Fairness informs social decision making in infancy.

The ability to reason about fairness plays a defining role in the development of morality. Thus, researchers have long been interested in understanding when and how a sensitivity to fairness first develops. Here, we examined infants' ability to use fairness information in selecting social partners. Using a novel experimental paradigm that combined pre-recorded stimuli with an active behavioral measure, we tested whether infants preferred to socially engage with an individual they had previously seen behave fairly or unfairly. After viewing an individual distribute goods to third parties either equally (i.e., 3:3 distribution) or unequally (i.e., 5:1 distribution), both 13- and 17-month-old infants selectively chose to engage in a social interaction with (i.e., take a toy from) an individual who distributed resources equally. The use of a novel paradigm to assess infants' fairness preferences demonstrates that infants' previously established fairness preferences extend across different, more demanding paradigms, and may therefore be more enduring in nature. Together, these findings provide new insights into the nature of infants' fairness representations, and fill in key gaps in the developmental timeline of infants' ability to use fairness information in their consideration of potential social partners. In sum, these findings build on previous research by demonstrating that infants not only hold an expectation that resources should be distributed fairly, they also preferentially interact with those who have previously done so. The early-emerging ability to both reason about and use fairness information may play an influential role in the development of complex prosocial behaviors related to morality more broadly.