For example, first visiting all locations close to the starting point, then moving farther afield may work. There's no guarantee, however, that such a strategy works in every possible case. Indeed, proceeding from the origin to the nearest point, then to the nearest point to that, and so on doesn't generally give the shortest path. Problems similar to the traveling salesman problem crop up in many practical situations, such as designing networks to link an array of points, routing telephone calls, allocating resources, setting timetables and schedules, planning budgets, and packing objects in bins. In the May 29 Nature , Audrey E. Cramer and C.R. Gallistel of the University of California, Los Angeles report that, rather than always heading for the nearest food supply, the monkeys apparently plan their next three visits to minimize distance and travel time.
Vervet monkeys eat fruit of various kinds, foraging on patchily distributed supplies.
They typically visit several sites in a single trip. To find out, the researchers modeled their experiment on one performed more than two decades earlier with chimpanzees. Psychologist Emil W. Menzel of the State University of New York at Stony Brook carried juvenile chimpanzees around an outdoor field while he hid fruit in 18 randomly placed locations. He then released the chimps and recorded the routes taken to collect the fruits. The apes remembered most of the hiding places and the type of food in each, and they rarely rechecked a place they had already emptied of food.