New research suggests that a potential partner’s willingness to protect you from physical danger is a primary driver of attraction, often outweighing their actual physical strength. The findings indicate that these preferences likely stem from evolutionary adaptations to dangerous ancestral environments, persisting even in modern, relatively safe societies. This study was published in the journal Evolution and Human Behavior.
Throughout human evolutionary history, physical violence from other humans posed a significant and recurrent threat to survival. In these ancestral settings, individuals did not have access to modern institutions like police forces or judicial systems. Instead, they relied heavily on social alliances, including romantic partners and friends, for defense against aggression. Consequently, evolutionary psychology posits that humans may have evolved specific preferences for partners who demonstrate both the capacity and the motivation to provide physical protection.
Previous scientific inquiries into partner choice have frequently focused on physical strength or formidability. These studies often operated under the assumption that strength serves as a direct cue for protective capability. But physical strength and the willingness to use it are distinct traits. A physically powerful individual might not be inclined to intervene in a dangerous situation, whereas a less formidable individual might be ready to defend an ally regardless of the personal risk.
Past investigations rarely separated these two factors, making it difficult to determine whether people value the ability to fight or the commitment to do so. The authors of the current study aimed to disentangle the capacity for violence from the motivation to employ it in defense of a partner. They sought to understand if the mere willingness to face a threat is sufficient to increase a person’s desirability as a friend or mate.
“Nowadays, many of us live in societies where violence is exceedingly rare, and protection from violence is considered the responsibility of police and courts. As such, you wouldn’t really predict that people should care if their romantic partner or friends are or are not willing to step up to protect them during an altercation,” said study author Michael Barlev, a research assistant professor at Arizona State University.
“However, for almost the entire history of our species, for hundreds of thousands of years, we lived in a social world scarred by violence, multiple orders of magnitude higher than it is today, and where protection was the responsibility of romantic partners, family, friends, and coalitional allies. Our psychology, including what we look for in romantic partners and friends, evolved to survive in such a world.”
To investigate this, the research team conducted a series of seven experiments involving a total of 4,508 adults from the United States. Participants were recruited through Amazon Mechanical Turk. The study utilized a vignette-based methodology where participants read detailed scenarios asking them to imagine they were with a partner, either a date or a friend.
In the primary scenario used across the experiments, the participant and their partner are described leaving a restaurant. They are then approached by an intoxicated aggressor who attempts to strike the participant. The researchers systematically manipulated the partner’s reaction to this immediate threat.
In the “willing” condition, the partner notices the danger and physically intervenes to shield the participant. In the “unwilling” condition, the partner sees the threat but steps away, leaving the participant exposed. A control condition was also included where the partner simply does not see the threat in time to react. In addition to these behavioral variations, the researchers modified the descriptions of the partner’s physical strength, labeling them as weaker than average, average, or stronger than average.
The data revealed that discovering a person is willing to protect significantly increased their attractiveness rating as a romantic partner or friend. This effect appeared consistent regardless of the partner’s described physical strength. The findings suggest that the intent to defend an ally is a highly valued trait in itself. In contrast, partners who stepped away from the threat saw a sharp decline in their desirability ratings compared to the control condition.
“We present evidence that our partner choice preferences—what we look for in romantic partners and friends—are adapted to ancestral environments,” Barlev told PsyPost. “I think that is a very important—and generally unappreciated—fact about partner choice preferences, and psychology more generally.”
The researchers also uncovered distinct patterns based on gender, particularly regarding the penalty for unwillingness. When women evaluated male dates, a refusal to protect acted as a severe penalty to attractiveness. The ratings for unwilling men dropped precipitously, suggesting that for women seeking male partners, a lack of protective instinct is effectively a dealbreaker.
Men also valued willingness in female partners, but they were more lenient toward unwillingness. When men evaluated female dates who stepped away from the threat, the decline in attractiveness was less severe than what women reported for unwilling men. This asymmetry aligns with evolutionary theories regarding sexual dimorphism and the historical division of risk in physical conflicts.
