Chimpanzees lend each other a helping hand


Not only do our ape cousins cooperate, they police bad-behaving members of their own group. Angus Bezzina reports.


Three chimpanzees pull at the cooperation apparatus, while two others look on.
Frans de Waal / Yerkes National Primate Research Centre

We humans might see ourselves as somewhat unique when it comes to putting aside differences and helping each other towards a common goal. But a new study suggests some of our nearest genetic relatives – chimpanzees – might beg to differ.

The work, by Malini Suchak from Canisius College in the US and her colleagues and published in the Proceedings of the National Academy of Sciences, suggests these animals put aside competition for cooperation more often than not.

While intelligent and adept at problem solving, previous studies have shown chimpanzees struggled to work together and often exhibiting intolerance. But these studies tested only a few animals at a time, and never within an entire social group.

To see how well chimpanzees as a group fare, Suchak and her colleagues went to the Yerkes National Primate Research Centre of Emory University where they set up an apparatus in front of two groups of adult chimpanzees.

To get a food reward, at least two chimpanzees had to work together. One had to remove a barrier while another simultaneously pulled in a tray.

If the group was successful with two cooperating individuals, the researchers made the test harder – introducing a second barrier that required a third chimpanzee to get the reward.

The experiment was conducted in hour-long test sessions, two to three times a week.

During these hours the apparatus would be reset after every successful use and the chimpanzees could continue to work the apparatus as many times as they wanted.

The test allowed chimpanzees not working on the apparatus to bump others out the way, or even steal food from those operating the apparatus.

Such behaviour was identified as “competitive” – contrary to cooperation within the group.

During the 94 hours that the groups of chimpanzees were tested the overall rate of cooperation was quite high. Some 3,565 cooperative acts were completed compared to only 600 competitive interactions.

Interestingly, Suchak and her colleagues noticed several enforcement mechanisms used by the chimpanzees to deter members from competitive acts, such as whimpering, pouting, screaming or displaying a silent bared-teeth expression.

They even saw third-party punishment, where a bystander within the group intervened by threatening or hitting the offender or by consoling the victim.

Gisela Kaplan, a behavioural scientist from the University of New England in Australia, notes that these types of activities are quite common – not only with chimpanzees but with great ape species in general.

“There is always a cost to breaking a rule and that cost can be punishment or ostracism, even loss of status,” she says.

“Eventually, the cooperative behaviour will predominate because the price to pay is too high. If you get ostracised by the group, it is not worth it.”

Task partner choice played a significant role in the chimpanzees’ cooperative efforts as they typically only approached other members of their group that were of similar rank or their own kin.

Kaplan says that while the idea of cooperation within great apes is not a new concept, up until now it has been largely neglected.

“Within the group [of chimpanzees] cooperation is important if they are to remain competitive as a whole. So within competition, there has to be a level of cooperation.

“How this actually occurs and how you get the change in behaviour within the group is something that this paper illustrates very nicely.”

  1. http://www.pnas.org/cgi/doi/10.1073/pnas.1611826113
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