“Boy or girl?” is most often among the first questions asked about a person. The answer may precede your name. It precedes your earliest memory, and every thought you eventually form about yourself. Other people read your body, choose your pronouns, and begin to imagine who you will be long before they get to meet your personality. This first inherited account of yourself may be given so surely that it forgets to be examined. In reality, it may only partly fit, change its meaning over time, and leave many experiences unnamed. What may appear to be a simple fact paints a much larger portrait: the body you have, the place you occupy among others, and the person you recognize yourself to be.

Sex and gender gather several different things under one name. Chromosomes, gonads, hormones, anatomy, social expectations, and personal experience. All these contribute to your self in different ways and at different times. To understand how they become part of identity, we will separate these strands and follow each from its beginnings.

Let's recall the basics: sex and gender

Sex refers to a constellation of biological characteristics, including chromosomes, sex-determining genes, gonads, hormones, internal reproductive organs, external genitalia, and the secondary sex characteristics that emerge at puberty. Assigned sex is the category recorded at birth, usually according to the appearance of the external genitalia.

Gender emerges from the social and personal world that develops around sex. It includes the meanings a culture gives to being a woman, a man, or another gender; the ways you express yourself; and your own experience of who you are. Gender identity, gender expression, and sexual orientation describe different aspects of your self, although they may become closely associated in your life.

Sex is multidimensional, since a person’s chromosomes, gonads, hormones, and anatomy do not invariably convey identical information. Most people develop through one of two common pathways, and the different dimensions of sex correspond closely. However, variations occur at every stage.

The first strand: chromosomes at conception

At the beginning, before names, expectations, or nursery colors, you were a cell. The cell carried chromosomes inherited from your two parents. Most commonly, an embryo receives either two X chromosomes, usually written as 46,XX, or one X and one Y, written as 46,XY. These combinations establish fundamental conditions for the development that follows:

• The Y chromosome usually carries a gene called SRY, which contributes to the activation of the genetic network involved in testicular development. Its presence alone, however, does not determine every subsequent sex characteristic. Other genes must respond, gonads must develop, hormones must be produced, and the body must be capable of responding to them.
• Variations sometimes occur during the formation of egg or sperm cells or during early cell division. A person may have a single X chromosome, as in 45,X; an additional X, as in 47,XXY; or an additional Y, as in 47,XYY. Mosaic patterns are also possible, which means that different cells within the same body carry different chromosomal combinations.

These variations usually arise by chance, beyond either parent’s control. Their effects differ considerably. Some become apparent early, some affect puberty or fertility, and some remain undiscovered unless chromosome testing is performed for another reason.

So, chromosomes begin the sequence. The body that will eventually be seen, named, and interpreted, develops through several further stages.

Taking the human shape: early sexual development

Until approximately the sixth week of embryonic development, the gonads remain bipotential: they have the capacity to develop along an ovarian or testicular pathway. A coordinated network of genes gradually carries development in one direction. SRY commonly participates in activating the testicular pathway, while another set of genes supports ovarian development.

When testes develop, they begin to produce anti-Müllerian hormone and testosterone. Anti-Müllerian hormone influences the internal reproductive tract, while testosterone and its more potent derivative, dihydrotestosterone, contribute to the development of male-typical internal and external anatomy.

The penis and clitoris emerge from the same embryonic structure, known as the genital tubercle. The scrotum and labia also develop from shared precursors. Hormone production, timing, conversion, and receptor response all influence the forms these structures eventually take.

If testis-determining signals are absent or ineffective, ovarian development proceeds through its own active genetic pathway. The internal and external anatomy generally develops along the female-typical course. Sexual differentiation is so a sequence of interacting genetic and hormonal events, never a single instruction contained in one chromosome.

When development takes another route

Variation can enter this sequence at several points. A person may have a Y chromosome without a functioning SRY gene. The testes may produce an unusual amount of a hormone, or the body may convert that hormone differently. Hormone receptors may also respond partially or scarcely at all.

In complete androgen insensitivity syndrome, for example, a person has XY chromosomes and develops testes that produce androgens, while the body’s cells cannot respond to those androgens. The external genitalia consequently develop in a female-typical form. Anti-Müllerian hormone is still produced, so the internal reproductive anatomy differs from that of most people with female-typical external genitalia.

Development may also vary in an XX fetus exposed to unusually high androgen levels, as can occur in some forms of congenital adrenal hyperplasia. Depending on the timing and degree of exposure, the external genitalia may develop characteristics that do not fall neatly within the most common female or male forms.

Such characteristics may be described as intersex traits or differences or variations of sex development. Some are visible at birth; others become apparent during puberty, through fertility investigation, or by chance. Their medical significance also varies. Certain conditions require prompt care, while others have little effect on health.

These variations remind us that assigned sex usually reflects one visible part of a much larger developmental history and a much richer reality.

Another layer: the developing brain

Sex-related development also involves the nervous system. Sex chromosomes, genes, and gonadal hormones influence the developing brain before birth and continue to exert effects throughout childhood, puberty, and adulthood. Average sex differences are evident in some aspects of brain structure, function, and behavior, although the distributions overlap extensively and individuals cannot be divided into two uniform types of brains.

