Married life is stressful, as any stand-up comedian or therapist will tell you. But being married or in a long-term relationship can also change not only your mood, but also your hormones and behavior as well. Biologists have known for a while that when male birds or monkeys stop mating and start raising offspring, they experience a large drop in testosterone. Now, in a recent study published in the journal Stress, researchers find that this may also happen in an advanced kind of primate: University of Chicago business school students.
The study was originally designed for an entirely different purpose: correlating hormone levels with financial risk-taking behavior in students training for a career in business. A collaboration between Dario Maestripieri, a professor of comparative human development at the University of Chicago, and two business school professors (Luigi Zingales of UChicago’s Booth Business School and Paola Sapienza of Northwestern’s Kellogg School of Management), the project used 500 Booth students as their subjects. The students were asked to play a series of computer games that tested economic decision-making, and saliva samples were taken before and after the test to assess hormone levels and changes.
A primary finding of the study, published last year in the Proceedings of the National Academy of Sciences, was that testosterone levels correlated with risk-taking behavior – students with high baseline testosterone were more likely to take chances in a lottery-style game. The result explained away the commonly observed gender difference in risk-taking, as men have much higher average testosterone levels than females. Published in the middle of the financial crisis, media outlets ran with the implication that the recession might have been avoided if more women had been in charge of our banks and trading firms.
“It’s clear that there are sex differences in aggressiveness and violent behavior – look at who commits all the murders, who fights all the wars,” Maestripieri said. “On average, males are clearly more aggressive, more violent, and take more risks than women, and this affects society and also business. If business is male-dominated, things are going to be done a certain way and if business were female-dominated, things probably would be done differently.”
Aside from assessing the students’ financial behavior, the test also provided the opportunity for an experiment on stress. The students were told that the test was required for a course and would impact future career placement, a scenario designed to inspire both honesty and stress. That allowed researchers to look for effects on cortisol, often called the stress hormone. Cortisol is traditionally a tricky hormone to measure, due to wide variation in its changes between people – and even within the same person – when faced with a stressful stimulus. But the large size of this project helped get around that problem.
“As far as I know, this is the largest study ever done that has looked at the hormonal effects of psychosocial stress,” Maestripieri said. “I think it clarifies some things that were not very clear in the stress literature.”
On average, the study found that women experienced larger surges in cortisol when measured after the stressful test, while men showed a larger test-induced decrease in testosterone. But the more interesting difference went beyond gender to another factor: relationship status. Male subjects who were not married or in a long-term relationship had higher average levels of testosterone, corroborating several previous observations. But they also responded differently to the stress of taking the test, with larger increases in cortisol compared to men in a committed relationship.
“Although marriage can be pretty stressful, it should make it easier for people to handle other stressors in their lives,” Maestripieri said. “What we found is that marriage has a dampening effect on cortisol responses to psychological stress, and that is very new.”
The finding that single males have higher testosterone mirrors hormonal observations previously made in studies of our primate relatives, noted Maestripieri, who conducts most of his research on rhesus macaque monkeys in Puerto Rico. Fluctuations in testosterone are observed in males of many species, with peaks of the hormone occurring when males fight other males and take risks to attract females. Because males have a wider variation in reproductive success – males can impregnate hundreds of females in a lifetime, while females are only able to have a small number of offspring – nature favors the bold.
“In a lot of different species – monkeys, other mammals, birds – males are more often the risk-takers, because they have more at stake and they have more to gain by taking risks,” Maestripieri explained. “Males don’t live as long as females; they live in the fast lane where they can be very successful but then because of all this risk-taking they usually die young.”
But in species that show monogamous pairing and shared raising of offspring between males and females, testosterone levels in males drop as they engage in more fatherly behavior. In humans, the connection between testosterone and marriage has a chicken-and-egg problem; it’s not clear whether marriage and fatherhood lowers testosterone, or whether men with lower testosterone are more likely to get hitched. But the new study’s findings suggests marriage might have an additional hormonal role: protecting married students from being as psychologically and physiologically stressed by a test relative to their single peers. Thus, for students, settling down might be a good strategy for settling down.
Maestripieri, D., M. Baran, N., Sapienza, P., & Zingales, L. (2010). Between- and within-sex variation in hormonal responses to psychological stress in a large sample of college students Stress: The International Journal on the Biology of Stress DOI: 10.3109/10253891003681137