Children consider unique similarities as more meaningful cues to compatibility in social partnerships

Given finite resources in developing and maintaining social relationships, humans have likely evolved to prioritize investing in individuals with high association value, or those who provide the greatest net benefits in mutual interaction. While it is well established that similarity guides affiliative judgments, it remains unclear which types of similarity provide a meaningful foundation for effective social partnerships and thus signal higher association value. The current study aimed to investigate (1) how children weigh the importance of shared social category and shared preferences as cues to potential social partnerships, and (2) whether the weight that children place on shared preferences depends on their rarity. We assessed third-party friendship inferences in 106 children (ages 4 to 12) in Japan by having them predict friendships between characters based on their gender and preferences. Children privileged shared preferences over shared gender, predicting that a character would be friends with an other-gender character who shared their preference than a same-gender character who did not. Further, this tendency to prioritize shared preferences was slightly stronger when the preferences were rare rather than common. When multiple types of similarity cues are available, it may be adaptive to select social partners based on unique similarities which signal that the individual offers irreplaceable benefits that are not easily supplied by others.