cultural) genealogies, because naturalistic genealogies cannot appeal to moral truths to explain the moral norms we have.