Tuesday, December 3, 2013

Applying Theory to Our Closest Relatives: The Chimpanzee and the Bonobo

I thought I would take a stab at combining both my Anthropology and Psychology majors (as well as my hopes in pursuing graduate school for animal behavior in the next few years) to create an interdisciplinary piece.

Cultural Ecology plays a major role in social organization not only in humans, but even in more advanced species of animals. An interesting example is the contrast between the two most closely related species to humans: chimpanzees and bonobos. Chimpanzees and bonobos share 99% of their DNA with humans, and are more closely related to us and each other than they are to gorillas or any other species of ape. However, despite being so closely related, their social structures are entirely different.

Chimpanzees have a prominent social hierarchy established, in which male dominance plays an important role. The sole function of sex is reproduction, and male chimpanzees will resort to infanticide of unrelated offspring. The purpose is to remove potential competition for their own offspring and to encourage the now available and unoccupied mothers to reproduce with them more readily. Bonobos, on the other hand, are much more egalitarian. A major function of sexual activity in bonobo groups is to solidify social bonds with all members of group, regardless of age, sex, or relatedness. Bonobos use sex to relieve tension, elicit social or food benefits, to greet others, and resolve conflicts. Paternity is largely unknown and females are extremely protective of each other, so instances of infanticide in bonobos are almost unheard of. But how do we explain these social differences between the chimpanzee and the bonobo?

     
Bonobos grooming each other intimately

Chimpanzees in a violent conflict!

Evolutionary anthropologists turn to cultural ecology, examining the habitats and environmental niches each species occupies. Both chimpanzees and bonobos live along the Zaire River, chimpanzees, on the north side, and bonobos, on the south side. About 2.5 million years ago, a drought on the southern side of the river wiped out much of the plant food of gorillas. The gorillas left the south, and the chimpanzees that lived there no longer had competition for fruit and the fiber-rich food that the gorillas used to eat which had grown back. These chimpanzees developed larger, more stable groups with strong social bonds. These southern chimps evolved into what we now know as bonobos. On the north side of the river, the chimpanzees and gorillas continued to share their environmental niche, having no access to the fiber-rich food of the gorillas. They were only able to eat fruit and occasionally meat, both resources that are few and far between. They were required to spend much more time looking for food, not having the time to foster strong social bonds.

In one study, researchers stated that these behavioral differences may even have an effect on cognitive skills. Because bonobos are more cautious and socially tolerant, they tend to be more skilled at solving problems related to theory of mind or an understanding of social causality. Because chimpanzees are more dependent on extractive foraging, they tend to be more skilled at tasks related to tool use or an understanding of physical causality.This study assumed that their mental structures were similar because of their genetic closeness, having only diverged from each other 1-2 million years ago.

However, through the use of neuroimaging technology, more recent research suggests that chimpanzees and bonobos have actually developed different neuroanatomical structures. Bonobos have a more developed limbic system, which includes the amygdala, hypothalamus, and anterior insula—critical regions for emotions and empathy. Bonobos also have a larger pathway connecting the amygdala to the prefrontal cortex of the brain. "When our amygdala senses that our actions are causing someone else distress, we may use that pathway to adjust our behavior in a prosocial direction." Chimpanzees have more highly developed visual system pathways in the brain, which has proven critical in tool use (as suggested in other research).

I think that this is an explanation that structuralists would be more comfortable with. Applying Saussure’s “langue vs. parole,” the langue could be the differences in mental structures and the parole would be the differences in social behavior that resulted from these differences. Levi-Strauss stressed the importance of environment, suggesting that beings create their intellectual world using the materials in their environment. However, he still maintained that this was a product of underlying mental structures. On the other hand, Sapir and Whorf might suggest that the differences in social behavior and communication are determined by the differences in “cultural” patterns. I won’t get into the debate about whether animals have culture (the subject of my First Year Seminar 3 years ago!), but applied here, this could mean that mental structures were determined by the social interactions and behavior, which was a result of the environment they had, the most similar to the cultural ecology perspective.  

-- Mariah!

Further reading:


1 comment:

  1. Thank you for sharing this fascinating information and connecting it to cultural ecology!

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