Dominance and Social Instability / Wild Male Chimps – Papers


Biopsychosoc Med Click for full paper

The costs of dominance: testosterone, cortisol and intestinal parasites in wild male chimpanzees

Michael P Muehlenbein 1 and David P Watts2

 Clip: Direct associations between testosterone, rates of aggression, and dominance rank have been identified in several species, including nonhuman primates [17,18]. Conversely, several studies have failed to demonstrate significant correlations between aggression, dominance rank and testosterone levels [19,20]. In fact, there is surprisingly little evidence that short-term changes in testosterone levels correlate with increased levels of aggression, and fluctuations in testosterone levels in healthy, eugonadal individuals over time do not necessarily predict changes in levels of aggression within individuals, human or nonhuman [reviewed in [21] and [22]]. Rather, testosterone may have a permissive effect, potentiating pre-existing patterns of aggression [23]. Testosterone is also more frequently associated with aggression and dominance rank during situations of social instability, such as during challenges by conspecific males for territory or access to mates, the establishment of territorial boundaries, the formation of dominance relationships, or in the presence of receptive females [24].



Behav Ecol Sociobiol. Click for full paper

The relationship between testosterone and long-distance calling in wild male chimpanzees


Clip: The purpose of this study was to investigate the relationship between Testosterone production and vocal behaviour in wild male chimpanzees. Chimpanzees live in multi-male, multi-female communities in which individuals form temporary subgroups (“parties”) that frequently change in size and composition (Chapman et al. 1995; Aureli et al. 2008). Chimpanzees produce long-distance “pant hoot” vocalizations that play a crucial role in coordinating grouping in their unstable society (Mitani and Nishida 1993; Fedurek et al. 2014). Because chimpanzees appear capable of recognizing the calls of specific community members (Mitani et al. 1996; Kojima et al. 2003), pant-hoots allow listeners to locate other individuals.

Although male chimpanzees often cooperate with each other, and form strong social bonds (Watts 2002; Mitani 2009), aggressive interactions are also important to the achievement and maintenance of male status (Muller and Mitani 2005). It has been suggested that chimpanzee pant hoots might be involved in male status competition. For example, high-ranking individuals pant hoot more often than low-ranking ones, suggesting that the call signals social status (Mitani and Nishida 1993; Clark and Wrangham 1994; Fedurek et al. 2014). Males often pant hoot in choruses, and such chorusing may facilitate coalition formation against other males (Fedurek et al. 2013a). In addition, pant-hooting rates are elevated on days when between-male competition is high, for example when valuable resources such as oestrous females or high-quality food are available (Fedurek et al 2014). Consequently, male pant hoots, apart from coordinating movements of community members, may play an important signaling role in male-male competition. Although this hypothesis has not been explored in detail, a positive relationship between pant-hooting and T levels would be consistent with this function, since in many animals, ranging from amphibians to mammals, the production of calls associated with mating or territorial behaviour is regulated by T (Floody 1981; Van Duyse et al. 2002; Wilczynski et al. 2005).

Does instability in human male social groups contribute to male aggression? It should be “a no-brainer” to correlate violent eruptions  – gangs, criminal predation, civil wars, religious wars and world wars – and “over the top” political and financial competition, with unstable social conditions. Is this too obvious a conclusion?
If one is living in the U.S. today, current social instability, manifesting as culture wars for over a half-century now, cannot be ignored as the precursor of outbreaks of “serious physical violence” (Civil war) between male “groups” in the near future.

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