There is no single number that answers this question, because “gender” is not one thing with one definition. Biological sex in humans is largely organized around two reproductive roles, but gender, as researchers and clinicians use the term, refers to a broader set of identities, roles, and social expectations that different cultures have organized in different ways across history. Some societies formally recognize two genders; others have long recognized three, four, or five. Contemporary psychology and medicine increasingly treat gender identity as a spectrum rather than a fixed set of categories, which makes counting genders a bit like counting colors: the underlying reality is continuous, and how many labels you apply depends on the system you are using.
Why Sex and Gender Are Not the Same Question
Much of the confusion around “how many genders” comes from treating sex and gender as interchangeable words. In biomedical research, sex usually refers to biological characteristics like chromosomes, hormones, and reproductive anatomy, while gender refers to the socially constructed roles, norms, and identities that a person inhabits.1PubMed Central. Differentiating sex and gender in health research to achieve gender equity Sex in mammals is largely binary and rooted in genetics and physiology. Gender, on the other hand, can span a wide range of expressions and is often, but not always, aligned with a person’s sex.2PubMed Central. Do Sex and Gender Have Separate Identities?
This distinction matters because answering “how many sexes are there?” and “how many genders are there?” lead to very different kinds of evidence. Asking about sex takes you into genetics and developmental biology. Asking about gender takes you into psychology, anthropology, neuroscience, and culture. Neither question has a trivially simple answer, but they are different questions.
What Biology Shows About Sex
In mammals, sex determination begins with the differentiation of an initially undifferentiated gonad into either testes or ovaries. A gene on the Y chromosome called SRY acts as the master switch. When SRY is present and functional, it triggers a cascade of other genes, including SOX9, that push the developing gonad toward becoming a testis. In the absence of SRY, a parallel set of genetic pathways involving genes like RSPO1, Wnt4, and Foxl2 steer development toward ovarian tissue.3PubMed. Sry and SoxE genes: How they participate in mammalian sex determination and gonadal development? These male-pathway and female-pathway gene networks actively oppose each other, and this mutual antagonism continues throughout life to maintain the sex of the gonad.
This system is robust, but it is not a simple on-off switch. A large number of genes interact in the process, and imbalances or mutations in any of them can produce variations in sex development.4Endocrine Reviews. The Molecular Action and Regulation of the Testis-Determining Factors, SRY (Sex-Determining Region on the Y Chromosome) and SOX9 People with differences of sex development (sometimes called intersex conditions) may have chromosomes, hormones, or anatomy that do not fit neatly into the typical male or female categories. These variations are not common, but they are not vanishingly rare either. They illustrate that even at the level of biology, sex is better described as strongly bimodal rather than as two perfectly separated categories with nothing in between.
Gender Categories Across Cultures
If biology shows that sex is mostly, but not perfectly, binary, anthropology shows that cultures have drawn the map of gender in a variety of ways. Many Indigenous North American nations recognized people who occupied roles outside the male-female binary long before European contact. The modern umbrella term “Two-Spirit,” adopted in 1990, describes Indigenous people who are diverse in sexual orientation and gender identity, though the specific roles and definitions vary from nation to nation.5PubMed. Two-Spirit Identity in a Time of Gender Fluidity Some communities use older, language-specific terms like nádleehí (Navajo) or agokwe (Ojibwe). These identities have existed, as one study puts it, “since time immemorial,” and they carried recognized social and spiritual roles within their communities.6PubMed. Two-Spirit Identity and Indigenous Conceptualization of Gender and Sexuality: Implications for Nursing Practice
In the Istmo Zapotec community of Oaxaca, Mexico, people assigned male at birth who adopt feminine roles and are attracted to men are recognized as muxes, a culturally established third gender with roots predating Spanish colonization.7PubMed. A Retrospective Study of Childhood Sex-Typed Behavior in Istmo Zapotec Men, Women, and Muxes Research in the town of Juchitán finds that muxe individuals report being valued, respected, and supported in their families and communities, and that this cultural acceptance has positive effects on their health and wellbeing, even though they also experience some discrimination.8PubMed Central. Learning from gender-diverse thriving among third-gender people in Juchitán, Mexico
In Samoa, fa’afafine are people assigned male at birth who embody both masculine and feminine traits and hold a recognized social role. Fa’afafine report elevated willingness to invest in the care of nieces and nephews compared to both men and women, a behavior pattern that has drawn the interest of evolutionary researchers.9PubMed. (Trans)Gender Role Expectations and Child Care in Samoa Meanwhile, the Bugis people of South Sulawesi, Indonesia, have traditionally recognized five gender categories. Among them, the Bissu are considered guardians of social harmony and intermediaries between the human and spiritual worlds.10Proceedings.Icesy. The Presentation of BISSU as the Fifth Gender and Their Tolerance in the Social Space within the Bugis Community South Asia’s hijra communities represent yet another longstanding tradition of gender diversity.
