Recent research suggests that Craig Newmark might be on to something when he does things because they feel right. There is increased brain activity in the emotional centers during moral decision-making of a personal nature—for example, when imagining physically killing someone as opposed to flipping a switch to kill someone. But Singer would probably say that Newmark doesn't go far enough. "The fact that our moral intuitions are universal and part of our human nature does not mean that they are right," he says. I'm skeptical about Singer separating ethical reasoning from our evolution, from how it is lived, but that's the mental lab of philosophy.
Singer's reasoning matches with other research that New York Times science writer Dennis Overbye describes in an article on free will (Times Select). He writes that "the conscious mind is like a monkey riding a tiger of subconscious decisions and actions in progress, frantically making up stories about being in control."—the order of brain activity is action then decision, contrary to the traditional model.
Philosopher Daniel Dennett is not fazed by this reversal. Overbye paraphrases him:
...it is precisely our immersion in causality and the material world that frees us. Evolution, history and culture, he explains, have endowed us with feedback systems that give us the unique ability to reflect and think things over and to imagine the future.
That, Dennett believes, is what makes us moral agents.