1 Centre for Social Learning and Cognitive Evolution, School of Psychology and Neuroscience, University of St. Andrews, St. Andrews KY16 9JP, United Kingdom; a.whiten@st-andrews.ac.uk.
2 Department of Ecology and Evolutionary Biology, University of California, Irvine, CA 92697.
3 Department of Biology, Stanford University, Stanford, CA 94305.
4 Centre for Social Learning and Cognitive Evolution, School of Biology, University of St. Andrews, St. Andrews KY16 9JP, United Kingdom.