The pattern that emerges is that a strict male-female binary is one way of organizing gender but not the only way, and not even the most historically common way when you look globally. Colonization played a direct role in suppressing many of these systems. As one study notes, some settler governments are now adopting multi-gender frameworks that are “reminiscent of the Indigenous systems they aimed to erase through colonial systems and practices.”11PubMed. Two-Spirit Identity in a Time of Gender Fluidity
What Brain Research Suggests
A separate line of evidence comes from neuroimaging. Researchers have compared brain anatomy and connectivity patterns across cisgender and transgender individuals, and the findings are consistent enough to be worth noting, even if they do not settle the question of how many genders exist.
One study of transgender women found that their brain anatomy fell between that of cisgender men and cisgender women, shifted in the direction of their gender identity rather than their sex assigned at birth.12PubMed Central. Brain Sex in Transgender Women Is Shifted towards Gender Identity Another study using functional brain imaging found that brain connectivity patterns differed meaningfully among cisgender men, cisgender women, transgender men, and transgender women, with some measures showing transgender women and cisgender women clustering together while cisgender men formed a distinct group.13PubMed. Brain network interactions in transgender individuals with gender incongruence Work measuring whole-brain dynamics has also found significant differences across all gender groups, suggesting that gender identity has detectable neural correlates.14PubMed Central. Whole‐brain dynamics differentiate among cisgender and transgender individuals
These findings do not prove that gender identity is “hardwired” in a fixed number of brain types. Brains are extraordinarily variable, and the observed group differences are statistical trends, not diagnostic markers. But the research does suggest that gender identity is not simply a social preference; it has roots in the body’s biology. The brain does not appear to come in just two gender-labeled versions.
How Prenatal Hormones Shape Gender Development
One mechanism that helps explain the brain findings involves hormones during fetal development. Testosterone exposure before birth influences a range of behaviors that differ between sexes, including play behavior, aggression, sexual orientation, and, critically, gender identity itself.15PubMed. Gender development and the human brain People who were exposed to atypical concentrations of androgens prenatally, whether because of genetic conditions or because their mothers received certain hormones during pregnancy, consistently show shifts in gender-related behavior and, in some cases, in gender identity.16PubMed Central. Early androgen exposure and human gender development
This does not mean that hormones alone determine gender identity in a simple dose-response way. Most people exposed to atypical hormones still identify with their assigned gender. But the fact that prenatal hormone variation can shift gender identity at all tells us something important: the biological inputs to gender are continuous and variable, not binary. Different people end up at different places on these biological gradients, and what we call “gender identity” emerges from a complex interaction between those biological starting conditions and the social environment a person grows up in.
Children and the Development of Gender Identity
Children begin distinguishing between gender categories early in life, recognizing gender labels and absorbing stereotypes within the first few years. Research on ordinary schoolchildren finds that gender identity is shaped by a mix of cognitive, emotional, social, and psychological processes, all of which influence how a child comes to see themselves and how that self-concept affects their adjustment.17International Journal of Behavioral Development. Gender identity in childhood: A review of the literature For most children, the sense of being a boy or a girl crystallizes by age three or four and remains stable.
