1. Department of Biology, Georgia Southern University, Statesboro, Georgia 30458.
2. University of Stirling, Department of Psychology, Faculty of Natural Sciences, Stirling FK9 4LA, Scotland.
3. Centre de Primatologie, Centre International de Recherches Médicales de Franceville (CIRMF), B.P. 769 Franceville, Gabon.
4. Durham University, Department of Anthropology, Durham, DH1 3LE, U.K.