Peter Singer has a new post, over at Project Syndicate, on the question, "Should We Trust Our Intuitions." In it, he refers to recent work in experimental philosophy by Josh Greene and Marc Hauser, both at Harvard.
There's an old chestnut in moral psychology known as the "trolley problem." Here's Singer's description:
In one dilemma, you are standing by a railroad track when you notice that a trolley, with no one aboard, is heading for a group of five people. They will all be killed if the trolley continues on its current track.
The only thing you can do to prevent these five deaths is to throw a switch that will divert the trolley onto a side track, where it will kill only one person. When asked what you should do in these circumstances, most people say that you should divert the trolley onto the side track, thus saving a net four lives.
In another dilemma, the trolley, as before, is about to kill five people. This time, however, you are not standing near the track, but on a footbridge above the track. You cannot divert the trolley. You consider jumping off the bridge, in front of the trolley, thus sacrificing yourself to save the five people in danger, but you realize that you are far too light to stop the trolley.
Standing next to you, however, is a very large stranger. The only way you can prevent the trolley from killing five people is by pushing this large stranger off the footbridge, in front of the trolley. If you push the stranger off, he will be killed, but you will save the other five. When asked what you should do in these circumstances, most people say that it would be wrong to push the stranger.
Standard apriorist philosophy often seeks to provide a theoretical underpinning to validate our intuitions -- that is, to provide a deeper explanation for why it is right to flip the switch but not to push the stranger onto the track. Greene and Hauser, however, are using research techniques from social psychology and neuroscience to provide a naturalistic explanation for our intuitions. Again, here's Singer:
Greene found that people asked to make a moral judgment about “personal” violations, like pushing the stranger off the footbridge, showed increased activity in areas of the brain associated with the emotions. This was not the case with people asked to make judgments about relatively “impersonal” violations like throwing a switch. Moreover, the minority of subjects who did consider that it would be right to push the stranger off the footbridge took longer to reach this judgment than those who said that doing so would be wrong.
Why would our judgments, and our emotions, vary in this way? For most of our evolutionary history, human beings – and our primate ancestors – have lived in small groups, in which violence could be inflicted only in an up-close and personal way, by hitting, pushing, strangling, or using a stick or stone as a club.
To deal with such situations, we developed immediate, emotionally based intuitive responses to the infliction of personal violence on others. The thought of pushing the stranger off the footbridge elicits these responses. On the other hand, it is only in the last couple of centuries – not long enough to have any evolutionary significance – that we have been able to harm anyone by throwing a switch that diverts a train. Hence the thought of doing it does not elicit the same emotional response as pushing someone off a bridge.
The lesson that Singer draws from this research is that
these findings should make us more skeptical about relying on our intuitions. There is, after all, no ethical significance in the fact that one method of harming others has existed for most of our evolutionary history, and the other is relatively new. ... And surely the death of one person is a lesser tragedy than the death of five, no matter how that death is brought about. So we should think for ourselves, not just listen to our intuitions.
I'm not as certain as Singer that, as a general rule, the evidence provided by our emotional responses to actual events or potential situations ought to be considered to be misleading as to whether it would be appropriate to bring about or prevent those events or situations. If Singer's evolutionary explanation of the particular responses to the trolley problem were correct, however, it would seem plausible to me that, in this case, the intuitions in question ought to be questioned -- as Singer says, "there is, after all, no ethical significance in the fact that one method of harming others has existed for most of our evolutionary history, and the other is relatively new."
I doubt, however, that the "personal"/"impersonal" explanation for the differing responses to the two cases is correct. Here's why. Suppose that one altered the second case so that, instead of pushing the large stranger off of the footbridge, you were removed from the situation, with access only to a switch that would allow you to move a crane so that the large stranger would be pushed off of the footbridge onto the track in the path of the oncoming trolley.
This, presumably, would make the second situation just as "impersonal," according to Greene's dichotomy, as the first situation. Nevertheless, my sense is that people would feel just as uncomfortable about pushing the large stranger off of the footbridge by flipping the switch and moving the crane as they would about "personally" pushing the large stranger off of the footbridge. If my hunch about this is correct, it would seem that the explanation of our intuitions in the trolley case has to appeal to something a bit more involved than the personal/impersonal dichotomy, at least as portrayed by Singer.