Biological explanations of gender development argue that inherited chromosomal patterns and hormone exposure, especially before birth and during puberty, contribute to later gender identity and gender-typed behavior.

Chromosomes as a starting point

In biological explanations, chromosomes matter because they carry the genes that guide early development and influence later hormone production.

Humans usually have 23 pairs of chromosomes.

This karyotype diagram shows the 22 pairs of autosomes plus the sex chromosomes, with an inset comparing XX and XY. It helps you visualize how the 23rd pair differs between typical female (XX) and typical male (XY) chromosomal patterns—an important starting point for biological explanations of gender development. Source

The 23rd pair is most relevant here: XX is usually linked with female development and XY with male development. In typical development, a gene on the Y chromosome, often called SRY, triggers the formation of testes. These testes then produce androgens such as testosterone. When this pathway is absent, ovaries usually develop instead, and the hormonal environment is different.

This means chromosomes do not directly create masculine or feminine behavior. Instead, they begin a developmental sequence in which genes affect gonads, gonads affect hormones, and hormones affect the body and brain.

Key chromosomal pathway

• XY pattern: Y chromosome present, SRY activated, testes develop, prenatal androgen exposure is usually higher.

• XX pattern: No Y chromosome, ovaries usually develop, prenatal androgen exposure is usually lower.

• These different hormone patterns may bias later gender development, including activity preferences, play styles, and aspects of identity.

• Chromosomal influences are usually described as indirect, because they operate largely through hormones.

Hormones and the developing brain

In this topic, hormones are important because they are chemical messengers that can shape development before birth and again at puberty.

Researchers are especially interested in prenatal hormones, because exposure during early development can have lasting effects. Higher levels of prenatal testosterone are linked in some studies with more traditionally male-typed behavior, such as higher activity levels or greater interest in rough-and-tumble play. Lower androgen exposure, or reduced response to it, is linked with more typically female patterns. Estrogen also contributes to development, but many biological explanations emphasize the role of testosterone and other androgens in masculinizing the fetus.

These effects are not simply short-term. Early hormone exposure is often described as having an organizational influence on the nervous system.

By contrast, hormones released at puberty can have activational effects, meaning they trigger or strengthen tendencies organized earlier.

The figure on this page (Figure 11.13) plots typical developmental patterns of gonadal steroid hormones across early life and puberty (e.g., an early-life testosterone surge in males and rising gonadal hormones at puberty). It supports the organizational–activational distinction by visually separating early sensitive-period exposure from later pubertal increases that tend to activate or amplify previously organized systems. Source

Puberty matters for gender development because rising hormone levels coincide with major physical changes and may intensify certain behavior patterns, interests, and self-perceptions.

Biological theorists therefore argue that the same hormone can have different effects depending on when it is released. A high level of testosterone during a sensitive prenatal period may help organize neural systems, whereas similar levels later may mainly activate behavior already shaped earlier. This is why timing, receptor sensitivity, and duration of exposure are all important.

Prenatal and pubertal influences

• Prenatal hormones help organize parts of the brain linked with behavior and emotional responding.

• Testosterone is often highlighted because higher prenatal exposure is associated with more male-typical development.

• Estrogen becomes especially important in pubertal development and can contribute to female-typical physical and psychological changes.

• The timing of hormone exposure matters, not just the amount.

What biological explanations try to explain

Biological accounts are useful because some aspects of gendered behavior appear very early in life. Children may show consistent preferences for certain toys, activities, or play styles before they fully understand cultural expectations. A chromosome-and-hormone explanation suggests that part of this pattern may come from biological predispositions, not only imitation or reinforcement.

Some theorists also argue that hormone exposure may influence later gender identity, meaning a person’s internal sense of their gender. However, evidence for identity is less direct than evidence for gender-typed behavior, so claims should be made cautiously.

A key exam point is that biological explanations usually describe probabilities, not fixed outcomes. People with similar chromosomal patterns can still differ greatly in identity, interests, and behavior. This is partly because genes and hormones operate in complex ways, and individuals may vary in how sensitive they are to the same hormone levels.

Strengths and limitations of chromosome-and-hormone explanations

Strengths

• They provide a clear mechanism: chromosomal differences influence gonadal development, which changes hormone exposure, which can affect the brain and later behavior.

• They help explain why some gender differences appear early, before children have had extensive opportunity to learn social rules.

• They are supported by research suggesting links between prenatal androgen exposure and later gender-typed preferences.

Limitations

• Biological explanations can become too deterministic if they suggest chromosomes or hormones fully control gender development.

• Human evidence is often correlational, so it can be hard to prove that hormones directly caused a later behavior.

• Measuring prenatal hormones accurately is difficult, which limits certainty.

• Similar biology does not always produce the same outcome, showing that chromosomes and hormones are important influences, but not complete explanations.

• Brain development remains plastic, so biological influences can be modified by later experiences.