A spike in testosterone may not always turn you into a greedy, aggressive, power hungry monster. According to research led by Ernst Fehr, testosterone's true effect may be to encourage status-seeking behavior, and it can actually make people play more fairly with others. What's more, its biological effects on a person may be overruled by that person's beliefs. In a game-playing experiment set up by Fehr in which some people received a testosterone shot while others got a placebo,