I just finished reading a recent article by Peter Singer discussing the research findings of, among others, 3 very interesting researcher: Jonathan Haidt, J.D. Greene, and, to a lesser extent, Antonio Damasio. The question that these researchers seek to ask is perhaps the central question of moral psychology: Why do we think the way we do about ethics?
[Singer's article is highly, highly worth reading (as is the work of these researchers), and if you'd like a copy of the pdf, let me know and I can send it to you. Or you can look it up yourself: Singer, Peter. "Ethics and Intuition." The Journal of Ethics (2005) 9: 331-352.]
Investigate the details for yourself, but the basic findings have been thus: for most people, ethical judgments based on emotional reactions (i.e., "intuitions") precede the justifications for these judgments, which are usually ad hoc rationalizations. In those people who rely more on rational considerations, they tend to have the same emotional reactions, but don't employ them. Instead, they spend time reasoning--it's been shown that they take longer to produce a judgment--before they articulate a judgment.
So that's step 1 of the argument: moral intuitions play a major role in our ethical lives. So why do we have the intuitions that we do? The short answer is evolution within a social context. For a longer answer, see Singer's article.
Singer, who wisely disparages attempts by people to turn survival of the fittest into a norm, now goes beyond the question of origins, asking a version of Korsgaard's "normative question": why should we trust our intuitions if they developed merely as a response to certain selective pressures that our anecestors faced? In essence, this is a refusal to accept "natural" as a more characteristic--there is no intelligible conception of it that is consistent and, as my colleague Jeff has pointed out, invocation of the word is often an excuse to ignore other people's points of view.
The conclusion that Singer reaches is that we have no reason to trust our intuitions, knowing what we know, no reason to apologize for evolution's "nature red in tooth and claw," the blind, slow and gruesome process of trial and error that allowed us to be the beings we are today only through a great cost of suffering.
An implication of this is that views which appeal to moral intuitions as a basis for ethics, such as Rawls' use of "reflective equilibrium," are extremely questionable. Singer suggests that there is no reason to even factor intuitions into ethical decisions, that they observe absolutely no weight.
This also flies in the face of Bernard Williams' view about avoiding theory in ethics. The justification he provides for this is largely an intuitive one. But why trust those intuitions? They are not merely given, but are open to question. History is full of unquestioned prejudices which could only be dissolved after being put to the test.
That's all I'll say for now. Singer's article includes the beginnings of a response to those who think that we need some intuitions, such as that pain and death are bad, even if we're utilitarians. I think it's more difficult than this, but I find myself tending to side with Singer here. Socrates was constantly going around and getting people to examine their core intuitions.
Should not ethical philosophy, while employing moral psychology for therapeutic purposes (that is, only by recognizing our natural limitations and by training, building new habits, can we become better people), nevertheless be practiced in a similar critical way?