1. Itani, J. & Nishimura, A. inPrecultural Primate Behavior (ed. Menzel, E. W. Jr) 26-50 (Karger, Basel, 1973).
2. Watanabe, K. inThe Ethological Roots of Culture (eds Gardner, R. A., Chiarelli, A. B., Gardner, B. T. & Plooij, F. X.) 81-94 (Kluwer, Dordrecht, 1994).
3. Galef, B. G. Hum. Nature 3, 157–178 ( 1990).
4. Premack, D. & Premack, A. J. inCompanion Encyclopedia of Anthropology (ed. Ingold, T.) 350-365 (Routledge, London, 1994).
5. Tomasello, M., Kruger, A. C. & Ratner, H. H. Behav. Brain Sci. 16, 495– 552 (1993).