From THE DAILY MULL:
Are humans selfish by nature, or competitive, or fair?
Suppose you and another person participated in an exercise with two choices: either you receive five dollars, and the other person receives three dollars, or you receive seven dollars and the other person gets nine dollars? And suppose that you get to choose, all by yourself, every time?
Interestingly, there are three groups of results: People who want to win, and so choose less, as long as other player gets less still. People who are rational, and so choose more money, even if other player gets more. And (strangely) people who mix.
Dave Munger, COGNITIVE DAILY, on same topic, and root of thread.