What do these lower testosterone levels mean for the men? It's hard to say. "I don't think it makes them less tough or less masculine," Gettler said. "It might make them more attuned to the needs of their kids and less oriented toward competing with other men outside of the family context, whether that means competing with other men for the attention of women or engaging in risky behavior."
Testosterone levels dipped even lower in men who directly helped take care of their kids. "Our assumption is that there's something about physically interacting with their kids, whether it's through sight or smell or physical touch, that activates something in the brain of men and has this trickle-down effect," Gettler said.
Richard G. Bribiescas, chair of anthropology at Yale University, said lower testosterone levels could "be a side effect of increasing bonding hormones such as oxytocin and prolactin. Lowering one's testosterone may also bolster a male's immune system and thereby decrease the possibility of passing along pathogens and infections to newborns whose immune systems are still developing."
Robert J. Quinlan, an associate professor of anthropology at Washington State University, said the study raises the question of whether testosterone levels don't drop in men who end up having poor relationships with their children. "One might manipulate the system by encouraging fathers to get the early experience with children that lowers testosterone levels, and then perhaps family stability and child outcomes would improve," he said.
The study appears in this week's online edition of the Proceedings of the National Academy of Sciences.
For more about testosterone, try the U.S. National Library of Medicine.
SOURCES: Lee T. Gettler, Ph.D., graduate studen
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