Sensitivity to immature skill deficits. Food sharing experiments in squirrel monkeys (Saimiri boliviensis) and common marmosets (Callithrix jacchus).

Sharing food with immature individuals is costly and should therefore only occur when the benefits outweigh the costs. Accordingly, sharing typically decreases when immature individuals get older and become more proficient independent foragers. Providers would gain more if they could adjust food sharing not only to immature age but also to their skill level. Such sensitivity to others' skill deficits is expected to be rare, but may be found in species with high prosociality and other-regarding preferences, such as cooperative breeders. Here, we compared the food-sharing patterns of cooperatively breeding common marmosets (Callithrix jacchus) and closely related but independently breeding squirrel monkeys (Saimiri boliviensis) under two conditions. In the baseline condition, food was easily accessible whereas in the experimental condition, individuals had to solve a puzzle to access the food. We found that the cooperatively breeding marmosets, but not the independently breeding squirrel monkeys, shared more when immatures lacked the skill to obtain the food from the apparatuses. Skill sensitivity might be associated with the presence of other-regarding preferences and a strong proclivity to proactively share food during baseline conditions. This proclivity has evolved in marmosets, but not squirrel monkeys, in the context of cooperative breeding and may facilitate the emergence of skill recognition, information donation, and teaching. (PsycInfo Database Record (c) 2025 APA, all rights reserved).