1. Department of Comparative Cultural Psychology, Max Planck Institute for Evolutionary Anthropology, 04103 Leipzig, Germany
2. Institute of Biology, Leipzig University, 04103 Leipzig, Germany
3. Naturalistic Social Cognition Group, Max Planck Institute for Human Development, 14195 Berlin, Germany
4. Department of Brain and Cognitive Sciences, Massachusetts Institute of Technology, Cambridge, MA 02139-4307, USA