To understand the nature of scaling in human societies, we need to understand how humans are able to cooperate in large numbers. This, in turn, requires that we understand cooperation. Cooperation on a large scale is uncommon among non-human animals, and when it does occur, it tends to be of a very different nature than human cooperation.
Fision, Fusion, and Cooperation
Robinson and Barker (2017) analyze cooperation among humans and among ants. They define a group as “aggregation of cooperating individuals that is stable with respect to the timescale of cooperation” and distinguishish between within-group cooperation and inter-group cooperation. The authors identify two key drivers of inter-group cooperation that are common across species: protection against threats, such as predators and harsh climates; and resource sharing. As discussed by Robinson and Barker (2017), there are, in turn, two possible collective responses among multiple groups to shared threats. One response is fusionism, or for multiple groups to fuse into a single group. This behavior is seen among many types of animals, as is not intergroup cooperation under definition of Robinson and Barker (2017). A second response is intergroup cooperation, whereby groups remain distinct.
Wittemyer, Douglas-Hamilton, and Getz (2005) apply cluster analysis to the species Loxodonta africana of elephant and find four tiers of social organization. The lower two tiers are stable across seasons, but the upper two tiers are more prone to fission-fusion dynamics. Smith et al. (2008) identify fission-fusion dynamics among populations of spotted hyenas, with the sharing of resources and protection from lions key drivers of fusion, where aggression is a key of fission. Thus spotted hyena population are set by an equilibrium between the two forces, with populations being larger at times of food abundance.
Drivers and Barriers to Cooperation
Schwartz and Hoeksema (1998) argue that, under the model of comparative advantage, geographic differences in the distribution of resources should drive mutualisms. Here, a “mutualism” is a mutually beneficial biological interaction between individuals, and as the paper uses plants and mycorrhizal fungi as an example, mutualisms are not necessary conscious cooperation. Under comparative advantage, if two distinct groups can produce two distinct resources at different relative costs, then it is advantageous for the two groups to trade, provided that transaction costs are low. Furthermore, intergroup trade would lead to specialization among the different groups.
However, Robinson and Barker (2017) argue that this phenomenon is rare among nonhuman animals, and indeed, specialization across groups is what makes human intergroup cooperation unique.
Another example of a driver of cooperation is advantage in mating. Connor et al. (2022) show that male bottlenose dolphins in Shark Bay, Western Australia form the largest known multilevel alliance network outside of humans, with unrelated males cooperating across three alliance levels. The study shows that cooperation between groups, not just within them, increases male access to females. The authors argue this represents a striking case of convergent evolution with human intergroup alliance behavior. Connor et al. (2022) reach their conclusion by tracking the association behavior of 121 male dolphins.
Smith et al. (2012) consider cooperation in terms of hunting. Consider 87 species of carnivores, an order of mammals, they find a positive relationship between a carnivorous diet and cooperative behavior. Spotted hyenas, in particular, show high levels of social hunting and cooperating with nonkin individuals.
The Role of Relatedness
Powers and Lehmann (2017), discussed at greater length elsewhere, consider large-scale cooperation from a genetic perspective and propose three mechanisms to drive it: that organisms gain directly from cooperation, that organisms gain indirectly through reciprocity, and that organisms propagate their genes through large scale cooperation when large numbers of individuals are related. Since insects tend to be related to many other individual insects, the third mechanism might explain large scale insect cooperation, such as among ants as discussed by Robinson and Barker (2017). Reeve and Hölldobler (2007) model cooperation among insects as a dynamic between individual cooperation between groups and intergroup cooperation, and they find that intergroup cooperation increases as the level of relatedness between groups increases. However, they also find that intergroup competition is a driver of within-group cooperation. Wilson and Hölldobler (2005) reach the same conclusion in studying eusocial insects, such as ants and termites.
Samuni, Crockford, and Wittig (2021) track intergroup relations between chimpanzees and find that intergroup cooperation is more likely to occur among related individuals than between unrelated individuals. They furthermore find that social bonds increase levels of cooperation between both kin and non-kin individuals.
