A few months ago, government researchers released the latest American Time Use Survey. It included the average time per day that Americans spent providing child care between two thousand six and two thousand ten. Among adults living with children under age six, women spent one hour and six minutes a day providing physical care like bathing or feeding. Men spent twenty-six minutes. Yet a new study suggests that men are biologically designed to care for their children. It confirmed that testosterone levels drop after men become fathers. Testosterone is the main sex hormone responsible for the changes when a boy develops into a man. Women also produce testosterone but in much lower amounts. Earlier studies showed that fathers have lower levels of testosterone than childless men. Christopher Kuzawa at Northwestern University in Evanston, Illinois, says there are at least two possible explanations: "Is it that fatherhood reduces your testosterone? Or do men with low testosterone to begin with, are they more likely to become fathers? And so what we did is, we followed men through time and measured their hormones before and after they became fathers."The researchers used findings from a long-term study of men in the Philippines. Their testosterone levels were measured in two thousand five and two thousand nine. Some of the men were childless; others became fathers during that time. And those were the men where the researchers saw the largest decline in testosterone.The study found that levels dropped by about half immediately after the birth of a child, then rose some. Men who were active in child care produced less than those who were not active. Testosterone may drop in fathers to get them to pay more attention to parenting than to reproducing. But Professor Kuzawa says there are other good reasons as well: "Having high levels of testosterone can increase your risk for diseases like prostate cancer [and] testicular cancer." The study is in the Proceedings of the National Academy of Sciences. Studies have shown a similar drop in other mammals and in birds after mating periods to allow for care giving. Animal studies have also shown that the greater the involvement of males, the lower their testosterone levels.We asked Thomas McDade, another author of the study, if levels also drop in men who adopt children. That is an interesting question, he says, and the "next obvious thing to study."

For VOA Special English, I'm Carolyn Presutti.