Romantic partners who spend a weekend practicing childcare with a lifelike baby doll tend to experience a drop in testosterone when they care for the doll together afterward, according to new research published in Human Nature. This hormonal decline occurred for both men and women, though it only emerged across the whole group after they had gained a weekend of hands-on practice with the simulated infant. The findings suggest that experience and pre-existing attitudes toward parenting may help shape how people respond biologically to the demands of joint childcare.
Testosterone is a steroid hormone produced in the bodies of both men and women, though men typically have much higher concentrations. While often associated with aggression or physical competition, testosterone levels actually fluctuate throughout the day in response to different social situations. In evolutionary biology, these shifts are thought to reflect trade-offs that help individuals adapt their behavior to immediate demands.
Higher levels of testosterone tend to support behaviors aimed at finding a mate, competing for status, or defending against threats. Lower levels of the hormone are generally linked to nurturing, bonding, and cooperative caregiving. This biological shift can be seen over long periods: a 2011 longitudinal study found that men’s testosterone tended to fall after they became fathers, especially among those more involved in childcare.
Hormone levels also react within minutes to immediate childcare duties, and the direction of that change depends heavily on the context. For instance, a 2012 experimental study using a programmable baby doll found that men’s testosterone dropped when they were able to successfully soothe the crying doll, but rose when the doll was programmed to be inconsolable. The researchers interpreted this as a sign that feeling able to meet a baby’s needs may favor a drop, while frustration may favor a rise.
Much of the earlier research on hormone changes focused on individuals caring for a real or simulated baby alone. Less is known about how hormones respond when two romantic partners care for an infant together. In a 2025 study of expectant couples, both partners showed an increase in testosterone after trying to soothe an inconsolable baby doll together, which the new study’s authors attribute to frustration with an impossible task.
The new research was led by Rachel E. Brandon, a doctoral student in the Joint Program in Social Work and Psychology at the University of Michigan, alongside senior author Robin S. Edelstein, a professor of psychology at the University of Michigan who directs the Personality, Relationships, and Hormones Lab. Their study was designed to examine how couples without children respond hormonally when they jointly care for a baby doll that can actually be soothed.
By testing couples who had no prior experience raising children, the team could observe how a novel caregiving situation affects testosterone when two partners navigate it side by side. They also wanted to see whether practicing with the doll over a weekend, or holding positive expectations about parenthood beforehand, would make it easier for participants to settle into a nurturing mindset and experience a drop in testosterone.
“People tend to think about testosterone as a ‘male’ hormone associated with aggression and competition; although men certainly have higher levels of testosterone compared to women, this hormone is important for physical and behavioral regulation in both men and women,” Brandon and Edelstein told PsyPost. “Moreover, although both men and women indeed show increases in testosterone in response to competition and in aggressive contexts, they also tend to show decreases in testosterone in more nurturant contexts, including caring for a child. In this study, we wanted to extend this research in two ways: first, by examining how testosterone changed when couples cared for an infant together, and second, by examining how testosterone responses changed as people gained caregiving experience.”
The researchers recruited 30 couples without children, totaling 60 individuals between the ages of 20 and 40 who had been living together for at least a year and planned to have children within the next five years. The sample included 30 male and 30 female participants, with an average age of about 27 and an average relationship length of five and a half years, and about 13 percent of the couples were same-gender. Before visiting the laboratory, all participants completed online surveys measuring how comfortable they felt around babies, how confident they were in their future parenting abilities, and how much personal value and commitment they placed on the role of being a parent.
“One unique feature of our study is that we looked at couples before they became parents,” the researchers noted. “All of the couples were childless but planning to have children within the next five years, and the sample included some same-gender couples. This gave us a window into how people respond to caregiving before they’ve had much real-world practice.”
