The evolution of skills such as reciprocal altruism, planning, and cooperation requires the inhibition of prepotent responses. Both human and non-human animals often face decisions between options available at different times, but whereas humans apparently tolerate delays of weeks or even months, animals tolerate delays of just a few seconds. However, delay tolerance can vary across species and it is unclear if phylogenetic relatedness, feeding ecology, social structure, or metabolic rate account for this difference. To disentangle these hypotheses we evaluated temporal preferences in capuchin monkeys. Specifically, we presented 16 capuchins with choices between a small immediate reward and a large delayed reward employing an adjusting delay procedure, i.e. varying the delay associated to the larger option across sessions until subjects were indifferent between the two options. Then, we compared their performance with that of the other primate species tested so far with the same procedure. Overall, capuchins showed a considerable delay tolerance, and - as in humans - females showed a greater delay tolerance than males, possibly because of females' less opportunistic foraging style. Furthermore, capuchins performed significantly better than closely related species as tamarins and marmosets, and their performance was not significantly different from that of bonobos and chimpanzees. Capuchins' tool use abilities might explain their comparatively high preference for the delayed option. Thus, our results shed light on the evolutionary origins of delay tolerance supporting the feeding ecology hypothesis. Funded by ISTC-CNR and American Society of Primatologists.