For a smaller number of children, the experience is different. Some children consistently identify with a gender other than the one they were assigned, and some do not feel comfortable in either binary category. The World Health Organization’s work on the ICD-11 classification moved gender incongruence out of the mental and behavioral disorders chapter, reflecting a shift in how the clinical world understands gender diversity: as a natural variation rather than a pathology.18The Lancet Psychiatry. Gender incongruence of childhood: a developmental perspective on DSM-5 and ICD-11
Generational Shifts in Reported Gender Diversity
Survey data and clinical observations show that younger generations report more varied gender identities than older ones. Research on transgender populations has found that baby boomers and Generation X members are more likely to identify as trans women, whereas younger cohorts show greater diversity in how they describe their gender, including nonbinary and other labels that fall outside the traditional binary.19PubMed Central. Gender Variations, Generational Effects, and Mental Health of Transgender People in Relation to Timing and Status of Gender Identity Milestones
This raises an obvious question: are there actually more gender-diverse people now, or are more people feeling safe enough to identify openly? Probably both, though researchers lean heavily toward the latter explanation. The underlying distribution of gender identities may not have changed dramatically, but the cultural vocabulary and social permission to describe non-binary experiences have expanded enormously in the past two decades. When the only available categories are “man” and “woman,” people whose experience does not quite fit either one have no language for it. When additional categories exist and are treated as legitimate, more people recognize themselves in them.
Why Recognition Affects Health
The question of “how many genders are there” might seem abstract, but it has concrete consequences for people’s health and wellbeing. Research comparing cisgender and nonbinary individuals with bisexual orientation found that nonbinary people reported lower social support and worse psychological wellbeing than their cisgender peers, but higher identity affirmation, suggesting they had a clear internal sense of who they were even when the social environment was not supportive.20PubMed Central. Social Support, Identity Affirmation, and Psychological Well-Being: A Developmental and Intersectional Comparison between Italian Cisgender and Non-Binary People with Bisexual Orientation
In mental health care specifically, transgender and nonbinary adults who receive gender-affirming therapy report greater satisfaction and better outcomes, while the most common reason for dropping out of therapy is a lack of practitioner understanding, not the resolution of their problems.21Sexuality Research and Social Policy. Mental Health Care for Transgender and Non-binary Adults: An Investigation of Affirmative Practice, Therapy Experiences and Outcomes, and Reasons for Treatment Termination Only about one in five people who stopped therapy did so because their issues had actually been resolved. The rest left because they felt misunderstood.
The cross-cultural evidence reinforces this. In communities like the Istmo Zapotec, where muxes hold an accepted social role and are valued by their families, gender-diverse people report notably better wellbeing than gender-diverse people in cultures that lack such frameworks.22PubMed Central. Learning from gender-diverse thriving among third-gender people in Juchitán, Mexico The number of gender categories a society recognizes is not just a classification debate; it shapes how people are treated and whether they thrive.
How Language Itself Shapes Gender Perception
One underappreciated factor in the “how many genders” question is the role of language. Languages structure gender in very different ways. Some, like French and Spanish, assign grammatical gender to every noun. Others, like English, largely restrict grammatical gender to pronouns. Research on French-English bilinguals has found that grammatical gender automatically influences how people perceive and categorize the world around them, even affecting their snap judgments about whether faces look masculine or feminine.23PubMed. Grammatical gender affects gender perception: Evidence for the structural-feedback hypothesis
This finding suggests that the language you speak does not just reflect how you think about gender; it actively shapes it. A person raised in a language and culture with two firmly grammatical genders may literally perceive gender differently than someone raised in a language without grammatical gender or in a culture with multiple recognized gender roles. This does not mean language determines gender identity, but it does mean that the categories available to us influence how naturally we perceive variation. When you only have two buckets, everything gets sorted into two buckets, even when some of the contents do not fit either one particularly well.
Behavioral Diversity Within Sex in the Animal Kingdom
Looking beyond humans, the picture gets even more complicated. In many animal species, individuals of the same sex adopt strikingly different reproductive strategies. Males in a single population may develop into distinct physical and behavioral types, with some using aggressive competition to attract mates and others using stealth, mimicry, or cooperative strategies. These alternative reproductive tactics can be genetically encoded, shaped by environmental conditions during development, or some mix of both.24PubMed. Male alternative reproductive tactics
Nobody would call these “genders” in the human cultural sense. But they complicate any claim that nature neatly sorts organisms into exactly two behavioral categories per species. Biological sex may be organized around two reproductive functions, but the behavioral and physical expression of sex shows enormous variation even in species with no culture, no language, and no politics. The diversity that humans show in gender identity and expression is, in a sense, a more elaborate version of a pattern visible across the animal world: the same underlying biological variables producing a range of outcomes, not just two.