Social tool use
Social tool use is the use of manipulation or cooperation to achieve a desired result, and is an important part of primate interactions.
Why orang-utans? Why mother-offspring pairs?
Orang-utan adult pairs have been found to exchange tokens when an individual possesses tokens that were useless for it but that the other individual could exchange for food. Orang-utans were much more likely to donate tokens compared to chimpanzees, gorillas and bonobos when tested. Thus, orang-utans seem to be a promising species to explore social tool use. In this study by Völtera et al mother–offspring pairs were chosen because while mothers are physically stronger than their young, there is great tolerance between them.
The hypothesis
Creating a situation in which mothers have no direct physical control over their offspring may transform the mother’s social tool use from manipulative to a cooperative activity.
Manipulation
Mothers manipulate their offspring to obtain a reward
Initial experiments performed by the group established that the orang-utan mothers manipulated their offspring to retrieve out-of-reach food rewards (offspring retrieve food and mothers steal and eat it) and tools (offspring retrieve tool and mothers steal it, unlock food reward and eat it).
Cooperation
Mothers cooperate with their offspring
Völtera et al then set up an experiment in which mothers had a tool but only offspring could use it to release a food reward for both. In this experiment mothers cooperated with their offspring by passing them the tool. In a variation on this experiment only the offspring received a food reward. In this case mothers’ motivation for cooperation declined, however most mothers continued to pass the tool over to their offspring.
Finally
In summary, these behavioural experiments showed how orang-utan mothers switched from manipulation to cooperation to achieve their goals, some even continuing cooperation when the benefit was not mutual.
References
Christoph J. Völtera, Federico Rossanoa, Josep Calla. (2015). From exploitation to cooperation: social tool use in orang-utan mother–offspring dyads. Animal Behaviour. 100, 126–134.
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