School of Human Evolution and Social Change, Arizona State University
April 14, 2016 10:30, A 706/707
Human have multi-level social and mating systems, where smaller social units (e.g., bands) are nested within larger ones (e.g., the ethnolinguistic tribe), and most marriages occur between member of different bands within the same tribe. The evolution of human multi-level sociality is puzzling from a phylogenetic perspective, as closely related species should have similar social and mating systems, with certain systems only evolving if the necessary building blocks were already present in ancestral species.
I use long-term data from the Ngogo community of chimpanzees in Kibale National Park, Uganda, to show that some of the building blocks for the evolution of multi-level sociality in humans may indeed be present in the social and mating systems of our closest living relatives. Previous research at Ngogo has shown that males and females do not utilize the entire community’s territory evenly, but instead show long-term tendencies to selectively range in certain areas of the territory (i.e., neighborhoods), where they frequently associate and reproduce with preferred partners. Here I show that unlike at most other chimpanzee communities, many females remain at Ngogo to reproduce instead of dispersing to a new community. In addition, many of these females disperse from their natal neighborhood (which contains many close male relatives) to reproduce in another neighborhood (which contains few male relatives) within the Ngogo community. This phenomenon of “within-community dispersal”, previously undescribed in chimpanzees, allows females to effectively reduce the potential costs of inbreeding while retaining the benefits of continued membership in their natal community.
This research was funded by Arizona State university, Boston University, the Max Planck Society, and the Leakey Foundation.