When it comes to extramarital affairs, Tiger Woods may have raised the bar, but according to a new book on modern sexuality, the pro golfer may have been responding to a biological desire to "revive his staggering testosterone." In "Sex at Dawn: The Prehistoric Origins of Modern Sexuality" co-authors Cacilda Jetha and Christopher Ryan argue that men's testosterone levels begin to decline in their 20s, and one way they revive it is by meeting a new woman. In one instance, researchers found that even "a brief chat with an attractive woman raised men's testosterone levels by fourteen percent within minutes." For some men, this spike in testosterone may result in a brief affair, but some make a long-term commitment because of "the hormonal changes triggered by an affair with actual "love," thus leading them to make ill-advised decisions catastrophic to their families, their marriages, and eventually themselves." In Woods' case his philandering destroyed more than his marriage; it also tarnished his image and career.