Dominance and Leverage in Primates

Part Of: Politics sequence
Content Summary: 1000 words, 5 min read

Dominance and Fitness

In many species, dominance hierarchies are fairly easy to measure. Submissive chimpanzees, for example, emit pant-hoots to dominants, which clarify their relationship. Systematically counting these events in a community, and the latent social structure will reliably reveal itself. 

The Elo rating system, used in chess, is an efficient method to estimate rank. Just as chess harnesses observable outcomes (game results) to estimate a hidden variable (player ability), researchers use Elo to estimate latent status from observable pant-hoots:

Intrinsic dominance is underwritten with physical strength, or resource holding potential (RHP). A dramatic illustration of this is lekking behavior, with males gathering in one area and physically competing for prime real estate (near the center). These examples of contest competition amongst male can be deadly, especially among species with sexual selected weapons like antlers on red stags.

Here we illustrate a lek amongst sage-grouse. Females enter the lek and preferentially, although not exclusively, mate with high status males. High status males thus enjoy reproductive benefits, and the species exhibits strong reproductive skew. It is sometimes difficult to verify paternity via behavioral measures alone, but new genetic approaches confirm the hypothesis that dominance bestows fitness benefits (Di Fiore 2003). 

In many species, physical formidability is the primary determinant of dominance. But other species feature political microcoalitions, where multiple subordinates forge alliances to challenge the status of a dominant. For example, de Waal (1982) describes this in a triangular relationship amongst chimpanzee males. After the alpha Yeroen is displaced by a strong Luit, he forms a coalition with the young Nikkie, who together displaced a physically stronger Luit. While his intrinsic dominance was lower, Nikkie’s derived dominance (Hand 1986) propelled him into an alpha position.

Dominance vs Leverage

Yet, there is more to power than dominance. You can see this in the relationship between Nikkie, Yeroen and Luit. Despite being beta, Yeroen engaged in more mating activity than Yeroen. Alphas normally interfere in subordinate mating, but Nikkie did not. Why?

While Nikkie possessed dominance, his position was dependent on Yeroen. Yeroen had leverage over Nikkie, at least until Nikkie’s power was consolidated during his second year. 

We can define leverage as dependence-based power, with a unique resource exchanged for a common resource. This phenomenon is largely independent of dominance rank:

  • Estrus vs Food Tolerance. During estrus, female primates experience advantageous changes in their relationships without changing rank, because their eggs represent an inalienable commodity. Male food tolerance transiently increases – sexual associations could end if males refused to share food (Van Noordwijk and van Schaik 2009).
  • Foraging Skill vs Grooming. Stammbach (1988) reported an experiment in which a single subordinate male long-tailed macaque was trained to use a relatively complex procedure to obtain food. Once he had completed the task, other animals had access to food. As a result, the trained animal began to receive significantly more grooming. The trained animal received significantly more grooming than before the training, which suggests that he had leverage independent of his dominance rank.
  • Infant Access vs Grooming. Monkeys, particularly females, find young infants extremely attractive, and frequently approach and try to interact with the newborn infant. Some mothers will grant access to their newborns in exchange for such access (Silk, 2002).

The taxonomy of Smith et al (2002) delineates these different facets of power (a.k.a., status). This aligns with certain sociological theories of power in humans (Emerson 1962), as argued in Chapais (1991).

Primate status is promoted by competence. Dominance requires not just physical formidability, but skill in coalition formation, tactical deception, and combat tactics. Similarly, leverage isn’t restricted to resource ownership – foraging skill can be another route to power. 

Dominance Produces Leverage

But dominance and leverage are not independent. Dominance is itself a unique resource, which can in turn produce leverage.

Alphas often engage in bridging alliances, where a dominant backs a subordinate to increase his derived dominance rank. More generally, Seyfarth (1977) proposed the grooming for support model, with three subcomponents. 

  1. Status Attraction: grooming directed up the dominance hierarchy. Supportive results in Tiddi et al (2012), Schino (2001). But in other species, grooming can be directed downwards (Parr et al 1997, Saunder 1988), or in no specific direction (Silk et al 1999).
  2. Grooming Reciprocity: dominants were more likely to support subordinates. Supportive results in Seyfarth & Cheney (1984), Hemelrijk (2004)
  3. Affiliative Competition: subordinates compete for grooming access to dominant. Supportive results in Schino (2007).

Dominants have leverage! Here they exchange a unique resource (coalitional support) for common resources (grooming). 

The status attraction phenomenon shows that subordination is more than unalloyed fear and avoidance. Primate dominance thus exhibits a kind of proto-prestige (admiration for the powerful), which is quite elaborate in Homo Sapiens. 

Other resources besides dominant-provided political support can generate leverage. Grooming for food tolerance exchanges are documented in Henzi et al (2003)Subordinate support for sexual tolerance exchanges are documented in Duffy et al (2007).  Besides these dyadic exchanges, alpha chimpanzees also produce public goods. They engage in dispute resolution (a proto-judiciary!), impartially prying apart disputants to keep the peace, and underdog advocacy to protect the weak. These public goods may also provide leverage. 

Until next time.

References

  1. Chapais (1991). Primates and the origins of aggression, power, and politics among humans.
  2. Chapais (2015). Competence and the evolutionary origins of status and power in humans
  3. Di Fiore (2003). Molecular genetic approaches to the study of primate behavior, social organization, and reproduction
  4. Duffy et al (2007). Male chimpanzees exchange political support for mating opportunities
  5. Emerson (1962). Power-Dependence Relations
  6. Hand (1986). Resolution of social conflicts: dominance, egalitarianism, spheres of dominance, and game theory.
  7. Henrich & Gil-White (2000). The evolution of prestige: freely conferred deference as a mechanism for enhancing the benefits of cultural transmission
  8. Henzi et al (2003). Effect of resource competition on the long-term allocation of grooming by female baboons: evaluating Seyfarth’s model
  9. Hemelrijk (2004) Support for being groomed in long-tailed macaques
  10. Lewis (2002). Beyond dominance: the importance of leverage
  11. Newton-Fisher (2017). Modeling Social Dominance: Elo-Ratings, Prior History, and the Intensity of Aggression
  12. Parr et al (1997). Grooming down the hierarchy: allogrooming in captive brown capuchin monkeys
  13. Saunder (1988). Ecological, social, and evolutionary aspects of baboon (Papio cynocephalus) grooming behavior
  14. Schino (2001). Grooming, competition and social rank among female primates: a meta-analysis
  15. Schino (2007). Grooming and agonistic support: a meta-analysis of primate reciprocal altruism.
  16. Seyfarth (1977). A model of social grooming among adult female monkeys
  17. Seyfarth & Cheney (1984). Grooming, alliances, and reciprocal altruism in vervet monkeys
  18. Silk et al (1999). The structure of social relationships among female savannah baboons in Moremi Reserve, Botswana.
  19. Silk (2002). Using the ‘f’-word in primatology.
  20. Stammbach (1988). Group responses to specially skilled individuals in a Macaca fascicularis group
  21. Tiddi et al (2012). Grooming up the hierarchy: the exchange of grooming and rank-related benefits in a New World primate.
  22. Von Noordwijk & van Schaik (2009). Intersexual food transfer among orangutans: do females test males for coercive tendency? Maria A. van Noordwijk & Carel P. van Schaik

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