5. Men with a lot of testosterone do weird things with money.

Neoclassical economists have often argued that people will naturally seek financial gain, no matter how small, and will do so in a rational manner.  But psychologists have found otherwise. 

The Economist magazine describes an ultimatum game in which one player divides a pot of money between himself and another. The second player then chooses whether to accept the offer. If he rejects it, neither player benefits. Curiously, a low offer is usually rejected, despite the fact that rejecting the offer means that the players will get zilch.

Terence Burnham of Harvard University observed male players and compared their testosterone levels using saliva samples. Turns out that the ones who refused a stingy final offer had an average testosterone level more than 50 percent higher than the average of those who took it. The reason appears to be that the high testosterone people would rather accept less themselves than see a rival get ahead. They seem to be programmed to seek social dominance, and they will behave irrationally trying to get it.