You might have encountered the Trolley problem:

A trolley is running out of control down a track. In its path are 5 people who have been tied to the track by a mad philosopher. Fortunately, you can flip a switch which will lead the trolley down a different track. Unfortunately, there is a single person tied to that track. Should you flip the switch?

It seems obvious to most people that you should. (Don't fret if you disagree -- so do I.) But what if we change the scenario:

As before, a trolley is hurtling down a track towards five people. You are on a bridge under which it will pass, and you can stop it by dropping a heavy weight in front of it. As it happens, there is a very fat man next to you - your only way to stop the trolley is to push him over the bridge and onto the track, killing him to save five. Should you proceed?

Polls find that most people think this is not permissible. Indeed, the high degree of agreement among people's intuitions about these problems has led to the speculation that they may be revealing the facets of an intuitive morality instinct/module/faculty.

Now consider this (related) item from the recent pol poll: "The life of one American is worth the lives of several foreigners." Operationally, we tend to act as if this were our belief. However, you may (like me) find this to be an uncomfortable admission. (If you don't, perhaps the graphic images in Nick Gillespie's latest piece in Reason will change your mind [warning: graphic image].) Philosopher Peter Singer has done work on this subject. He offers a "Cosmopolitan" utilitarian ethic, which I don't find compelling enough.

Update: Good comments. BTW -- Bryan Caplan's comments on Ethics and IQ is what sparked this musing about moral intutions. In particular, Caplan claims that "One of our most basic moral intuitions is that people who succeed because of their personal ability deserve what they have." Sure about that?

Update 2: From the comments: an article by Carl Zimmer that details this topic.