A new study has shed light on relationships between hormones, fertility, and competitive behavior in women. Researchers discovered that while natural fluctuations in fertility across the menstrual cycle do not appear to influence a woman’s competitive motivation or actions, the use of hormonal contraceptives is associated with a reduced interest in competition. This finding, published in Evolution and Human Behavior, raises important questions about the wider effects of hormonal birth control beyond pregnancy prevention.
Scientists have long been interested in how hormones shape human behavior, particularly in areas related to reproduction and survival. Competition, in its broadest sense, is a fundamental aspect of life, occurring whenever individuals vie for limited resources. From an evolutionary perspective, humans have developed biological and behavioral systems that help them succeed in competitive environments, ultimately increasing their chances of survival and passing on their genes.
Previous research has explored whether the natural hormone changes that occur throughout a woman’s menstrual cycle are linked to shifts in competitive drive. However, the results of these studies have been inconsistent, leaving scientists unsure about the true relationship between ovarian hormones and a woman’s desire to compete and engage in competitive actions. This lack of clarity prompted researchers to conduct a new, more in-depth investigation into this area.
“I’ve always been interested in understanding how signals from the body can shape psychological experiences and behavior,” said study author Lindsie Catherine Arthur, a PhD candidate at The University of Melbourne.
“Competitive motivation is a fundamental aspect of many areas of life, from sports to careers, yet we often overlook the role that hormonal fluctuations might play in these dynamics. Because the menstrual cycle and hormonal contraceptives appear to influence a wide range of psychological processes (such as mood and sexual desire), I wanted to explore how they might impact competitiveness—something that is critical for success in various domains.”
The researchers conducted a detailed study using an online diary method. They recruited 302 women, with an average age of 22, from both a university student pool and the wider community. Participants had to be fluent in English, have regular menstrual cycles, and be confident in their knowledge of their cycle length. Women were excluded if they had certain medical conditions affecting fertility or hormone levels, or if they had recently used emergency contraception, were breastfeeding, or pregnant.
Of the participants, 231 were naturally cycling, meaning they were not using hormonal birth control, while 71 were using hormonal contraceptives, such as birth control pills or hormonal intrauterine devices. The group of hormonal contraceptive users included women using various types, including different generations of oral pills and hormonal intrauterine devices. The demographic makeup of the participants was diverse in terms of sexuality, relationship status, and ethnicity, reflecting a broad range of backgrounds.
The study was designed as a longitudinal diary study, meaning that the same women were tracked over time, providing daily reports. Participants completed a baseline survey to gather information about their demographics and menstrual cycles. Then, for at least 28 days, they filled out a daily survey at 5 pm each day. These surveys asked about their current menstrual cycle status, as well as their feelings and behaviors related to competition, and other psychological factors.
After the initial 28-day period, women could choose to continue participating for another 28 days. To encourage participation, some women received course credit, while others volunteered in exchange for a personalized report about their menstrual cycle patterns. Ten days after their final survey, participants were asked to complete a follow-up survey to record the start date of their next menstrual period.
To measure competitive motivation, the researchers used a well-established questionnaire that assesses different aspects of competitiveness. They focused on two specific aspects: achievement-oriented competitiveness, which reflects a desire to do well and excel, and lack of interest in competition, which indicates a general disinterest in competitive situations. Participants rated their agreement with statements like “Competitive situations allowed me to bring out the best of myself” (for achievement-oriented competitiveness) and “I didn’t care about being the best” (for lack of interest in competition) each day on a five-point scale.
To capture competitive behavior, the researchers developed a new set of questions asking women to report daily on whether they had engaged in certain behaviors that can be related to competition for mates and status. These behaviors included gossiping about someone, spending time on appearance enhancement (like hair, makeup, and clothes), taking selfies, giving advice to others, comparing themselves to others, and looking for negative qualities in others. Participants rated how much they had engaged in each of these behaviors each day on a five-point scale. The researchers found that these six behaviors tended to occur together, suggesting they could be grouped into a single measure of competitive behavior.
Finally, to understand the role of fertility, the researchers estimated each woman’s daily probability of being fertile based on her reported menstrual cycle dates. They used a method called “backward counting,” which calculates fertility probability based on the estimated or reported start date of menstruation. This allowed them to track changes in fertility probability across the menstrual cycle for both naturally cycling women and those using hormonal contraceptives. Importantly, fertility probability was estimated for all participants, even those on hormonal birth control, to allow for a direct comparison between the groups and to see if any fertility-related patterns were unique to naturally cycling women.
Contrary to what they initially expected, the researchers found no link between a woman’s daily fertility probability and her self-reported competitive motivation or competitive behaviors. This means that for naturally cycling women, their reported desire to achieve or their engagement in competitive actions did not change depending on where they were in their menstrual cycle and how likely they were to be fertile.
However, the study did confirm previous research showing a difference between women who use hormonal contraceptives and those who do not. The researchers found that women using hormonal contraceptives consistently reported a greater lack of interest in competition compared to naturally cycling women. This suggests that hormonal birth control might be associated with a general dampening of competitive drive. This effect was not influenced by whether a woman was in a relationship or not.
Interestingly, when relationship status was considered in the analysis, hormonal contraceptive users also reported engaging in slightly more competitive behaviors overall, although this finding was less robust and requires further investigation. However, the main finding of reduced interest in competition among hormonal contraceptive users remained consistent.
“The main takeaway is that hormones are an important but often invisible factor in motivation and behavior,” Arthur told PsyPost. “We found no evidence that competitive motivation fluctuates across the menstrual cycle, challenging the idea that fertility boosts a woman’s competitiveness. However, we did observe that women using hormonal contraceptives reported generally lower interest in competition compared to non-users.”
“This raises important questions about how hormonal contraceptives influence motivation and behavior beyond their primary function of preventing pregnancy. While more research is needed, these findings highlight the need for research to evaluate the broader psychological and social effects of hormonal contraceptive use.”
The researchers acknowledge some limitations to their study. Diary studies, while useful for tracking changes over time, may not fully capture the complex social context in which competitive behaviors occur. Additionally, the study relied on women’s self-reports.
“While diary studies provide rich longitudinal data, self-reporting can be influenced by factors like social desirability bias or individual differences in interpreting survey questions,” Arthur said. “Additionally, while we accounted for cycle phase using a well-established fertility probability estimation method, we did not measure hormone levels directly.”
Despite these limitations, the study provides valuable insights into the relationship between hormones, fertility, and competition. The lack of connection between fertility probability and competitive motivation in naturally cycling women challenges some existing theories about hormonal influences on female competition. The consistent finding that hormonal contraceptive use is linked to a reduced interest in competition highlights the potential for these medications to have broader psychological effects that warrant further investigation. Future research should explore the underlying mechanisms behind this effect, perhaps by examining how hormonal contraceptives affect specific brain processes related to motivation and reward.
The study, “Hormonal contraceptive use, not menstrual cycle phase, is associated with reduced interest in competition,” was authored by Lindsie Catherine Arthur, Brock Bastian, and Khandis Rose Blake.
