Physical Strength Linked With Sexual Success in Men and Women

A study found that both men and women with greater upper body strength reported having more sexual partners, defying traditional evolutionary theories.

While men’s strength has been linked to mate competition and resource provision, the reasons behind women’s strength and mating success remain unclear.

Strength and Sexual Behavior: Surprising Links

A recent study from Washington State University explored the evolutionary connection between physical strength and sexual behavior, and it revealed a surprising finding—this link applies to both men and women. The research found that individuals, regardless of gender, who had greater upper body strength tended to report a higher number of lifetime sexual partners compared to their peers.

Published in the journal Evolution and Human Behavior, the study aimed to test theories about human sexual dimorphism—the physical differences between men and women—by examining whether greater upper body strength provided a reproductive advantage in early human history.

Strength and Long-Term Relationships

Interestingly, the study also suggested a potential reason for men’s historically greater upper body strength. It found that men with higher strength levels were more likely to be in long-term relationships, indicating that strength may have played a role not only in attracting multiple partners but also in forming lasting bonds.

“People have assumptions about men’s sexual behavior and how that’s related to evolution. Besides acquiring more sexual partners, establishing long-term relationships was likely also important for men in evolutionary history,” said lead author Caroline Smith, a recent WSU PhD graduate in anthropology.

For this study, Smith and her advising professor, WSU evolutionary anthropologist Ed Hagen, analyzed data on 4,316 U.S. adults from 2013–2014 from the National Health and Nutrition Examination Survey conducted by the Centers for Disease Control and Prevention. They primarily used grip strength, a common measure to approximate upper body strength, and compared it to participants’ survey responses about their sexual behavior.

The findings present a mixed picture, the authors said.

The Sexual Selection Hypothesis

There are several hypotheses around why men have greater upper body strength. One popular theory, known as the sexual selection hypothesis, is based on competition: that like other primates, human males competed against each other for access to mates so needed to be physically formidable to pass their genes on. This theory predicts little relationship between women’s strength and their mating success.

“Regardless of whether they’re males or females, stronger individuals have more lifetime sexual partners. That was a surprising finding and somewhat contrary to the sexual selection hypothesis.”

Ed Hagen, evolutionary anthropologist, Washington State University

“Men are stronger than women, on average, and men report more lifetime partners than women, but men and women are on the same regression line,” said Hagen. “Regardless of whether they’re males or females, stronger individuals have more lifetime sexual partners. That was a surprising finding and somewhat contrary to the sexual selection hypothesis.”

Provisioning Theory and Partnering

On the other hand, this study’s finding about long-term partners seems to support another theory based on “provisioning.” Since human babies require a lot of care and resources, particularly from women during pregnancy and lactation, men were more desirable as partners when they could provide meat through hunting, which for hundreds of thousands of years before the modern era required upper body strength. The stronger human males, who also stuck around and helped provide more food resources to those children as they grew, also would better ensure their survival.

Women’s Strength and Mating Success

While there are theories for men’s strength in relation to reproductive success, there are not so many for women’s strength, in part because women are not often included in these types of studies.

There was not an obvious explanation in this study’s data why women with greater upper body strength also had greater number of lifetime partners. The researchers controlled for many variables, including general health and testosterone levels, but the connection still held. They did cite a few potential theories, including that it is due to “assortative mating,” meaning physically stronger people tend to partner with each other more frequently. It could also be that women who are physically stronger require less male investment or feel like they can take more risks.

Ultimately, more studies involving women would be needed to uncover more evidence for the reasons behind this connection as well as a better understanding of human evolution in general.

“I believe it’s important to continually test our theories, especially by expanding our research questions to include women,” said Smith.

Reference: “Strength, mating success, and immune and nutritional costs in a population sample of US women and men: A registered report” by Caroline B. Smith and Edward H. Hagen, 6 January 2025, Evolution and Human Behavior.
DOI: 10.1016/j.evolhumbehav.2024.106647

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