International Journal of Primatology, Vol. 18, No. 5, 1997 Comparison of Development and Life History in Pan and Cebus Dorothy M. Fragaszy1-3 and Kim Bard2 Received October 28, 1996; accepted December 10, 1996 We examined growth and development in capuchins and chimpanzees in relation to weaning, onset of reproduction, and reproductive life span. Striking differences are evident in neurobehavioral status at birth (more mature in capuchins), the relative duration of infancy (longer in chimpanzees), and the proportional weight of the infant at the time of weaning (greater in capuchins). Although capuchins and chimpanzees spend a similar proportion of life in a weaned but reproductively immature state, chimpanzees spend so much more of their lives as nursing infants that reproductive output per individual is much lower than in capuchins. Discussion centers around tolerated transfers of food (food-sharing) as a potential adaptation to limited foraging success by immature foragers. Perhaps food transfers from adult to infant, which is a more prominent feature of behavior in chimpanzees than in capuchins in natural environments, allow a very small weanling chimpanzee to survive. KEY WORDS: capuchins; chimpanzees; growth; reproduction; weaning. INTRODUCTION Capuchins (Cebus spp.) and chimpanzees (Pan troglodytes) are widely separated phylogenetically. Capuchins are New World monkeys, in the fam- ily Cebidae; chimpanzees are great apes, in the family Pongidae, and more closely related to Old World monkeys (Cercopithecidae) than to New World monkeys. Capuchins and chimpanzees differ in body size, anatomy, 'Department of Psychology, University of Georgia, Athens, Georgia 30602. 2Yerkes Regional Primate Research Center, Emory University, Atlanta, Georgia 30322. 3To whom correspondence should be addressed at Department of Psychology, University of Georgia, Athens, Georgia 30602. e-mail: cmspsy37@uga.cc.uga.edu. 683 0164-0291/97/1000-0683$12.50/0 6 1997 Plenum Publishing Corporation