It’s the testosterone, don’t you know. Years ago when I was conducting my doctoral research on the evolutionary history of men among a remote indigenous community of hunter-gatherers living in the forests of South America, I came across a man donning a well-worn baseball cap likely donated by missionaries. The cap read, “There are three stages to a man’s life: Stud, Dud, Thud.” Indeed. It is somewhat sobering to see one’s life’s research summarized on a piece of headwear that can probably be found for a few dollars at a roadside truck stop. But such is the elegance of interesting science. It’s no secret that mortality due to accidents and risky behavior is much higher in young men, particularly those in their late teenage years and early 20s. This, by the way, is not news to insurance companies. It’s also true that men die earlier than women, regardless of their environment or lifestyle, and are often more susceptible to some cancers and heart disease at an earlier age. In fact, men are at a higher risk than women when it comes to most of the top 15 contributing sources of mortality in the United States—which account for nearly 80 percent of all deaths. In the words of a Yale evolutionary biologist, “Macho makes you sick.” Evolutionary factors are clearly at play. The question is why. What is natural selection’s deal with men? It’s a compelling academic question, for sure. But now that I’m in my 50s, I have to admit the issue of aging gets more relevant with every new gray hair. As it turns out, shorter lifespans and higher male mortality risk are quite common in many species. Natural selection doesn’t necessarily favor traits commonly associated with health, vigor, and longevity. Instead, it promotes characteristics that provide greater lifetime reproductive success, or in the parlance of evolutionary biology, fitness. If the benefits of increased fitness are greater than the cost of a shorter lifespan or poor health, biology will prioritize those traits. In essence, sex trumps birthday candles. This tradeoff between longevity and reproduction takes an obvious form in women: Pregnancy, childbirth, and lactation are all physically taxing and energetically costly. Research has shown that bearing more children is associated with higher oxidative stress, which can in turn lead to accelerated aging in post-menopausal women.1 A 2006 historical study of rural Polish women, for example, found a correlation between having more children and a significantly shorter post-menopausal lifespan.2 Although more research needs to be done, it would seem that reproductive effort can literally take years off your life. ? FATAL ATTRACTIONMale quolls (above) experience a dramatic one-time rise in testosterone that triggers intense bouts of mating—and very high mortality.