Babies Cut Dads' Testosterone That makes men better parents, researchers believe By Mary Papenfuss, Newser User Posted Sep 13, 2011 2:30 AM CDT Updated Sep 13, 2011 5:34 AM CDT 13 comments Comments New dads experience a substantial reduction in testosterone with the birth of a son or daughter, scientists have discovered. (?Rietje Swart) (Newser) – Who knew newborns could have such a significant physical impact on their dads' bodies? Scientists have discovered that fathers experience a significant reduction in their body's testosterone with the birth of a son or daughter. They believe it's Mother Nature's way of making men less interested in things like fighting and flirting, and more likely to be a nurturing parent and loyal spouse. Men with babies less than a month old showed the most significant reduction of testosterone, the study found. "Raising human offspring is such an effort that it is co-operative by necessity, and our study shows that human fathers are biologically wired to help with the job," said lead researcher Christopher Kuzawa of the Northwestern University study. "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." The scientists also believe lower testosterone levels may help men fight chronic disease, helping them to remain healthy fathers, reports the BBC.