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.
*For expert commentary on this work, be sure to see the related Dispatch in this issue of Current Biology from Dr. Michael Platt: "Animal Cognition: Monkey Meteorology."
The researchers include Karline R.L. Janmaat, Richard W. Byrne, and Klaus Zuberbühler of the University of St. Andrews in St. Andrews, Scotland, United Kingdom.
This research was funded by the Wenner-Gren and Leakey Foundation, the University of St. Andrews' School of Psychology, the Schure-Bijerinck-Popping foundation of the KNAW, the Stichting Kronendak, the Dobberke Stichting voor Vergelijkende Psychology, the Lucy Burger Stichting, and the Foundation Doctor Catharine van Tussenbroek. In Uganda, the researchers thank the Office of the President, the Uganda National Council for Science and Technology, the Uganda Wildlife Authority, the Makerere University Biological Field Station, and the Kibale Fish and Monkey Project for logistic support and permission to conduct research in Kibale National Park.
Janmaat et al.: "Primates Take Weather into Account when Searching for Fruits." Publishing in Current Biology 16, 1232–1237, June 20, 2006, DOI 10.1016/j.cub.2006.04.031. www.current-biology.com
Related Dispatch by Platt et al.: "Animal Cognition: Monkey Meteorology."