Most work on social interactions studies a single, composite effect of interactions within a group. Yet in the case of sexual initiation, there are two distinct social mechanisms-peer-group norms and partner availability-with separate effects and different potential interventions. Here I develop...

We study the long-term determinants of the high rates of HIV infection in sub-Saharan Africa, particularly among women, with a focus on family structure and sexual behavior as shaped by the demographic shock following the transatlantic slave trade. First we show that, in clusters where polygyny...