Developmental Graduate Student Patty Kuo

I hate to break it to you, but if you are reading this and happen to be human, you’re subject to the vicissitudes of testosterone.  The fact that your thoughts and behavior are even in the slightest way influenced by a hormone generated primarily by the gonads may challenge your most basic sense of self.  But despair not, reader.  Testosterone, or simply T, doesn’t necessarily reduce a person to base instincts and/or Hulk-like, destructive fits of rage.  Researchers argue it can have a positive and useful place in our lives, particularly in the contexts of romance and work — or more generally, those areas of life where competition rules supreme.

Having said that, I should mention that our relationship with T begins long before we land our first job or even our first kiss.  Indeed, it quietly starts shaping our lives while we’re still in the womb, and you can find traces of this early exposure carved into your hands; those of us exposed to higher levels of testosterone are more likely to have longer ring fingers than index fingers — the difference being especially pronounced in men.  And while it’s not an exact science, this so-called 2D:4D digit ratio can predict a number of things about who we are as individuals — both physically and personality-wise.

When I spoke with Lee Gettler, the Director of Hormones, Health, and Human Behavior Lab at the University of Notre Dame, he confirmed that prenatal testosterone “can have modest impacts on neural development,” which may go on to influence a person’s behavior and cognition long after birth, but Gettler cautioned that the literature is “pretty mixed.”

However significant, these changes are what Jim Roney with the Department of Psychological and Brain Sciences at the University of California, Santa Barbara refers to as “organizational effects.”  Being that they are developmental in nature, the effects of prenatal testosterone are essentially fixed, but over the course of a lifetime, T levels become much more fluid and its effects “temporary and reversible, like turning a switch on and off,” Roney tells me.

So, what flips on the switch?


But what about partners who are satisfied with their relationship — or at least long enough to have a child?“My prior longitudinal research on new fathers’ testosterone changes showed that the transition to fatherhood caused new dads’ testosterone to decline on average,” explains Gettler, adding that new fathers with lower testosterone “tend to be highly involved with caring for their children and are more sensitive to their cues.”

Gettler’s findings have been recently corroborated by a study led by the University of Michigan.  Halfway through the experiment, participating fathers were asked to observe their one-year-old babies cry from behind a two-way mirror, and researchers found that compared to their T levels at the start of the study, fathers experienced a drop in testosterone upon seeing their children in distress.  Interestingly, researchers also observed that these lower levels were associated with more positive parenting styles.

“We think that the decreases in testosterone in response to seeing your baby cry seems to help promote sensitive, nurturing care,” says Patty Kuo, the paper’s first author.


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