This project examines concepts and theories of the posthuman, or posthumanism, in contemporary popular and theoretical texts. The term "natural perversions" is an apparent paradox, but one that can point to some of the contradictions inherent in humanism; its use here suggests some of the profound challenges posthuman theory presents to exploitative institutions and power structures based on human privilege. Natural perversions is an attempt to naturalize, in a sense, the notion of perversion, but also to turn the nonnative language of perversion back onto dominant humanist institutions and discourses, especially anthropocentric visions of economics, evolution, and sexuality. Economics, evolution and sexuality are implicated in reiterating and supporting each other in their humanist and anthropocentric attitudes and assumptions. Interrogating humanist assumptions in these three areas of knowledge is increasingly necessary, this study contends, in the face of current environmental, economic and political crises such as pollution, peak oil and global warming. Despite their privileging of a human subject, economics, evolution and sexuality can each be considered inhuman systems from a certain point of view, systems that in the words of Elizabeth Grosz "function beyond or above the control of their participants." This project works to problematize human ideals such as reason and rationality, interrogating whether humans can indeed be distinguished from other beings by their rationality and contending that both man-made and natural economies (such as evolution and sexuality) do not function as rationalized and efficient systems in the ways that human thought has generally envisioned. Humans frequently do not behave in their own rational self interest, a foundational assumption of economic theory. The critical theory and popular texts considered here suggest that exuberant, decadent, luxurious, wasteful, and chaotic systems and economies and natural systems may be paradoxically more productive than highly rationalized ones. / Thesis / Doctor of Philosophy (PhD)