The work, which potentially informs our understanding of how cognitive skills developed in humans and other primates, is reported by Karline Janmaat, Richard Byrne, and Klaus Zuberb�hler of the University of St. Andrews in the June 20th issue of Current Biology.

The question of why primates, and especially humans, have more strongly developed cognitive skills than other mammals has a long history in science. The most widely accepted notion has been that primates' superior cognitive abilities have evolved in the social realm. Many primate species live in complex societies, and, the argument goes, this favored the evolution of especially developed social skills.

Although there is much empirical evidence in favor of the social-intelligence hypothesis, very little work has been conducted to address its alternative, the idea that primate cognition has evolved to deal with problems of an ecological nature, such as foraging for food.

With their new work, the researchers sought to address this anomalous gap. By following a group of wild gray-cheeked mangabeys from dawn to dusk over 210 days in their natural rainforest habitat of Kibale Forest, Uganda, the scientists obtained an almost complete record of their foraging decisions in relation to their preferred food, figs.

The data showed that the monkeys were more likely to revisit fig trees (in which they had found fruit before) after a period of warm and sunny days than after a period of cold and cloudy days. Temperature and solar radiation are known to accelerate maturation of fruits and insect larvae inside them.

The researchers were able to show that past weather conditions--as opposed to sensory cues such as the smell of ripe fruit--accounted for the behavioral trend they observed.

These findings are consistent with the idea that monkeys make foraging decisions on the basis of episodic (or "event-based") memories of whether or not a tree previously carried fruit, combined with knowledge of recent and present weather conditions and a more generalized understanding of the relationship between temperature and solar radiation and the maturation rate of fruit and insect larvae.

The findings are also consistent with the idea that the evolution of primate cognitive skills has proceeded, at least in part, as a result of ecological challenges associated with foraging for intermittently available food such as ripening fruit.

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