Distribution of facial resemblance in romantic couples suggests both positive and negative assortative processes influence human mate choice

Iris J Holzleitner, Kieran J O’Shea, Vanessa Fasolt, Anthony J Lee, Benedict C Jones & Lisa M DeBruine

Abstract

Previous research suggests that humans show positive assortative mating, i.e. tend to pair up with partners that are similar to themselves in a range of traits, including facial appearance. Facial appearance can function as a cue to genetic similarity and plays a critical role in human mate choice. Evidence for positive assortative mating for facial appearance has largely come from studies showing people can match pictures of couples’ faces at levels greater than chance and that facial photographs of couples are rated to look more similar than those of noncouples. However, interpreting results from matching studies as evidence of positive assortative mating for facial appearance is problematic, since this measure of perceived compatibility does not necessarily reflect actual physical similarity, and may be orthogonal to, or even negatively correlated with, physical similarity. Even if participants are asked to rate facial similarity directly, it remains unclear which, if any, face shape cues contribute to an increased perception of similarity in romantic couples. Here we use a shape-based assessment of facial similarity to show that the median similarity of long-term couples’ face shapes is only slightly greater than that of an age-matched control sample. Moreover, this was driven by the most similar 40% of couples, while the most dissimilar 20% of couples actually showed disassortative mating for face shape when compared to the control sample. These data show that a simple measure of central tendency obscures variability in the extent to which couples display assortative or disassortative mating for face shape. By contrast, a more fine-grained analysis that considers the distribution of variation across couples in the extent to which they resemble each other suggests that both positive and negative assortative processes influence human mate choice

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"The extent to which romantic couples physically resemble each other is a long-standing question with implications for influential theories of mate choice, such as optimal outbreeding theory. Optimal outbreeding theory acknowledges that mating with closely-related individuals can have a large negative effect on reproductive fitness (i.e., results in less viable offspring), but emphasizes that excessive outbreeding (mating with highly genetically dissimilar individuals), too, can have a negative effect on reproductive fitness. Consequently, while folk psychology theories predict that romantic couples will physically resemble each other, optimal outbreeding theory predicts that both assortative and disassortative processes may influence human mate choice."