The study centered on the RealCare Baby, an infant simulator doll used in parenting education that looks, weighs, and sounds like a real newborn. The doll is programmed to cry at set intervals and requires specific types of care, such as feeding with a special bottle, burping, rocking, or changing a diaper. Internal sensors in the doll track whether it is handled gently and whether its needs are met on time, while wristbands worn by the caregivers record how often each partner attends to the baby.
“This allowed us to have some experimental control over the infant’s behavior, and to see how people reacted to the relatively novel experience of caring for an infant,” Brandon and Edelstein explained.
Couples attended a laboratory session on a Friday afternoon or evening, where they received training on how to care for the simulator and gave the doll a name. They then spent 10 minutes alone in a room caring for the doll together while it was programmed to cry regularly and require feeding, burping, diapering, and soothing. To measure short-term changes in testosterone, participants provided saliva samples via oral swabs just before the task and again 10 minutes after the task ended, since steroid hormones in saliva typically take about 20 minutes to reflect a reaction to an event.
After the Friday session, the couples took the infant simulator home to care for it until Monday morning. To mimic different parenting challenges, half of the couples were randomly assigned to a sleep-disruption group in which the doll woke up crying three to six times per night, while the other half received a doll that slept quietly through the night. On Monday, the couples returned to the lab at the same time of day to report their feelings about the weekend and repeat the exact same 10-minute joint caregiving task and saliva collection. Twenty-eight couples completed both lab sessions.
Across the entire group, testosterone levels did not change from before to after the caregiving task during the first laboratory visit on Friday. During that initial session, men showed an average testosterone change of 0.60 percent and women showed an average change of minus 3.29 percent, and the overall average change did not differ from zero. By the second session on Monday, however, participants experienced a notable drop in testosterone after caring for the doll, with levels falling by an average of 9.09 percent in men and 11.53 percent in women. Averaged across everyone, testosterone changed by about minus 1 percent in the first session and about minus 10 percent in the second.
The hormonal declines observed in the second session were consistent across both sexes and did not depend on whether the couple had been assigned to the sleep-disruption group or the uninterrupted sleep group. The findings are in line with earlier research by Edelstein and colleagues covered by PsyPost in 2019, which found that both mothers and fathers experienced short-term drops in testosterone after comforting their own infants during a stressful task, though that earlier work measured actual parents with real babies rather than childless couples using a simulator.
The researchers next tested whether the couples’ experiences over the weekend explained why their testosterone dropped in the Monday session but not the Friday session. Using data from the doll’s internal computer, the team found that couples generally performed well at home, earning an average effectiveness score of about 81 out of 100 and logging an average of 26 caregiving check-ins per person. Even so, neither objective performance scores nor the participants’ self-reported stress or enjoyment over the weekend explained the shift in hormone responses between Friday and Monday. Somewhat unexpectedly, participants whose testosterone rose during the first session tended to describe the weekend of caregiving as less stressful, which the authors suggest may reflect a helpful sense of challenge.
“Most laboratory studies of hormone responses don’t assess hormone changes over repeated sessions, and we were surprised that, on average, we saw larger declines in testosterone in the second compared to the first session,” Brandon and Edelstein said. “This difference might suggest that something about the novelty of the task, especially among people who do not yet have children, contributed to variability in hormone changes in the first session. We were also struck by what didn’t seem to matter: A weekend of disrupted sleep (some couples’ simulators woke them repeatedly overnight) didn’t change their hormone responses, and neither did how well couples cared for the simulator or how much each partner contributed to infant care at home.”
Instead, the change across sessions was linked to the attitudes and comfort levels participants brought into the study before they ever touched the doll. Individuals who initially reported feeling more comfortable around babies, or who placed a high personal value on becoming a parent, tended to show a drop in testosterone during both the Friday and Monday sessions. In contrast, participants who started out feeling uncomfortable around babies or placing less value on parenting showed no hormonal decline on Friday, but experienced a steep drop in testosterone by Monday.
