Psychologists deal with a broad array of populations and must take into account differences in population characteristics when making predictions about behavior. If certain such characteristics are used inappropriately in making judgments, however, prejudice can result, and acting on prejudicial judgments leads to such discriminations as sexism, racism, and ageism. Psychologists are working to identify and hope to eliminate the bases for making inappropriate judgments concerning gender, cultural, racial, and age differences.

While in conversational English the term gender has come to refer to the biological characteristic of being female or male, in psychology, the term refers more inclusively to the social and cultural dimensions of being one sex or the other. Gender identity concerns individuals' perception of themselves as and identification with being female or male. A Gender role is the set of societal expectations that dictates how an individual of a gender should behave, think, and feel. During the past century, perception of all three aspects of gender have changed, particularly that of gender roles.

Biological factors. Although sex is determined by the presence of two X chromosomes or one X and one Y chromosome, early in development, male and female fetuses are similar. Testes of males begin to differentiate around the seventh week after conception and ovaries of females around the twelfth week. Testes begin to secrete testosterone, which influences the development of the male sex organs.

Cognitive factors

  • The cognitive development theory contends that because children consistently hear themselves called “boy” or “girl,” they begin to conceive of themselves as being of one sex or the other. Ultimately, from such interactions, children develop a conception of attitudes toward and behavioral expectations concerning that gender.

  • The gender schema theory concerns the development of an internal schema, or mental framework, which organizes and directs the behavior of an individual as a male or female. For example, the gender schema of being female might include the proposition “I am a girl, so I play with dolls, not trucks.”

Social factors. A society's treatment of one gender is often different from its treatment of the other, even from the time a child is born— for example “blue for boys and pink for girls.” Social learning theory contends that children learn to behave in ways they are expected to behave as male or female by observing and imitating behaviors of people of their gender.

Gender roles. In the process of social learning, a child begins to learn her or his appropriate gender role, the sum of the behaviors society expects of females and of males. Gender roles vary in different cultures and have changed with time. Only recently has the role of “mother” been associated with that of “breadwinner” as well as that of “homemaker and mother.” Although the term androgyny in popular usage often refers only to a combination of masculine and feminine physical characteristics, it is now frequently used specifically to describe an individual who displays both masculine and feminine characteristics of any kind that are deemed desirable, such as those shown by a man who engages in rough wrestling matches and yet tenderly holds and feeds a baby.

The psychology of gender. Courses on the psychology of women are now part of the curriculum at all major universities, and feminist scholars have reviewed the contributions made by women world‐wide. Concomitantly, prejudice toward and discrimination against females at all developmental stages and both past and present (such as evidenced by treatment in classrooms and differences in salary) have been identified with the hope of ending them. Women of lower socio‐economic status and of ethnic backgrounds different from that of the majority (in the United States, especially black women) have been particularly oppressed. Courses on the psychology of gender examine the role of gender in human behavior and the development of attitudes.