1 Department of Evolutionary Genetics, Leibniz Institute for Zoo and Wildlife Research, D-10315 Berlin, Germany; courtiol@izw-berlin.de melinda.mills@nuffield.ox.ac.uk.
2 Department of Sociology, University of Oxford, Oxford OX1 3UQ, United Kingdom; Nuffield College, University of Oxford, Oxford OX1 1NF, United Kingdom.
3 Department of Sociology, University of Oxford, Oxford OX1 3UQ, United Kingdom; Nuffield College, University of Oxford, Oxford OX1 1NF, United Kingdom courtiol@izw-berlin.de melinda.mills@nuffield.ox.ac.uk.