Martha M. Robbins is Research Associate at the Max Planck Institute for Evolutionary Anthropology. She is coeditor of "Mountain Gorillas: Three Decades of "Research at Karisoke "and" Feeding Ecology of Apes and Other Primates". Christophe Boesch is Director of the Department of Primatology at the Max Planck Institute for Evolutionary Anthropology. He is the author of "The Real Chimpanzee: Sex Strategies in the Forest, "among other books.