Sibling interference in mother-offspring interactions reveals jealous reactions in wild baboons

Whether non-human animals can experience complex emotions like jealousy remains debated. In humans, jealousy is particularly salient in sibships, where children often disrupt affiliative parent-sibling interactions. Jealousy could similarly mediate competitive interactions among siblings in animals. Here, we examine the context, targets and function of sibling interference in mother-offspring grooming interactions in wild chacma baboons. We test the jealousy hypothesis proposing that juveniles interfere to disrupt parent-sibling affiliation without immediate reward, alongside two alternatives stating that interference instead aims at interacting with the mother or sibling. Our results support the jealousy hypothesis, with patterns strikingly echoing observations on children. First, juveniles approach their mother more often when she is grooming a sibling than when she is socially available. Second, they preferentially target same-sex and younger siblings, as well as 'maternal favourites' that receive a disproportionate share of maternal grooming. Third, interference is more successful at disrupting mother-sibling grooming than at obtaining attention from either the mother or the sibling. This study introduces a novel framework to study the expression of jealousy and the emotional mechanisms underpinning family conflicts in animals, thereby opening perspectives in the growing field of the ecology of emotions.