Objectively Measured Facial Similarity Predicts Ratings of Facial Attractiveness in a Large Speed-Dating Dataset

– By Amy Zhao and Brendan Zietsch

Ariana Grande and Ethan Slater have been making headlines due to their alleged affair, which occurred while both parties were married to their respective partners. Another aspect of their relationship that hasn’t gone unnoticed is Ethan Slater’s striking resemblance to Ariana Grande’s brother, Frankie.

This is just one example of a couple who look like siblings. Many of you may even have your own stories of having mistaken a couple for being siblings, a phenomenon so common that it has led to the creation of a popular Instagram account called Siblings or Dating.

Despite all this anecdotal evidence, there has been mixed empirical evidence as to whether couples actually share facial similarities. But even if we assume that couples do have similar faces, it’s unclear why someone would even date another person who looks similar to themselves in the first instance.

Some researchers have proposed that couples might look similar because couples share the same lifestyles, diet, exercise, stressors, etc. and so, couples’ faces become more and more similar over time. However, there is mixed evidence to support this hypothesis.

Instead of couples’ faces converging over time, an alternative theory is that individuals prefer facially similar partners to begin with; that is, individuals find similar faces attractive. However, there is mixed evidence for this association too. The studies from which these mixed findings have been derived are flawed in several ways. Firstly, these studies have exclusively measured facial attractiveness through participants’ ratings of 2D images. These images consist of photographs of real-life participants, or they are computer generated/digitally morphed faces. There are several implications of using images to obtain attractiveness ratings. Firstly, humans have relied (until most recently) on face-to-face interactions to interact and form judgments about another person, especially another potential mate. And secondly, morphed faces can lack realistic features such as facial hair, skin texture, or head hair. Therefore it is unclear whether past findings can validly reflect real-life behaviours and preferences. In addition, facial traits (such as similarity, averageness, and masculinity) are often subjectively rated by participants. These facial trait ratings may be conflated with ratings of facial attractiveness and can be subject to other biases (e.g. the halo effect).

We conducted a large speed-dating experiment with 682 participants and there were 2285 speed-dating interactions. Participants speed-dated members of the opposite sex for 3 minutes at a time. After these interactions, participants rated their speed-dating partners on facial attractiveness, and kindness and understanding. We landmarked the facial photographs of all participants and calculated objective, data-driven scores for facial averageness, facial similarity, and facial masculinity to address the limitations of subjective ratings of such facial traits.

We found that participants rated partners who had geometrically similar faces to their own as more attractive, showing that individuals do in fact have a preference for facially similar opposite-sex individuals.

The question still remains, why do people even find facially similar people more attractive in the first case?

We found that people with similar faces also rated speed-dating partners as more kind and understanding, even when controlling for the ethnicity of the participant and partner. Our findings are in line with an alternative explanation where a preference for similarity is not driven by the attractiveness of similar faces per se, but that similar faces may signal kinship. While cues of kinship can decrease sexual desirability due to the costs of inbreeding, the same cues can increase positive social behaviour by promoting increased chances of survival via altruistic and cooperative behaviour from others (inclusive fitness benefits). There is also evidence that positive assortative mating (mating with someone who is similar) can result in net positive reproductive benefits, as a small degree of genetic relatedness is associated with higher fertility.

Sure, we have shown that individuals do prefer similar faces, but does this preference extend to real-life mate choice?

We’re not sure. Actual mate choice involves the mutual desire to form a romantic partnership, but these decisions are constrained by the mating market. For instance, individuals with high mate value are unlikely to pair with low mate value individuals. Given that not everyone can satisfy their preferences, individuals must make compromises. In addition, the effects we found in our study are small, and therefore these preferences may not carry through to realised mate choice. It would be a worthwhile future endeavour to investigate how the objective facial characteristics measured in our study relate to real couples.

Read the original article: Zhao, A.A.Z., Harrison, K., Holland, A., Wainwright, H.M., Cecatto, J.-M., Sidari, M.J., Lee, A.J., & Zietsch, B.P. (2023). Objectively measured facial traits predict in-person evaluations of facial attractiveness and prosociality in speed-dating partners. Evolution & Human Behavior, 44(4), 315-323.