2026-05-11 マサチューセッツ大学アマースト校
Abov: Kinda baboons in Zambia. Photo credit: Amanda FuchsTop: Gelada monkeys in Ethiopia. Photo credit: Jacob Feder.
＜関連情報＞
- https://www.umass.edu/news/article/baboon-societies-arent-one-size-fits-all-study-finds
- https://www.pnas.org/doi/10.1073/pnas.2520774123
霊長類の多様な系統において、異なる社会構造はそれぞれ異なる社会規範によって支えられている Disparate social structures are underpinned by distinct social rules across a primate radiation
Jacob A. Feder, Susan C. Alberts, Elizabeth A. Archie, +32 , and Joan B. Silk
Proceedings of the National Academy of Sciences Published:May 1, 2026
DOI:https://doi.org/10.1073/pnas.2520774123
Significance
What forces explain variation in primate societies? While kinship and dominance shape the social lives of many of our close relatives, it is unclear how their effects differ across species. Using a new database comprising decades of field research, we found that baboons and their close relatives fell into three general patterns: one in which groups were cohesive, kin-biased, and moderately rank-biased, another in which groups were more cliquish and nepotistic, and a third in which groups were divided into clusters centered on dominant males. Distinct primate societies may thus reflect differences in the strength of females’ nepotistic biases and the degree of males’ social influence.
Abstract
Over six decades of research on wild baboons and their close relatives (collectively, the African papionins) have uncovered substantial variation in their behavior and social systems. While most papionins form discrete social groups (single-level societies), a few others form small social units that are nested within larger supergroups (multi-level societies). These two systems are generally thought to be qualitatively distinct, but data from wild populations increasingly suggest that there may be areas of overlap. To quantify this potential gradient in social structure, a more systematic, comparative analysis is needed. Here, we constructed a database of behavioral and demographic records spanning 135 group-years, 28 social groups, 13 long-term field studies, and 11 species to quantify variation in grooming network structure and identify the individual and dyadic properties (e.g., kinship and social status effects) that underlie this variation. Consistent with accumulating field observations, the single-level species could be divided into two categories: cohesive and cliquish. Cohesive single-level networks were dense, kin-biased, and moderately rank-structured, while cliquish single-level networks were more differentiated, slightly more kin-biased, and strongly rank-structured. As expected, multi-level networks were very modular and shaped by females’ ties to specific dominant males but varied in their kin biases. Taken together, these data suggest that in the African papionins i) kin and rank biases are widespread but vary in their strength; ii) male-centered subgroups are exclusive to multi-level systems; and iii) increases in network modularity can emerge in response to heightened nepotism and male-centered clustering.
