1. Cell and Developmental Biology, University College London, Gower Street, London WC1E 6BT, UK
2. Research Centre in Evolutionary Anthropology and Palaeoecology, School of Natural Sciences and Psychology, Liverpool John Moores University, Byrom Street, Liverpool L3 3AF, UK
3. Human Origins Research Group, Earth Sciences Department, Natural History Museum, Cromwell Road, London SW7 5BD, UK