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.