ABSTRACT
Humans probably reason by extracting information from repeated observations, building beliefs, or hypotheses that they adjust over time. This process based on probabilities estimations is logical. However, not all decision can be said to be rational and economists have investigated several decisional biases in humans. Some of these biases also exist in non-human primates and this finding raises the question of the evolutionary origins of our decisions. Decision making under risk has been particularly investigated as it concerns a broad sample of decisions with a survival value. Our work aimed at quantifying these biases using economical models, under risk and ambiguity. We also showed that, in an “easy” gambling task, individuals could decide based on probabilities. However, they use heuristics (simplified decision rules) when the task becomes more challenging. Under uncertainty, we showed that two species of great apes could use a process resembling conditional probabilities used by humans.
