This paper reviews several mid-level theories of sexuality on the theme of changes in sexuality, which is supported by evidence that changes in sexuality occur throughout time, during the course of relationships, and depending on the larger sociocultural context. The first section covers the theory of female erotic plasticity, which suggests that women on average exhibit greater variation in their sexual attitudes, desires, and behavior over the course of their lives than men. The second section addresses changes in passion over the course of romantic relationships. Changes in intimacy within a relationship over time are hypothesized to produce temporary spikes in passion and sexual behavior. The final section reviews the theory of sexual economics, which analyzes sexual behavior according to economic principles. This theory proposes that sex is a female resource that women exchange with men for other valued rewards. Changes in the sexual marketplace affect the negotiation of sex between the genders. Although these changes in sexuality are well-documented, neuroscience research is needed to shed light on how the brain enables, responds, and adjusts to these changes
