There are two sexes. Man and Woman.

1. Why some scientists insist on two sexes — a reproductive definition that sounds definitive

Multiple sources ground the two-sex claim in reproductive biology, defining sex by whether an individual produces sperm or ova and framing male and female as the two reproductive classes. An interview-based piece argues that DSDs (differences or disorders of sexual development) do not create additional sexes and that sex, as a biological category, remains binary ^[1]. A separate pro-binary analysis draws on evolutionary arguments — anisogamy in mammals and developmental genetics — to assert that human sex is biologically binary and largely immutable, noting intersex conditions as rare anomalies that do not alter the two-sex framework ^[2]. Those sources treat reproductive capacity and gamete type as the core, non-negotiable criterion for sex classification.

2. Why many researchers call the binary an oversimplification — sex as a bundle of traits

Other scientific analyses argue that defining sex solely by reproductive cells overlooks genetic, hormonal, chromosomal, and anatomical variation. Recent reviews and commentary point out that estimates of DSD prevalence range and that variations in sexual development produce individuals who do not fit neatly into binary categories ^{[3] [5]}. These sources treat sex as a set of correlated traits rather than a single property, showing that biology can yield mosaic patterns — such as atypical chromosomal complements, androgen insensitivity, and variable gonadal development — which complicate a strict two-sex model ^{[6] [4]}. The result is a scientific case for greater nuance in how medical and legal systems categorize sex.

3. The sex–gender distinction nobody asked you to ignore — social identity versus biology

Social-scientific and public-health materials emphasize a clear distinction between sex (biological attributes) and gender (social roles and identity), arguing the binary claim often conflates the two ^{[7] [8]}. Wikipedia-sourced syntheses note cultural variation in gender categories, including third-gender traditions and non-binary identities, and stress that most contemporary agencies separate sex from gender in policy and research ^[9]. This body of work reframes the debate: even if many biological contexts use two categories for practical reasons, gender identity and social recognition are broader and culturally mediated phenomena that do not map perfectly onto binary biological definitions.

4. What prevalence and medical data actually show — rarity, but not irrelevance, of intersex variation

Medical literature offers mixed numbers but consistently shows that intersex/DSD conditions are not vanishingly rare, with some reviews estimating variations in sexual development occurring in roughly 1 in 100 to 1 in several thousand births depending on definitions used ^[3]. Authors caution that prevalence estimates hinge on diagnostic criteria and whether subtle chromosomal or endocrine variations are counted. Pro-binary commentators acknowledge intersex cases as exceptions; others argue these exceptions are biologically meaningful and ethically significant for clinical practice, legal classification, and personal identity ^{[6] [5]}. The practical implication is that policy and healthcare must account for variation even while many systems operate on a binary basis.

5. Competing agendas and how they shape conclusions — science, politics, and advocacy

Analyses invoking a strict binary frequently come from evolutionary or conservative medical frames that prioritize reproductive definitions and clear categorical rules, often to inform policy or clinical guidelines ^{[2] [1]}. Conversely, literature emphasizing a spectrum of sex characteristics often arises in interdisciplinary, clinical, and rights-focused contexts that stress patient variability and social inclusion ^{[3] [4]}. Both approaches rely on legitimate data but emphasize different criteria — reproductive gamete-production versus cumulative trait variability and lived experience. Recognizing these motives explains why the same factual universe yields divergent public claims.

6. Bottom line for policy, medicine, and public conversation — nuance, not slogans

The empirical record supports two widely used reproductive categories (male/female) while also documenting biological diversity that challenges a simplistic binary. For medicine and law, the pragmatic course is to use clear categories where they serve necessary functions, coupled with mechanisms to accommodate individuals whose bodies or identities fall outside the standard pair ^{[8] [3]}. Public debate should separate claims about gamete-based biology from questions of social identity and rights, acknowledge DSD prevalence and clinical needs, and avoid reducing complex biomedical facts to terse slogans that obscure real-world variation ^{[5] [6]}.