Carel van Schaik Anthropological Institute & Museum, University of Zurich, CH Title Evolutionary changes in brain size: a focus on costs Abstract Mammals and birds show great interspecific variation in brain size, even after the effects of body size have been removed. Because this variation corresponds to cognitive abilities, it is important to identify the selective agents responsible for it. Most current thinking focuses on the benefits of increased brain size, especially in terms of improved social strategizing or foraging efficiency. However, variation in relative brain size may also be due to variation in the ability to deal with the costs of increased brain size. Because brains are energetically expensive tissue, they should have immediate energetic costs as well as developmental costs. Here, we present a thorough test of these effects using phylogenetically corrected analyses of a new data compilation of mammalian species. We show that larger-brained animals compensate for the increased energetic costs by having higher basal metabolic rates (an index of daily energy expenditure), smaller gastro-intestinal tracts or less investment in other expensive functions, or some combination of these responses. They also take longer to reach reproductive maturity, but compensate for this immediate fitness cost by (i) increased adult survival (and hence, over time, a longer maximum adult lifespan), and (ii) increased infant or juvenile survival (especially by producing larger young). Thus, variation in the ability to deal with the costs of increased brain size explains variation in brain size at least as well as variation in benefits. A large data set on birds provides us with an excellent opportunity to identify parallels and differences with mammals. We will report on the first results of this exercise. [C.P. van Schaik, K. Isler] CV I am interested in social evolution in primates, with special emphasis on how data and models inform the human condition. Specifically, I am interested in the origin of some of the most striking derived traits of humans relative to the great apes: technology and culture, life history, cooperation and sexual behavior (but shy away from language). Current work focuses on the nature of culture in great apes and on elucidating the extent to which great behavior is cultural, in order to explain the absence of cumulative culture in great apes. We study the correlated evolution between cognitive abilities and slow life history and the development of ecological competence in wild orangutans in an attempt to identify the pace-makers for the evolution of slow-paced life histories. Other projects focus on coalitions, and on infanticide and sexual counterstrategies. Selected recent publications van Schaik, C.P., Preuschoft, S. & Watts, D.P. (2004) Great Ape Societies: Structures, bonds and cognition. Pp. 192-210 in: (Russon, A. & Begun, D., eds) The Evolution of Thought. Cambridge University Press. Kappeler, P.M., van Schaik, C.P.(eds) (2004) Sexual Selection in Primates: New and Comparative Perspectives. Cambridge University Press, Cambridge. Kappeler, P.M. & C. van Schaik (2004) Sexual selection in primates: review and selective preview. Pp. 3-23. van Schaik, C.P. , Pradhan, G.R., van Noordwijk, M.A. (2004) Mating conflict in primates: infanticide, sexual harassment and female sexuality. Pp. 131-150. van Noordwijk, M.A. & van Schaik, C.P. (2004) Sexual selection and the careers of primate males: paternity concentration, dominance acquisition tactics and transfer decisions. Pp. 208-229. Zinner, D., Nunn, C.L., van Schaik, C.P. & Kappeler, P.M. (2004) Sexual selection and exaggerated sexual swellings of female primates. Pp. 71-89. Wich, S.A., Buij, R., and van Schaik, C.P. (2004) Determinants of orangutan density in the dryland forests of the Leuser Ecosystem. Primates 45: 177-182. Fox, E.A, van Schaik, C.P., Sitompul, A., Wright, D.N. (2004). Intra- and interpopulational differences in orangutan (Pongo pygmaeus) activity and diet: implications for the invention of tool use. Am. J. Phys. Anthropol. 125: 162-174. van Schaik, C.P. (2004) Among Orangutans: Red Apes and the Rise of Human Culture. Belknap/ Harvard University Press. van Schaik, C.P., Pandit, S.A. & Vogel, E.R. (2004) A model for within-group coalitionary aggression among males. Behav. Ecol. Sociobiol. 57: 101-109. Wich, S.A., Utami-Atmoko, S.S., Mitra Setia, T., Rijksen, H.D. Schürmann, C., van Hooff, J.A.R.A.M. & van Schaik, C.P. (2004) Life history of wild Sumatran orangutans (Pongo abelii). Journal of Human Evolution 47: 385-298. van Noordwijk, M.A. & van Schaik, C.P. (2005) Development of ecological competence in Sumatran orangutans. American Journal of Physical Anthropology 127: 79-94 Institution address Carel van Schaik Anthropologisches Institut & Museum Universität Zürich-Irchel Prof. Dr. C. van Schaik, Director Gebäude B42, Stock K Winterthurerstrasse 190 CH-8057 Zürich Tel. ++41 44 635 54 10 Fax ++41 44 635 68 04 vschaik@aim.unizh.ch http://www.aim.unizh.ch/Members/vanschaik.html