1. Institute of Behavioral Science, University of Colorado, 1440 15th Street, Boulder, CO 80309-0483, USA
2. Department of Sociology, University of Colorado, 1440 15th Street, Boulder, CO 80309-0483, USA
3. Institute for Behavioral Genetics, University of Colorado, 1480 30th Street, Boulder, CO 80303, USA
4. Carolina Population Center and Department of Sociology, University of North Carolina, 123 W Franklin Street, Chapel Hill, NC 27516, USA
5. Department of Integrative Physiology, University of Colorado, 1480 30th Street, Boulder, CO 80303, USA