Do we need to reclassify the social systems of gregarious apes?

Abstract

Decades of research have led to a solid understanding of the social systems of gregarious apes: chimpanzees, bonobos, gorillas, and gibbons. As field studies have increasingly collected data from multiple neighboring habituated groups, genetic and social interconnections have been revealed. These findings provide a more nuanced picture of intergroup relations in apes, and have led to claims in the literature that some ape taxa have multilevel societies. A multilevel society is defined as a nested collection of social entities comprising at least two discernible levels of social integration between the individual and the population. We argue that the evidence for multilevel sociality sensu stricto in apes is currently inconclusive and that it is premature to abandon the traditional classification of ape social systems. However, available findings appear to be consistent with the existence of some degree of higher social grouping patterns. We propose the term supra‐group organization which may adequately capture ape social systems when viewed from a top‐down perspective.

The evolution of peace

“…As pointed out by Glowacki, some primate taxa exhibit peaceful encounters between groups (e.g., western gorillas, Forcina et al, 2019;white-handed gibbons, Reichard & Sommer, 1997) and even cooperative interactions (bonobos, . However, as Glowacki notes, these tend to be transient (Grueter & Wilson, 2021). Rudimentary forms of interdependence resembling durable positive-sum relationships do seem to occur in species that feature multilevel societies.…”

The multilevel society of proboscis monkeys with a possible patrilineal basis

“…Other taxa presenting MLS are generally absent in the immediate phylogenetic neighborhood of taxa presenting MLS, though evidence is inconclusive in some cases (Grueter & Wilson 2021). Thus, great apes are not ideal models to reconstruct MLS in humans (but see Morrison et al 2019).…”

“…By studying the characteristics of MLS in distantly related species we can understand what environmental conditions and/or potential selection pressures are associated with such traits in different lineages. MLS are generally absent in the primates most closely related to humans (i.e., the great apes), although evidence is inconclusive in some cases (Grueter and Wilson 2021; but see Morrison et al 2019). Consequently, studies on primates that are phylogenetically distantly related but exhibit multilevel structures are important for elucidating the evolutionary paths leading to MLS in humans (Grueter et al 2012a).…”

Social and economic interdependence as a basis for peaceful between-group relationships in nonhuman primates and humans

“…As pointed out by Glowacki, some primate taxa exhibit peaceful encounters between groups (e.g., western gorillas, Forcina et al, 2019; white-handed gibbons, Reichard & Sommer, 1997) and even cooperative interactions (bonobos, Tokuyama, Sakamaki, & Furuichi 2019). However, as Glowacki notes, these tend to be transient (Grueter & Wilson, 2021). Rudimentary forms of interdependence resembling durable positive-sum relationships do seem to occur in species that feature multilevel societies.…”