Some excerpts from Time magazine's currentarticle on ambition:
From a Washington University study looking at persistence, "In general, the researchers found that students who scored highest in persistence had the greatest activity in the limbic region, the area of the brain related to emotions and habits. "The correlation was .8 [or 80%]," says professor of psychiatry Robert Cloninger, one of the investigators. "That's as good as you can get."
Also re: one Stanford- U Pittsburgh study involving competition, "Men and women performed equally in both tests, but on the third round, when asked to choose which of the two ways they wanted to play, only 35% of the women opted for the tournament format; 75% of the men did."