Although relatedness helps explain cooperation among nonhuman animals, it is not strictly necessary. Bernasconi and Strassmann (1999) observe large-scale non-kin cooperation among ant foundress associations (an ant foundress is a queen who founds a new colony), showing that relatedness is not necessary for intergroup cooperation.
The ecological conditions that selected for large-scale cooperation are rare, as argue Rodrigues, Barker, and Robinson (2023), and thus such cooperation is rare. They find that dispersal patterns are a major factor in determining how cooperation unfolds. In local dispersal, individuals do not move far from their birthplace, and this individuals entering a new group are more likely to be kin. In long-distance dispersal, individuals are more likely to travel a long distance from their birth place and thus interact with individuals who are not kin. Species that show more local dispersal are more likely to show intergroup cooperation, which the authors argue is based on relatedness.
However, Rodrigues, Barker, and Robinson (2023) also show that localized dispersal creates a negative feedback to cooperation. Mostly local disperal, also known as high population viscosity, creates additional competition for resources, which undermines intergroup cooperation. For this reason, the authors’ model shows that intergroup cooperation is unstable and thus rare.
What Makes Humans Unique?
Pisor and Surbeck (2019) compare intergroup interactions between humans and nonhuman great apes from an evolutionary perspective, which can take the form of aggression or tolerance. They find that the human foraging ecology, with high variability in the availiability of resources, is especially conducive to intergroup cooperation, which took the form of a greater number of intergroup relationships reinforced by status acquisition and cultural institutions.
References
Robinson, E. J. H., Barker, J. L. “Inter-group cooperation in humans and other animals”. Biology Letters 13(3): 20160793. March 2017.
Wittemyer, G., Douglas-Hamilton, I., Getz, W.M. “The socioecology of elephants: analysis of the processes creating multitiered social structures”. Animal Behaviour 69(6), pp. 1357-1371. June 2005.
Smith, J.E., Kolowski, J.M., Graham, K.E., Dawes, S.E., Holekamp, K.E. “Social and ecological determinants of fission–fusion dynamics in the spotted hyaena”. Animal Behaviour 76(3), pp. 619-636. September 2008.
Schwartz, M.W., Hoeksema, J.D. “Specialization and resource trade: biological markets as a model of mutualisms”. Ecology 79(3), pp. 1029-1038. April 1998.
Powers, S.T., Lehmann, L. “When is bigger better? The effects of group size on the evolution of helping behaviours”. Biological Reviews 92(2), pp. 902-920. May 2017.
Reeve, H.K., Hölldobler, B. “The emergence of a superorganism through intergroup competition”. Proceedings of the National Academy of Sciences 104(23), pp. 9736-9740. June 2007.
Wilson, E.O., Hölldobler, B. “Eusociality: origin and consequences”. Proceedings of the National Academy of Sciences 102(38), pp. 13367-13371. September 2005.
Bernasconi, G., Strassmann, J.E. “Cooperation among unrelated individuals: the ant foundress case”. Trends in Ecology & Evolution 14(12), pp. 477-482. December 1999.
Connor, R.C., Krützen, M., Allen, S.J., Sherwin, W.B., King, S.L. “Strategic intergroup alliances increase access to a contested resource in male bottlenose dolphins”. Proceedings of the National Academy of Sciences 119(36): e2121723119. August 2022
Samuni, L., Crockford, C., Wittig, R.M. “Group-level cooperation in chimpanzees is shaped by strong social ties”. Nature communications 12(1): 539. January 2021.
Pisor, A.C., Surbeck, M. “The evolution of intergroup tolerance in nonhuman primates and humans”. Evolutionary Anthropology: Issues, News, and Reviews 28(4), pp. 210-223. July 2019.
Smith, J.E., Swanson, E.M., Reed, D., Holekamp, K.E. “Evolution of cooperation among mammalian carnivores and its relevance to hominin evolution”. Current Anthropology 53(26), pp. S436-452. December 2012.
Rodrigues, A.M., Barker, J.L., Robinson, E.J. “The evolution of intergroup cooperation”. Philosophical Transactions of the Royal Society B: Biological Sciences 378(1874). April 2023.