In Costa Rica, sex work has been studied for decades from a pre-evolutionary perspective, and often with an underlying patriarchal bias because sex work is seen as a social pathology, ignoring contributions from sociobiology and evolutionary psychology. In this study, we measured the performance of predictions made by the evolutionary model, in a sample of 78 women aged 18 to 81 years, who perform sex work in San José, capitol of Costa Rica, interviewed in 2008. The interviews were based on a questionnaire, respondents were paid for their time, and data were analyzed with the SPSS statistical program. All predictions of the evolutionary; model are met by this sample: the customers are mostly men in reproductive age (29 to 54 years) who pay women for sexual activity even in cases in which they establish an emotional relationship with the workers. The predictions of the model for workers are also met, since they are primarily women of reproductive age (24 to 41 years), 100% charge for their services, and women who are more attractive for their beauty, intellect and education, earn 10 times more than the rest. In the human species, resources can be given in exchange for sexual services, and 98% of these sex workers are women who have no other source of income; besides, 69% have no partner helping them to support their children. The other 31% have a partner but do not receive enough money from him.
