Philosophy, Science, and Politics of the Sex Binary

The sex binary—dividing human beings into two discrete categories of male and female—has long been treated as a natural and self-evident fact. Framed as biologically determined and universally applicable, this model continues to shape medical classifications, legal definitions, scientific research, and everyday social interactions. At the same time, a growing body of feminist, scientific, and philosophical work has drawn attention to the instability and contingency of binary sex classifications. Critics have shown that the binary model often fails to account for the diversity of human bodies and identities, and that it serves to reinforce broader systems of social hierarchy and exclusion. Despite these critiques, the sex binary remains a site of deep political, scientific, and cultural investment, particularly as appeals to biology are frequently used to defend its legitimacy. This dissertation takes up these tensions by examining how the sex binary is constructed, contested, and reimagined across science, philosophy, and policy making. The first chapter offers a historical and philosophical account of the sex binary, tracing its religious, cultural, and legal foundations and outlining how feminist theory has sought to destabilize it. Chapters two through four examine how contemporary research in biology, psychology, and neuroscience has been mobilized to support or resist binary models of sex. These chapters show that although some scientific research continues to assert essential differences between males and females, a growing body of empirical work in each of these fields undermines the coherence of the binary model. Moreover, I show that the scientific debates on the sex binary are deeply shaped by social values, revealing the limitations of the value-free ideal of science. The final two chapters address key issues in the philosophy of science and policy making and consider how these debates intersect with public discourse on sex classification. Chapter five analyzes the new demarcation problem and evaluates whether the norm-based approach can help assess the legitimacy of value influences in scientific controversies about the sex binary. I argue that while different approaches to address the new demarcation problem, including the norm-based approach, are valuable, they remain insufficient for fully resolving the underlying tensions. Chapter six turns to the broader implications of this impasse. In the absence of definitive scientific consensus on the sex binary, and amid ongoing philosophical debate over the appropriate role of values in science, I propose turning to new resources that can meaningfully contribute to the conversation. Drawing on feminist and intersex movements, I argue that advocacy and activism are important sources of critical insight, moral imagination, and democratic engagement in efforts to rethink and reframe how we approach sex classification in science and policy making.