Hans-Peter Kohler received his M.A. in Demography (1994) and Ph.D. in Economics (1997) from the University of California at Berkeley. He is currently head of the research group on Social Dynamics and Fertility at the Max Planck Institute for Demographic Research in Rostock and part-time professor at the University of Southern Denmark in Odense. His primary research interest is processes of social interactions and their relevance for fertility and AIDS-related behaviors in developing and developed countries. Hans-Peter Kohler is also engaged in research on lowest-low fertility levels, the