Between the recent feminist interest in relocating posthumanism through animal becomings and the emerging field of trans studies, there arise new possibilities for theoretical exchange between the “post” and the “trans.” This article considers how the fields of feminism, trans studies, and posthumanism are actively transforming our thinking around “sex” and “the human.” It proposes that these theoretical approaches are affectively conjoined in their challenge to the concept of preternatural gender as a defining aspect of human-centered sociality. This is because sex and humanity are coconstitutive categories inviting political engagement, especially since the birth of the human in secular, modern thought, beginning with the scientific revolution, as the point at which the human began to break away from the divine. The newly formed concept of humanity that emerged in the seventeenth century was contingent on a highly structured, essentialist conception of sexual difference. On the one hand, the development of the human was explained through a break with the animal in hypotheses about the shift from animal sociality to human civilization; but, on the other, sociobiological theories—pre- and post-Darwin—sought to explain the human “in nature.” Both, however, contained essentialist conceptions of sexual difference in order to articulate the human, whether in its difference to or continuity with the animal. By contrast, posthuman and trans becomings have produced new configurations of bodies that are changing the way we conceptualize human, animal, nature, and culture.