Is sex binary? The answer to this question depends on who is asking, and why.

There is a classic taboo against discussing politics, religion, and money at polite social gatherings.  These days, one probably needs to add sex and gender to that list. 

(Sex and gender are not the same thing. My commentary here is limited to biological sex as a category and does not address the social construct called gender.)

Unless you are live entirely off the grid, you know that there is a fierce public debate about the definition of sex and what defines male versus female. This debate also exists in biological fields: evolutionary biology, developmental biology, physiology, genetics, reproductive biology, ethology, and others. The public debate tends to be acrimonious with judgmental religious, and moral commentary, ad hominem arguments, and even overt threats. The scientific debate is usually more academic, and respectful. The public and academic discussions both struggle for consensus because the human drive to define categories conflicts with the fact that Nature is category agnostic. 

I start with a discussion of categories, first in general, then as used in biologic sciences, and finally when used for social purposes. I close by (sort of) answering the question.

Generic

Categories (and labels) are universal and indispensable tools used by humans to survive. They simplify an infinitely complex reality to make it cognitively manageable. Imagine, instead of apple, having to say ‘roughly round, usually red on the outside and white on the inside, 2-3-inch diameter fruit that grows on trees, is usually sweet and crisp, and can be eaten fresh or baked in pies and other desserts! Categories provide a foundation for recognition, pattern finding, organization, prediction, memory, communication, reasoning, decision making, identity formation, and social cooperation and collaboration.  They promote cognitive efficiency, facilitate discovery, fairness, and consistency, and allows us to deal with intangible concepts and phenomena. 

Though necessary and effective, this simplification of massively complex realities into categories causes problems when we confuse our simplified (and therefore inaccurate and incomplete) category for the complex and nuanced reality it represents. Polish American scholar and philosopher Alfred Korzybski, founder of general semantics, termed this equating the map with the territory.) This ‘reification’ results in imagined boundaries that do not exist in reality, blindness to important variation within categories, essentialism (assuming every item in a category contains an innate essence that defines it), stereotyping, confirmation bias (interpreting information in a way to reinforce the existing category), and loss of information (discarding information and/or detail that does not fit or is not seen as essential to the category assignment). 

Every category is simultaneously useful and problematic to the extent that it discards or ignores information and detail. 

Asking these eight questions can help us use categories as tools without losing sight of the fact that they are simplified, incomplete, and inaccurate models of reality:

1. Who created this category, and why?
2. How is category membership defined? How many exceptions are there?
3. Are the category boundaries sharp or fuzzy, arbitrary or meaningful? 
4. How similar is this category to related categories?
5. How much variation is there within the category? Would a continuum work better than a category?
6. Is the category label descriptive or explanatory?
7. What problem(s) can the use of this category solve? What problems can it cause? To whom?
8. What new information might require changing or discarding the category?

Specialized uses of categories

Since the issue at hand is the categorization of sex into male and female, I will focus here on the field of biology. A similar analysis could be developed for any area of study. 

Reproductive biologists, who focus on sexual reproductive processes, use two binary categories of gametes produced parent organisms. For purposes of clarity, consistent definitions, and universally understood results, their work requires distinctly defined binary definitions of males and females producing ova and sperm. 

Evolutionary biologists focus on sexual differentiation, morphology, function, and behavior across wide geographic and chronologic contexts. Because evolutionary processes feature and depend upon variation and change, they need much broader and more inclusive categories for male and female, not constrained by the binary approached used by reproductive biologists. 

Developmental biologists focus on how sex evolves. Their scope ranges from broad (all living things), through subsets (animals, mammals, Homo sapiens), to very specific groups (in utero humans, adolescent humans). They need categories that allow them to focus on their specific area of study. 

Behavioral biologists (ethologists) focus on behavior. Their scope also ranges from broad (all animals) to specific subsets (mammals, adults, infants, cultures, an external variable like climate or nutrition). Their category definitions must reflect their specific needs. 

One could do a similar analysis for geneticists, physiologists, psychologists, pharmacologists, epidemiologists, toxicologists, or urologists. Each specialty will need and develop its own definitions and criteria for sex and sex-related groups. These categories will reflect the needs of those creating and using the categories: different maps emphasizing different aspects of the same territory. 

Societal applications of categories

How are categories of male versus female used in general society, by individuals and by groups? What purposes do they serve? 

Society needs categories to function effectively and efficiently. Categories allow organization of vast amounts of information, decision making, resource allocation, providing fair and consistent legal and public services, creating and managing markets, making communication, cooperation, and collaboration possible. In the broadest sense, the purpose of societal categories is to allow society to function. 

Individual subsets of society need and use their own categories to reflect and support the needs and functions of that subset. These needs and functions may or may not be identical to the needs and functions of other subsets, or of society taken as a whole. 

For example, musicians need categories related to specific instruments (piano, drum) or groups of instruments (brass, string), music genres (jazz, folk, Baroque), role (composer, performer, audience, teacher, critic, sponsor), or skill level (beginner, expert). 

Education may need music categories (learner, teacher, subject, instruments, band, orchestra), but they will not map reliably or consistently to the music categories important to musicians. Musical categories used by the military, businesses, or libraries will be similarly unique in both purpose and structure. 