The clearest human evidence for the influence of prenatal androgens concerns certain sex-typed interests and behaviors, particularly childhood play. Girls exposed to unusually high androgen levels before birth, most often studied through congenital adrenal hyperplasia, show increased interest on average in activities culturally associated with boys. These findings concern group tendencies and leave substantial variation among individuals. A review of early androgen exposure and gender development shows the evidence for effects on gender identity itself considerably less direct.

We see that gender identity develops through a complex relationship among biological, cognitive, relational, and cultural influences. The contribution of each remains difficult to isolate, and no single chromosome, hormone level, childhood preference, or brain feature can reveal an individual’s gender identity. People with similar developmental conditions may arrive at different identities; people who share an identity may have very different biology and developmental histories.

Biology contributes to the conditions from which a self develops, and never defines the person’s first-person account in advance.

Puberty: the body becomes newly present

Puberty brings another period of pronounced hormonal activity. Rising androgen levels in a typical male puberty deepen the voice, promote facial and body hair, and alter muscle and fat distribution. In a typical female puberty, rising estrogen levels contribute to breast development, changes in body shape, and menstruation. Every body produces both androgens and estrogens, although their concentrations and patterns of secretion differ.

These changes make the body’s sex characteristics more visible and may give them a new personal and social significance. For some people, puberty brings an expected sense of continuity. For others, the developing body feels unfamiliar, unwelcome, or increasingly difficult to reconcile with their sense of themselves.

Puberty can bring an earlier question into sharper focus, introduce a question that had never arisen before, or pass with little reflection on gender. The meaning of the changes depends upon more than the hormones themselves; it also depends upon the person who encounters them and the social world in which they are interpreted.

How culture interprets the body

The social interpretation of sex begins remarkably early. Once a fetus has been described as a girl or a boy, other people may choose names, colors, clothes, toys, and imagined futures accordingly. After birth, differences appear in the language adults use, the behavior they encourage, and the qualities they notice or praise.

Children gradually learn the gendered meanings of the world around them. They observe who is expected to behave in which way, which possibilities appear available to them, and how departures from those expectations are received. They also participate in this process: they imitate, resist, reinterpret, and search for forms of recognition that make sense to them.

Culture supplies much of the vocabulary through which gender becomes intelligible. It shapes what femininity, masculinity, and gender variance can mean at a particular place and time. The same body, gesture, preference, or form of dress may carry different meanings in another family, community, or historical period.

Throughout development, biology and culture remain closely involved. Biological characteristics influence how other people respond to a child, while those responses influence how the child understands the characteristics. Neither process allows us to predict exactly what gender will come to mean to the person.

Development and social interpretation still leave one dimension unfinished: the meaning these descriptions acquire in your own experience.

When the description becomes personal

Other people encounter your sex and gender from the outside. They see a body, hear a name, use a pronoun, and place you within familiar social categories. Your acquaintance with these things follows another course. It includes how you experience your body, which forms of recognition feel natural, how you wish to appear among others, and whether the description you inherited seems to contain you adequately. For some people, these elements remain in such quiet agreement that gender rarely becomes an object of thought, and it belongs to the familiar background of the self. Others experience gender as a distinct and intimate certainty. Still others encounter it as a question whose meaning emerges only gradually.

The question may first appear through discomfort with a role, an unexpected ease in another form of expression, a private image that returns, or the peculiar intimacy of being addressed differently. You may notice that you feel more recognizable to yourselves in certain clothes, among particular people, or under another name. An apparently minor detail can reveal that a given description is missing something. These experiences do not invariably lead to one immediate conclusion. You may need time to distinguish your relationship with your body from your relationship with gendered expectations, expression, sexuality, belonging, or recognition. These parts can correspond closely or move along different routes.

Gender incongruence can exist without gender dysphoria, and many people examine their gender without seeking medical treatment. It’s a consequence of the complex interplay of biological, environmental, and cultural factors and does not invariably involve distress or treatment.

Self-acquaintance can precede any label or decision. It may bring a definite label, reveal a more complicated relationship with existing categories, or make the uncertainty itself more intelligible. And only inquiry about the experience uncovers what it really contains. Developmental science can tell us how bodies take shape and which influences are associated with certain patterns. Social history can tell us how categories and expectations arose. But the significance of those facts in one particular life becomes known only through the person’s experience of them.

TL;DR

Sex and gender develop over time through several related layers. Chromosomes establish some of the earliest biological conditions. Networks of genes guide gonadal development; hormones and receptors influence internal and external anatomy; the brain continues developing under genetic, hormonal, and environmental influences. Puberty makes many sex characteristics more pronounced. Culture gives these characteristics social meanings and places you within a field of labels, roles, expectations, and possibilities. Gender identity concerns your own experience within that field. Biology, culture, and personal history all contribute, while no single factor determines precisely who you become.

The question “boy or girl?” asks for a category that describes something only sometimes useful. But the answer remains of little significance besides the person who grows from it. The category can imperfectly record chromosomes, summarize only the visible anatomy, and establish a social position that leaves much of the self ill-defined. It may sometimes begin, but never finish the portrait. What you are, how you are experienced, questioned, revised, and made your own, unfolds through the continuing acquaintance between your environment, time, and your self.