A new study by researchers at Northwestern University shows that fathers may be biologically wired to be more nurturing after marriage and children. The study is titled “Longitudinal Evidence That Fatherhood Decreases Testosterone in Human Males” was published in the September 12, 2011 issue of the Proceedings of the National Academy of Sciences (PNAS).
The study looked at 624 males aged 21.5 to 26 years old for 4.5 years in the Philippines. The researchers found that the men, before they were married, had normal levels of testosterone, the primary male sex hormone. After the men were married, the researchers found that the testosterone levels of the men had dropped, and when the man smelled his own child his testosterone level dropped even further.
Christopher W. Kuzawa, co-author of the study and associate professor of anthropology in the Weinberg College of Arts and Sciences said, “Humans are unusual among mammals in that our offspring are dependent upon older individuals for feeding and protection for more than a decade. Raising human offspring is such an effort that it is cooperative by necessity, and our study shows that human fathers are biologically wired to help with the job.”
According to the AFP, men who became fathers during the study showed a median 26 to 34 percent drop in testosterone levels, while the normal age-related drop in testosterone in single men who were not fathers was 12 to 14 percent. The steepest decline of the hormone was in fathers of newborns less than one month old.
Lee Gettler, a co-author of the study, says that “Fatherhood and the demands of having a newborn baby require many emotional, psychological and physical adjustments. Our study indicates that a man´s biology can change substantially to help meet those demands.”
Having lower testosterone levels may not be as bad as it sounds. According to the New York Times, some experts believe that the hormone study could offer new insight into men´s medical conditions, particularly prostate cancer. Higher levels of testosterone over a lifetime show an increase in a man´s risk of prostate cancer, much like a woman´s increase in estrogen levels shows an increase in breast cancer.
Dr. Peter Ellison, a professor of human evolutionary biology at Harvard, who was not involved in the study, told the New York Times, “Fathers who spend a lot of time in fathering roles might have lower long-term exposure to testosterone, reducing their risk.”
Men should be reassured though that these hormonal changes may be dramatic and not drastic. Dr. Carol Worthman, an anthropologist from Emory University also uninvolved with the study, told the New York Times, “If guys are worried about basically, ℠Am I going to remain a guy?´ We´re not talking about changes that are going to take testosterone outside the range of having hairy chests, deep voices and big muscles and sperm counts. These are more subtle effects.”
MSNBC notes that there is research done with primates that when they smell their own children their testosterone levels drop within minutes. This could be the body´s way of protecting the young by lowering aggressive behavior so the father doesn´t become rowdy and cruel around the kids and possibly attack them.
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