1. Centre for Evolutionary Biology, School of Biological Sciences, University of Western Australia, Crawley, WA 6009, Australia
2. Department of Biology, University of Copenhagen, 1165 København, Denmark
3. Department of Comparative Language Science, University of Zurich, Zurich 8006, Switzerland
4. Center for the Interdisciplinary Study of Language Evolution (ISLE), University of Zurich, Zurich 8006, Switzerland
5. Department of Psychology, University of Warwick, Coventry CV4 7AL, UK