Attempting to create a universally accurate and applicable system of categorization is, at best, a fool’s errand. At worst, it leads to discord, enmity and it undermines social cohesiveness. 

How does this apply to the current rancor over categories used to define male and female sexes in public life? The problem does not lie in the phenomenon being categorized. From the perspective of the Universe, biological sex manifests with amazing variety on a complex continuum, so there is no natural, universal demarcation that separates male from female. As individual humans and as sub-groups of humans with shared interests, we create categories and definitions that serve our needs as individuals or sub-groups. Problems arise when an individual or group wants to impose their categorical schema on another individual or group. The same problem would arise if developmental biologists tried to impose their schema on reproductive biologists. Scientists (mostly) agree to use each other’s categories when discussing work in the other’s domain and (mostly) refrain from attacking other disciplines or their members for being dishonest, immoral, or stupid. 

One can imagine a variety of approaches to societal categorization of male and female:

• Work within a specific scientific field. Reproductive biologists or anthropological biologists, for example. This works very well for them within their field but tends to be less functional when they generalize to society as a whole.
• Those using categories based on a religious, philosophical, or historical tradition. This includes those for whom some version of fairness or equity functions as their religion. Those who advocate for clear and concrete definitions of male and female tend to find ways to dismiss the impact on those who do not fit in their schema. Those who advocate for inclusive definitions tend to dismiss the impact of edge cases on the majority.
• Pragmatists who are willing to be flexible about definitions and criteria in search of a schema that satisfies either the most people or serves some important social function. They are often accused by everyone else of having weak (or no) principles.
• Minimalists who are not committed to a field, religion, or ideology and are not driven by pragmatism, but simply want to expend a minimum amount of time and selecting and defending a category. Their choice is one of convenience. It may reflect either the category used by their most salient social identity group, or by what they remember from the past, such as high school biology. 
• Bad faith actors exist in every aspect of life, and the issue of male versus female categories is no exception. There are people who pick a stance based on malevolence, some ulterior motive (to marginalize or harm some group), because they want attention, or because they simply like to argue. 

Most people operate from more than one of these approaches, related to different contexts (elementary school sports versus elite sports), different times (as they age, as their social context varies from work to church to home), or changed mindsets.

In closing… 

Returning to our original question ‘is sex binary?’ This cannot be answered without first exploring the question and its context. Even then, it is not a question with a right answer and a wrong answer. “It depends” is the best an honest person can do.

To have a productive conversation about the question, we need to reduce confusion, miscommunication, and polarization. The following questions can help:

1. What trait or traits are we measuring? Genes, gonads, gametes, genitals, hormones, body type, identity?
2. How is the trait distributed? A single discrete curve, one or more bimodal curves, more than one overlapping curve, a multidimensional (3D rather than 2D) curve?
3. What is the purpose of our categorization? Medical diagnosis or treatment, sociologic or evolutionary research, epidemiology, demographics, apportionment of services or resources, rules for belonging or participating, social identity or status?
4. What information does our schema minimize or discard in the interest of simplification and clarity?  
5. Who gains and who loses? What do they gain or lose? 

Answering these questions will not automatically produce a solution but can help transform an unresolvable dispute based on undefined terms and values into a resolvable dispute with defined terms and values.

Some further reading

"Sex is a Spectrum. The Biological Limits of the Binary" (2025) by Agustin Fuentes, American primatologist and biological anthropologist at Princeton University and formerly the chair of the Department of Anthropology at the University of Notre Dame.

"The Binary Delusion. How Biology Defies the Myth of Two Sexes" (2026) by Ari Berkowitz, Presidential Professor of Biology and Director of the Cellular & Behavioral Neurobiology Graduate Program at the University of Oklahoma.

"The Sexual Evolution. How 500 Million Years of Sex, Gender, and Mating Shape Modern Relationships (2025) by Nathan Lents, Professor of Biology at John Jay College (CUNY).

“Categories We Live By. How We Classify Everybody and Everything” (2024) by Gregory Murphy. Explores how our drive to categorize affects a broad range of individual and social experiences. Uses examples of real-world labels and shows that defining a category inescapably ignores or silences alternative perspectives.

“Sorting Things Out: Classification and its Consequences” (2000) by Geoffrey Bowker and Susan Leigh Star. Comprehensive discussion of the consequences of the invisible conceptual scaffolding underlying human classification systems. Explores how innate cognitive processes lead to social and bureaucratic rules and labels, and the impact they have on daily life.

“Natural Categories and Humans Kinds. Classification in the Natural and Social Sciences” (2015) by Muhammad Ali Khalidi. How classification and taxonomy are used in science. Discusses the contrasts between essentialism (categories exist in nature) and social constructionism (categories are created by humans).

“Women, Fire, and Dangerous Things. What Categories Reveal About the Human Mind” (1987) by George Lakoff. An old but classic linguistics text about how humans create, use, and are impacted by categories that are not natural but are metaphors, prototypes, heuristics, and models.

“It Could Have Been Otherwise. Science in the Age of Uncertainty” (2026) by Stuart Firestein. Treats answers and truths as provisional and often accurate in one context but not another. Advocates intellectual pluralism, the concept that many questions do not have only one answer but have many possible answers for different contexts or with different likelihoods.