1. Institute of Zoology, Zoological Society of London, Regent's Park, London NW1 4RY, UK
2. School of Botany and Zoology, Forest Biodiversity Programme, University of Natal, Post Bag X01, Scottsville, Pietermaritzburg 3209, South Africa
3. Department of Anthropology, University College London, Gower Street, London WC1E 6BT, UK