Humans are wired to quickly spot subtle differences in strength and beauty, new study suggests

A new study published in Evolution and Human Behavior has found that people are surprisingly sensitive to small differences in how attractive or physically formidable others appear. Participants were quicker and more likely to choose the person rated as more attractive or strong when the difference between two individuals was more pronounced—but even slight differences influenced their choices and reaction times. These findings suggest that our minds are finely tuned to pick up on traits that may have influenced social and reproductive outcomes throughout human history.

Researchers at Charles University conducted the study to better understand how people judge physical characteristics that matter in social interactions, such as attractiveness and strength. While past studies have shown that people can identify traits like dominance or beauty from facial features alone, most of that research presented images one at a time or compared extremely different images—such as digitally altered faces made to look more masculine or feminine. The problem is that real-life social decisions rarely involve such dramatic contrasts. In everyday life, people usually compare individuals who fall along a continuum of similarity.

The study aimed to test whether people are equally good at detecting smaller, more natural differences between individuals. The researchers wanted to find out whether participants’ ability to make judgments improved in a gradual, step-by-step way as differences between people increased—or whether there was a threshold below which people could no longer reliably tell who was more attractive or formidable. If such a threshold existed, it would suggest that when two people look very similar, observers might have to guess. If, on the other hand, judgments improved steadily with increasing difference, this would indicate that human perception is finely attuned to even subtle variations.

To investigate this, the researchers conducted two related studies. One was an online experiment with 446 participants, and the other was a controlled, in-person study with 56 participants. All participants were between 18 and 40 years old and were recruited via social media.

Participants were shown 30 pairs of male faces and 30 pairs of male bodies. These images were photographs of real individuals—mixed martial arts fighters—who varied naturally in appearance. None of the images were digitally altered, and facial and body photographs were presented separately. Participants were randomly assigned to evaluate either attractiveness or formidability, and they were asked to choose the more attractive or formidable person in each pair. The images were presented side by side, and participants were encouraged to respond quickly and go with their gut.

In the online version, people used their own devices to complete the survey, while the in-person version took place in a lab with standardized lighting and equipment. In both studies, the researchers measured which image was selected and how long it took participants to make a decision.

The researchers then compared the participants’ choices to previously collected ratings of each image’s attractiveness and formidability. This allowed them to quantify the difference between each pair of images and examine how that difference affected participants’ decisions.

The researchers found that participants were more likely to choose the person with the higher attractiveness or formidability rating, and they did so faster when the difference between the two individuals was larger. There was no evidence of a threshold where people began guessing randomly.

Even when the differences were small, people were still more likely to choose the image rated slightly higher. For example, a one-point difference on a seven-point scale led to a strong increase in the probability of choosing the higher-rated image—above 80 percent in many cases. A two-point difference pushed that likelihood close to 100 percent.

These effects were observed for both facial and body images. However, participants’ choices were slightly more predictable when they judged body images, especially for formidability. The same patterns held in the smaller in-person study, suggesting the results were reliable across different settings.

In addition to rating differences, the researchers also explored whether other characteristics—like the age, height, and weight of the individuals in the images—played a role in selection. While these features did influence decisions to some extent, especially in judgments of formidability, their effects were much weaker than the main rating differences. For example, heavier and taller individuals were more likely to be judged as more formidable when shown in body images. Younger individuals tended to be judged as more attractive, but these effects were inconsistent and often disappeared when the researchers accounted for the attractiveness ratings.

The speed of participants’ decisions also followed a predictable pattern. When the difference between the two images was greater, people made their choices faster. On average, participants took between two and six seconds to make a decision. Judging body images tended to take slightly longer than judging faces. This might reflect the complexity or novelty of evaluating full-body appearance compared to facial features, which humans may process more automatically.

Interestingly, the researchers found individual differences in how people made their choices. Some participants relied more on height when judging formidability, while others gave more weight to body size. However, participants tended to be consistent in their own preferences across different comparisons.

There were no strong differences between men and women in the likelihood of selecting more attractive or formidable individuals. However, some sex differences did emerge in decision speed. In the in-person study, women tended to make decisions more quickly than men, while in the online study, women took slightly longer. The researchers suggest this could be due to differences in how the tasks were performed—such as pressing a spacebar in the lab versus clicking on a screen at home—rather than underlying differences in perceptual ability.

While the results provide strong evidence that people can discriminate even subtle differences in attractiveness and strength, the study does have some limitations. One is that all the images used were of men. This means the findings may reflect processes related to intrasexual competition among men and mate selection by women, but they don’t necessarily reveal how people evaluate female faces or bodies. Future research could explore whether similar patterns hold for female targets or for same-sex judgments among women.

Another limitation is the artificial nature of the forced-choice design. In real life, people are not always required to make a choice between two options. They might consider additional factors, take more time, or decide that neither option stands out. Adding a “no difference” option in future studies could help capture more realistic decision-making processes.

The study, “Even small differences in attractiveness and formidability affect the probability and speed of selection: An online study and an offline replication,” was authored by Vít Třebický, Petr Tureček, Jitka Třebická Fialová, Žaneta Pátková, Dominika Grygarová, and Jan Havlíček.