1. Center on Social Dynamics and Policy, The Brookings Institution Washington District of Columbia
2. School of Social SciencesNottingham Trent UniversityNottingham Nottingham UK
3. Laboratory of Comparative Ethology, National Institute of Child Health and Human DevelopmentPoolesville Maryland
4. Neuroscience and Behavior Unit, California National Primate Research CenterDavis California
5. Brown SchoolWashington University in St. LouisSt. Louis Missouri
6. Sante Fe InstituteSanta Fe New Mexico