“We found that willingness was hugely important, for raters of both sexes, and when rating both male and female friends and dates,” Barlev said. “In particular, when women rated male dates, willingness to protect was very attractive, whereas failure to do so—stepping away—was a deal-breaker (the attractive of unwilling to protect men plummeted compared to when no information about willingness or unwillingness to protect was given).”
The researchers also explored the role of physical strength. While women did express a preference for stronger men, a mediation analysis clarified the underlying psychological mechanism. The analysis suggested that women tended to infer that stronger men would be more willing to protect them.
Once this inference of willingness was statistically controlled, physical strength itself had a much smaller independent effect on attraction. This indicates that strength is attractive largely because it signals a higher probability of protective behavior.
Subsequent experiments tested the limits of this preference by manipulating the outcome of the confrontation. The researchers introduced scenarios where the partner attempts to intervene but is overpowered and pushed to the ground. Surprisingly, the data showed that a partner who tries to help but fails is still viewed as highly attractive. The attempt itself appeared to be the primary driver of the positive rating, rather than the successful neutralization of the threat.
A final experiment examined the most extreme scenario where the partner fails to stop the attack and the participant is physically harmed. In this condition, the aggressor strikes the participant after the partner’s failed intervention.
Even in cases where the participant suffered physical harm because the partner failed, the partner remained significantly more attractive than one who was unwilling to act. This suggests that the signal of commitment inherent in the act of defense carries more weight in partner evaluation than the immediate physical outcome.
The study also compared preferences for friends versus romantic partners. While willingness to protect was valued in both categories, the standards for friends were generally more relaxed. The penalty for being unwilling to protect was nearly three times more severe for romantic partners than for friends. This difference implies that while protection is a valued attribute in all close alliances, it is considered a more critical requirement for long-term mates.
“Strength—or more generally, ability to protect—mattered only little, much less than we thought it would,” Barlev explained. “In our earlier experiments, women showed a weak preference for strength in male dates, but most of this had to do with the underlying inference that stronger men would be more willing—rather than more able—to protect them. In fact, in our later experiments, women found dates attractive even if they tried to protect but failed, and such dates were not less attractive than dated who tried to protect and succeeded.”
“That’s surprising, because whether you protect someone is a function of both your willingness and ability to do so. But here’s one way to think about this: If the aggressor is a rational decision-maker, his decision of whether to fight or retreat depends not only on his strength relative to yours but also on how much each side is willing to risk. So, he should not attack you even if you are weaker if you show that you are willing to risk a lot. Meaning, potentially even more important than how strong you are is your readiness to step up and fight when it’s needed.”
As with all research, there are some limitations to keep in mind. The study relied on hypothetical vignettes rather than real-world behavioral observations. While imagined scenarios allow for precise control over variables, they may not perfectly capture how individuals react during actual violent encounters. Participants might overestimate or underestimate their emotional reactions to such visceral events when reading about them on a screen.
Additionally, the sample consisted entirely of participants from the United States. This geographic focus means the results reflect preferences in a modern Western society where rates of interpersonal violence are historically low compared to ancestral environments. It remains to be seen whether these preferences would differ in cultures with higher rates of daily violence. Preferences for physical strength might be more pronounced in environments where physical safety is less assured by external institutions.
“One big next step is to ask how preferences for physical strength and willingness to protect vary across societies,” Barlev told PsyPost. “Both preferences are likely tuned to some extent to the social and physical environment in which people live, such as how dangerous it is. Strength in particular can be an asset or a liability—strong individuals, especially men, would be better able to protect themselves and others from violence, but such men might also be more violent toward their romantic partners and friends.”
“Because most of our American participants live in relatively safe environments, their weaker preference for strength may partially reflect this down-regulation. If that’s right, we’d predict that people in more dangerous environments will value both strength and willingness to protect somewhat more.”
The study, “Willingness to protect from violence, independent of strength, guides partner choice,” was authored by Michael Barlev, Sakura Arai, John Tooby, and Leda Cosmides.
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