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Patriarchal Chimpanzees, Matriarchal Bonobos: Potential Ecological Causes of a Pan Dichotomy

  • Volker SommerEmail author
  • Jan Bauer
  • Andrew Fowler
  • Sylvia Ortmann
Chapter
Part of the Developments in Primatology: Progress and Prospects book series (DIPR, volume 35)

Abstract

Chimpanzees and bonobos, despite being closely related hominoid primates, differ in female gregariousness and dominance style. Violent male aggression is not atypical in chimpanzee societies and is vented against both other males and females in intra- as well as inter-group conflicts; relationships amongst females are rather weak. Bonobo societies, on the other hand, are female-centred; reports[Comp1] about inter-group conflict are rare to absent but there are numerous reports of blood-drawing injuries inflicted upon males by coalitions of females.

This dichotomy is of potential interest for the understanding of social dynamics in contemporary human societies, too, given that Pan and Homo shared a last ­common ancestor 5 – 6 million years ago. For example, political agendas to achieve a greater equality of the sexes might have to work against our natural inclinations, if the last common ancestor exhibited the patriarchal tendencies found in chimpanzees. Vice versa, if the last common ancestor possessed the matriarchal tendencies of bonobos, then patriarchal tendencies in contemporary human societies could be understood as rather recent cultural developments that can be more easily undone by counter-measures, i.e., changes in socio-economic dynamics.

Such assertions are not unproblematic, given millions of years of evolution. Nevertheless, a reconstruction of the ancestral roots of the behavioural suites of Homo and Pan will have to rely on a causal understanding of the different species psychologies of chimpanzees versus bonobos. These should in some ways be related to ecology. Both species have a mixed diet dominated by fruit with a similar composition. To test if their diet differs in availability and quality, we collected data on habitat phenology and analysed nutritional content of food plants and non-food plants from a community of bonobos in Salonga National Park, Democratic Republic of Congo, and a community of chimpanzees living in Gashaka Gumti National Park / Nigeria.

We found that chimpanzee diet is more diverse, whereas bonobos can rely on a few staple species for longer periods of time – which reflects the more seasonal climate at the chimpanzee site. Both species prefer fruit with elevated contents of water, sugar and fat, but chimpanzees have to cope with much higher levels of anti-feedants such as tannins. Moreover, only bonobos have access to a herb with low levels of fibre but high protein. In addition, chimpanzees invest more time and energy in the removal of seeds from fruit and in digestion. The costs of acquisition of high quality food are thus higher in chimpanzees than in bonobos. The greater constraints in terms of food availability and quality are reflected in greater levels of female-female competition as evidenced by consistently lower levels of gregariousness in chimpanzees measured through the size of nest groups.

Thus, local ecologies can modify social behaviours. However, support for the hypothesis that ecological differences are at the heart of the dichotomy of sociality in Pan is not unequivocal because of considerable intra-specific variability throughout the geographical range of bonobos and, in particular, chimpanzees with respect to social processes and fluctuating parameters of flora, fauna and climate. Accordingly, future studies will have to explore the extent of this flexibility and if and how it covaries with local ecologies.

Keywords

Pan troglodytes Pan paniscus Matriarchy Food quality 

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Authors and Affiliations

  • Volker Sommer
    • 1
    Email author
  • Jan Bauer
  • Andrew Fowler
  • Sylvia Ortmann
  1. 1.Department of AnthropologyUniversity College LondonLondonUK

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