Natural selection shaped motivational systems to produce behaviors that increase survival and reproductive fitness during waking life. A dream production mechanism that reflects these motives and simulate them repeatedly in a variety of scenarios during sleep would have increased the probability of survival and reproductive success. A thematic analysis of 900 dream reports suggest that dreaming is a simulation of ancient social motives to rehearse functional behavior aimed at satisfying these motives, and thus provide support to the social motive simulation hypothesis of the function of dreaming.