The study was done in two stages. A large group of Filipino men was studied in their 20s and again after 4.5 years. The second stage of the study found a dramatic fall of testosterone level among the men who found partners and became fathers.
Testosterone is associated with man's libido and aggression, and helps men find their mates and produce offspring. Lower levels help them become calm, attentive and evolve as a better father, the researchers found.
Earlier studies showed that fathers have lower levels of testosterone than childless men. To discover whether parenthood is directly involved with decline of manhood (that is, decline in the level of hormones), scientists studied the testosterone level of 624 Filipinos who were 21 years old.
They again studied them after most of the single men found their partners and became fathers. Research on them showed a drop of almost 34 percent in the testosterone level compared to single, childless men who had a natural decline of 12 to 14 percent. Fathers with newly born babies and men who spend more than three hours a day in rearing children, showed the most decline in their level of testosterone.
The study has been published in the Proceedings of the National Academy of Sciences journal.
There's something about being an active father that's contributing to these dramatic declines, said Lee Gettler, study leader and biological anthropologist at Northwestern University.
The dip in the testosterone level benefits men in the long run as high levels increase risk for prostate and testicular cancer, stroke and heart diseases, said researchers.