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Séminaire primatologie

"In search of ecological rationality in decision making over time and under risk : from non-human primates to human primates"

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Présentation de Francesca De Petrillo, jeune et dynamique doctorante* à l’Université La Sapienza de Rome et à l’Istituto di Scienze e Tecnologie della Cognizione - ISTC-CNR de Elisabetta Visalberghi à Rome.

Elle présentera ses travaux de thèse, surtout sur les singes capucins, et les perspectives de notre collaboration pour mener ses expériences sur la "decision making under risk" chez une population des chasseurs-cueilleurs, les pygmées Aka de la RCA.


ABSTRACT
Individuals must constantly make decisions among multiple options, judging and balancing their costs and benefits. These options are often available at different times (intertemporal choices) or are uncertain (risky choices). When faced with intertemporal choices, individuals have to forsake smaller immediate rewards if they wish to obtain larger benefits in the future.
Other common situations are risky choices, i.e., decisions in which there is a variance in the rate of gains, as for example when betting on a coin toss. In both these kind of choices, according to neoclassical economic theory individuals should choose rationally, maximizing their utility. However, experimental studies have shown that both human and non-human animals deviate from rationality. In fact, they devalue options as they are pushed into the future and they generally avoid risk.
An alternative explanation to this apparent irrational behaviour is provided by the ecological rationality hypothesis, according to which there is a matching between decision mechanisms and the environment in which the different species evolved. This hypothesis is well supported by data on chimpanzees and bonobos tested in both intertemporal and risky choice tasks. These two species showed, in fact, a different behaviour : whereas chimpanzees were able to wait up 122.6 s and were risk prone, bonobos were able to wait only 74.4 s and were risk averse.
These differences are likely explained by their different feeding ecology in the wild : whereas chimpanzees engage in feeding activities whose outcome is delayed or uncertain (i.e., eating fruits, hunting for vertebrate, using tools), bonobos safely rely mostly on herbaceous vegetation, a more constant food source. Here, we aimed to assess whether the ecological rationality hypothesis applies also to capuchin monkeys (Sapajus spp.). We tested capuchins in i) a delay choice task in which they have to chose between a smaller sooner option and a larger delayed option and ii) in a risky choice task in which they have to choose between a "safe", constant option and a "risky", variable option. Capuchins were able to wait up to 80 seconds to obtain a larger delayed option and, similarly to chimpanzees, they were this prone.
This results can be explained in the framework of the ecological rationality hypothesis because capuchins’ feeding ecology involves a series of activities that require high delay tolerance (such as extractive foraging), and risk proneness (since they hunt vertebrates that can strike back, process and eat cashew nut despite its caustic protection, and use tools on the ground where the potential risk of being predated is high). Although the ecological rationality hypothesis is promising, future studies should objectively evaluate which features of feeding ecology (as, for example, diet breadth vs. the percentage of fruit in the diet) are more relevant in shaping decision making in the domain or risk and time.
Moreover, since very little cross-cultural research on temporal and risky preferences have been carried out so far in small-scale societies, we are interested in investigating decision making over time and under risk in the Aka pygmies, a very ancient hunter-gatherer society, by employing the same experiential tasks previously used with apes and capuchins.
The results that will emerge from this investigation will be highly relevant for comparisons with non-human animal preferences, as cultural and/or ecological pressures on temporal and risk sensitivity may mirror evolutionary pressures on these behaviours.

Date et lieu : 15 octobre 2014 à 10h en salle Chevalier - CP 135 - MNHN

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* directeur de thèse : Elsa Adessi, Unit of Cognitive Primatology and Primate Center, ISTC