Results of a study done by a team of Harvard University anthropologists increase our knowledge of human biology — and may have implications for so-called “male menopause.” Researchers have long suspected that levels of testosterone — the hormone largely responsible for fighting, competing, and mating — decrease when men settle down and start a family. Other studies have shown that testosterone begins to decline shortly after marriage, but surges upward when unions end in divorce. “It makes sense,” notes Peter Ellison, professor of anthropology. “Lower levels of testosterone may increase the likelihood that men will stay home and care for their wives and kids, while decreasing the likelihood they will go out drinking with the guys and chase other women.” To pin down precisely how hormones vary between single men, married men without children, and married men with children, graduate student Peter Gray and his colleagues tested a total of 58 men in the three categories. Testosterone can easily be measured by analysis of saliva. The analyses showed little difference between married men with and without children, but both had significantly lower testosterone levels than unmarried fellows.