Who helps Tsimane youth?

We examine various forms of helping behaviour among Tsimane Amerindians of Bolivia, focusing on the provision of shelter, childcare, food, sickcare, cultural influence and traditional story knowledge. Kin selection theory traditionally explains nepotistic nurturing of youth by closely related kin. However, less attention has been given to understanding the help provided by individuals without close genetic relatedness. To explain who provides various forms of help, we evaluate support for several predictions derived from kin selection theory. Our results show that helpers who are most often closely related and from an older generation tend to provide more costly forms of help to youth at early ages. In contrast, alloparents who are not blood related tend to provide lower-cost forms of help to older youth. Since older youth are more capable of reciprocity, we propose that some alloparental aid acts as an investment in future reciprocal relationships or as indirect investment in a relationship with the beneficiary's relatives. Our results support kin selection and relationship effort explanations for who helps Tsimane youth.