Fatherhood Affects Testosterone

Harvard experts on how behavior changes physiology

The New York Times published a page-one report on September 12 detailing a startling new scientific discovery: the level of testosterone, the male hormone, declines after a man becomes a parent, and declines further the more the father is involved in childcare. In evolutionary terms, that means the male human body adapts to parenting behavior in a way that is conducive to nurturing offspring. The Times reported that the research “suggests that men’s behavior can affect hormonal signals their bodies send, not just that hormones influence behavior. And, experts say, it underscores that mothers were meant to have child care help.” The article cites Christopher Kuzawa, an anthropologist at Northwestern, the coauthor of the underlying research, which involved studying 600 men in the Philippines.

Times reporter Pam Belluck cited two Harvard-affiliated experts at length to explain the significance of the findings. Cowles professor of anthropology Peter Ellison, curator of human biology in the Peabody Museum, told her, “The real take-home message” is that “male parental care is important. It’s important enough that it’s actually shaped the physiology of men.”

“Unfortunately,” he added, “I think American males have been brainwashed” to believe lower testosterone means that “maybe you’re a wimp, that it’s because you’re not really a man. My hope would be that this kind of research has an impact on the American male. It would make them realize that we’re meant to be active fathers and participate in the care of our offspring.”

Ellison, former dean of the Graduate School of Arts and Sciences and a member of the department of human evolutionary biology, runs the Reproductive Ecology Laboratory, which researches reproductive physiology and the regulation of reproduction. (Read the Harvard Magazine review of his book On Fertile Ground.) Given the link between higher testosterone levels and the risk of incurring prostate cancer, he observed in the Times, “Fathers who spend a lot of time in fathering roles might have lower long-term exposure to testosterone,” thereby reducing their risk for that disease: a direct evolutionary benefit for helping care for their very dependent progeny.

In a subsequent interview published in the Boston Globe (September 19), Ellison expanded on his views as reported in the Times. "This study and others like it," he said, "have established the fact that men have reproductive states, just like women do. We’re used to thinking of women as having reproductive states: pregnancy, lactation, menstrual cycling or not. We also know that the amount of time a woman spends nursing children or not menstruating lowers her risk of breast cancer. The more time a man spends in low testosterone states over his life may [turn out to] influence his risk of diseases like prostate cancer or osteoporosis later in life." He characterized those male reproductive states this way: "One of them might be called ‘mating mode’ in which a man’s testosterone levels are high and his physiology is geared toward seeking mates. And another might be called ‘parenting mode,’ when his testosterone levels are lower and his physiology is geared toward being a better caretaker and provider and not being distracted by mate-seeking." In evolutionary terms, Ellison explained, "Humans have evolved to have mates that last for more than just one copulation or one season and to participate together in raising a family. I think we can realize that being a father is part of what evolution has equipped a male to do."

Sarah Blaffer Hrdy ’68, Ph.D. ’75, professor emerita of anthropology at the University of California, Davis, and an associate of the Peabody Museum—author of the bestselling Mother Nature and of Mothers and Others: The Evolutionary Origins of Mutual Understanding—also put the study in context for Times readers. Drawing on her research as a primatologist and social and biological anthropologist, Hrdy posed the question of whether only biological fathers are affected, or whether similar results would occur "if you have an uncle or brother or stepfather living in the household and they care for the baby?” (Hrdy received an honorary Doctor of Science degree in 2009, an occasion she celebrated with her multiple-Harvard-degreed husband, Dan, and their offspring and extended family members. Full disclosure: Hrdy is an Incorporator of Harvard Magazine Inc.)


Updated September 19, 2011.

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