Purpose <p>This study experimentally tested the impact of perceived physical resemblance on ascriptions of close relationships between individuals. Following kin selection theory, if physical resemblance is a proxy for genetic relatedness, it is adaptive to act altruistically toward similar-looking individuals who may share genes in common, yet select dissimilar-appearing romantic partners to avoid mating that may result in inbreeding depression or lack of offspring diversity.</p> Methods <p>Participants were shown sets of paired facial photos of two persons varying in physical resemblance to one another, who were labeled as being either friends, siblings, or romantic partners. Raters evaluated the closeness of each pair’s relationship based on their pictures. Another set of raters was shown the same pairs of photos without relationship labels and was asked to evaluate how likely they thought the pairs were siblings, friends, or romantic partners, respectively.</p> Results <p>Across all conditions, pairs exhibiting greater perceived physical resemblance were rated as having closer/higher-quality relationships and were more likely thought to be siblings or friends, but were less likely seen as romantic partners. Similar patterns were found when participants (<i>n</i> = 526) were asked about their own personal relationships; generally, ratings of both perceived physical and behavioral similarity were positively associated with perceived relationship closeness across all relationship types, even when controlling for factors such as relationship length and residence distance.</p> Conclusion <p>In line with kin selection theory, participants ascribed closer relationships to those who appeared more genetically related but were less likely to identify similar-looking pairs as being romantic partners.</p>