Gender and Biological Sex

Biological sex and gender are often presented side by side in today’s debate as though they were two equivalent, independent dimensions of a person. That view is philosophically and scientifically contested. Biological sex is a factual, biologically grounded category; “gender” is a theoretical concept introduced in the second half of the twentieth century to describe social roles and subjective experience. The relationship between the two is far less straightforward than is often suggested.

What is biological sex?

Biological sex in humans — and in all mammals — is binary. It is defined by the type of gamete an organism produces or would produce: small, motile gametes (sperm) in males, and large, non-motile gametes (eggs) in females. There are only these two gamete systems; no third reproductive category exists in human biology. Sex is observed at birth, not “assigned”: doctors and parents observe what is anatomically visible, and in almost all cases they are immediately correct. The origin of the phrase “assigned at birth” is explained on letterbrij.nl.

Intersex conditions (disorders of sex development, DSD) are medical conditions in which the development of sex characteristics proceeds atypically. They occur in approximately 0.018% of the population when only clinically apparent cases are counted. Even in DSD, there is almost always an underlying male or female gamete system; intersex is not a “third sex”. Activist literature that uses DSD as evidence for a sex spectrum (often citing figures of up to 1.7%) relies on a broad definition proposed by Anne Fausto-Sterling, which has been refuted by physicians such as Leonard Sax as methodologically unsound.

What is gender?

The word “gender” was introduced into science in the 1950s by psychologist John Money to describe the social role aspects of sex. Since then, the concept has been expanded considerably: from “social role” to “inner identity.” The World Health Organization now uses a formulation in which gender encompasses an inner, personal experience. This is a remarkable expansion, because an inner experience is by definition not objectively measurable. Unlike biological sex — which can be demonstrated in cells, hormones, and anatomy — “gender identity” rests solely on self-reporting.

This difference is fundamental. Presenting the two concepts as similar properties of a human being suggests that a feeling has the same ontological status as a bodily reality. That is a philosophical choice, not a scientific finding.

The distinction in science and practice

In medicine, biological sex is an indispensable variable: it affects how medications work, the course of diseases, screening recommendations, and surgical procedures. Gender — in the sense of social role — can be an additional variable (men, for example, are less likely to seek help), but it does not replace sex. Recent criticism from authors in The Lancet and BMJ, among others, points out that replacing “sex” with “gender” in medical data and forms leads to information loss and patient-safety risks.

The claim that biological sex is also “a spectrum” is sometimes put forward, but it is broadly rejected by evolutionary biologists. The definition of biological sex is a recurring topic on Reality’s Last Stand, the publication of evolutionary biologist Colin Wright. Variation within the sexes (tall women, short men, hormonal outliers) is not the same as a spectrum between the sexes. The binary sex structure is one of the most conserved features in the evolution of sexually reproducing species.

Political and social debate

The question of what should take precedence legally — biological sex or self-selected gender — has concrete consequences for sport, prisons, women’s shelters, medical statistics, and the collection of population data. The shift from sex to gender in official records rests on the assumption that self-identification, without further verification, is sufficient. Critics, including many feminist authors, point out that this undermines sex-based rights to separate facilities — a right that women fought hard to secure in the twentieth century.

In countries such as the United Kingdom, Sweden, Finland, and Norway, there has been a move away in recent years from a purely self-identification-based approach, following reports such as the Cass Review and Sweden’s SBU report. See also detransition and rapid-onset gender dysphoria for related discussions.