1. Ashmole, P. (1963). The regulation of numbers of tropical oceanic birds.Ibis 103: 458–473.
2. Axelrod, R., and Hamilton, W. D. (1981). The evolution of cooperation.Science 211: 1390–1396.
3. Bearder, S. K. (1987). Lorises, bushbabies, and tarsiers: Diverse societies in solitary foragers. In Smuts, B. B., Cheney, D. L., Seyfarth, R. M., Wrangham, R. W., and Struhsaker, T. T. (eds.),Primate Societies, Univ. of Chicago Press, Chicago, pp. 11–24.
4. Box, H. O. (1975). A social developmental study of young monkeys (Callithrix jacchus) within a captive family group.Primates 16: 419–435.
5. Brown, J. L. (1987).Helping and Communal Breeding in Birds: Ecology and Evolution, Princeton Univ. Press, Princeton.