A similar pattern appeared when looking at how confident participants felt about their future parenting skills, though that specific interaction was not statistically significant. The authors suggest that people who already felt at ease with infants may have been able to lean into a nurturing mode more readily, while those who were initially less comfortable may have needed more exposure. By the second session, the less comfortable participants actually showed somewhat larger declines than their more comfortable peers. These moderation results also weakened when the researchers analyzed raw hormone levels rather than percent changes, falling short of statistical significance.
“How people responded the first time depended on how comfortable they felt around babies and how much they valued parenting, but those who started out less comfortable caught up after just one weekend,” the researchers explained. “Our findings also suggest that the ‘new parents’ in our study adapted to caregiving relatively quickly, as indicated by their hormone responses in the second session.”
Brandon and Edelstein also noted that these hormonal shifts should be viewed in the context of normal biological variation and common misconceptions about what lower testosterone means. “People’s testosterone levels differ from one another much more than any one person’s levels change over time,” they said. “So the declines in testosterone that we observe in our studies are relatively small in magnitude and not likely detected by individuals themselves, but they may nevertheless have real-world effects on behavior.”
“In our study, men had higher testosterone levels overall, but men’s and women’s levels changed by similar percentages during caregiving,” the authors added. “Also, ‘low testosterone’ is commonly considered a problem, especially for men. But this study, and research from our lab more generally, suggests that there are many benefits of lower testosterone, particularly in the context of caregiving and parent-child interactions.”
As with all research, there are some caveats to consider when interpreting these results. Caring for a computerized plastic doll, even a lifelike one that demands round-the-clock attention, is not the same as caring for a real human infant with whom parents share a deep biological and emotional bond. Because of this, the hormonal shifts seen during a weekend simulation may not perfectly mirror how people’s bodies react when they transition into actual parenthood.
The study also relied on a relatively small sample of 30 couples who were mostly white, college-educated, and middle-class, which limits how broadly the findings can be applied to the general public. The analyses were exploratory and not preregistered, and the researchers did not calculate in advance how large a sample they would need to detect effects. In addition, about half of the female participants were using hormonal contraceptives, and the sample was too small to test whether birth control medications altered how their testosterone responded to the doll.
“Our sample was relatively small, so it will be important to replicate our findings in other, larger samples,” Brandon and Edelstein said. “Of course, because we used a simulated infant in this study, not a real infant, the extent to which our findings are applicable to real infants remains to be tested in future studies.”
Another point to keep in mind is that every couple took the baby doll home for the weekend between the two laboratory sessions. Without a comparison group of couples who simply did the two lab tasks without the weekend practice, it is impossible to know for sure whether the Monday hormone drop was caused by the weekend of caregiving or simply by the laboratory room and task feeling less novel the second time around. In romantic couples, novel joint activities can sometimes spark excitement or attraction that keeps testosterone elevated, which may have masked any nurturing-related hormone drops during the Friday visit.
Future studies could help separate the effects of hands-on practice from simple familiarity by comparing couples who take the simulator home against couples who only interact with it briefly in the lab. Researchers might also directly measure how capable and effective partners feel in the moment as they work together to soothe a baby, as well as test larger and more diverse groups of couples. Exploring these details will help scientists better understand how romantic partners adjust biologically and emotionally as they learn to share the workload of raising a child.
“We’re also interested in the extent to which couple members’ hormones may be correlated, or synchronized, during different kinds of interactions,” Brandon and Edelstein said. “Are partners’ testosterone levels more likely to rise and fall together during caregiving interactions, for instance, compared to laboratory stressors? How might other hormones, such as cortisol, change during caregiving, and are couple members’ cortisol responses synchronized?” Cortisol is a hormone involved in the body’s stress response.
The study, “Testosterone Changes in Couples in Response to a Caregiving Task with an Infant Simulator,” was authored by Rachel E. Brandon, Annika From, Miranda Reynaga, Helen Devine, Amie M. Gordon, and Robin S. Edelstein.