Testosterone enhances competitiveness and dominance, reduces fear and is associated with risky behaviour like gambling and alcohol use. Men have more testosterone than women and a study of M.B.A. students has shown that only 36% of female students go into high-risk careers such as trading or investment banking compared to 57% of male students. Researachers from the Kellogg School of Management at Northwestern University in Illinois and the University of Chicago measured testosterone levels and risk-taking in around 500 M.B.A. students. Risk-taking was measured by a computer game in which the participants could either bank a relatively small amount of money or take part in a lottery to win a much larger amount. Overall men were much more likely than women to take risks and had significantly higher levels of testosterone. Higher levels of testosterone were associated with a greater appetite for risk in women, but not in men. Men and women with similar levels of testosterone had similar levels of risk-taking. When the participants were followed up after their course finished those who were high in testosterone and low in risk aversion chose riskier careers in finance.

You can find out more about this research at

http://www.sciencedaily.com/releases/2009/08/090824151254.htm