Gender identity is defined as a person's perception of having a particular gender, which may or may not correspond with their birth sex.  Many biologists argue that our gender is biologically determined – that is, it is the result of sex hormones.  Kohlberg argued that our gender identity is linked to our cognitive development. Social psychologists argue that our gender identity is the result of socialization - that is, we learn our gender identity by interacting with adults and peers. The limitation of these traditional arguments is that they do not explain non-binary and transgender identity.

Biologists have typically had a deterministic argument – that our biology is our destiny. This is based on both genetics and sex hormones.  The theory of psychosexual differentiation argues that prenatal exposure to hormones is the most important factor in the development of gender identity and socialization plays a secondary role.  Research by Gorski injected testosterone into female rats while still in the womb.  The researcher found that in adulthood, these female rats mounted other female rats. It appears that higher levels of testosterone had a key effect on gender behaviour.  However, this study is limited because it is done on animals.  It is difficult to argue that “gender identity” in humans has an equivalent in rats. In addition, it appears that Gorski’s research lacks construct validity – assuming that sexual behaviour is an indication of gender identity.

Imperato carried out a case study on a family that had a genetic mutation where the children were as girls but then, during puberty, developed into boys. The genetic mutation is due to a lack of testosterone in the womb so that the penis did not descend until testosterone increased in puberty.  Although these children were raised as girls, after puberty they were masculine, heterosexuals.  When interviewed, they said that they were never happy “being a girl.”  Although this research is interesting, it has a few problems.  First, it is a rather extreme case and does not represent the experience of most people in their gender identity development.  In addition, the interviews have the problem of asking people how they felt about their gender identity as a child.  This is open to demand characteristics – as well as memory distortion.  It is difficult to confidently conclude that they were “always” aware that something was not right. The children may feel that this is what the researcher was expecting them to say.

Kohlberg argues that gender identity develops hand in hand with our cognitive development.  He argued that there are three stages of gender identity development. First, there is gender labeling, where a child identifies gender based on physical appearance – the way one dresses or the length of their hair.  Then around age 4, they show gender stability, where they realize that they will not become the other gender, but see that one’s behaviour is what identifies someone has a boy or girl.  The final stage, around age 7, is when a child recognizes that gender is constant across time and regardless of the situation.

To support his theory, Kohlberg carried out a series of interviews with children. In his interviews, he asked questions such as “who takes care of the babies?” or “who goes to work?”  He also asked if a boy can wear girls’ clothes.  There are many criticisms of these interviews.  The questions were “forced choice,” so the children did not answer “they both go to work.” This may also reflect the children’s cognitive and linguistic skills, rather than their understanding of gender.  In addition, more modern research shows that children are aware of their gender identity much earlier than Kohlberg thought. Toy preference has been shown as early as two-years-old. It may be that socializing factors play a significant role much earlier than previously believed.

It is difficult to separate gender identity from gender roles.  Social psychologists argue that our gender identity is the role of socialization – that is, we learn our gender role that matches our sex and this gives us our gender identity.  These concepts are not 100% distinct from one another.  Once a child realizes that he is a boy or she is a girl, they then develop a social identity, seeing their out-group as having a homogenous set of traits.  These traits are often seen as less desirable. When young girls are asked about traits of young boys, they often say they are “loud, aggressive, don’t play fair,” and boys say that girls are “weak, boring, etc.”  

The research on gender identity is complex.  It is not possible to isolate biological factors or sociocultural factors. Arguing that gender identity is solely based on our sex hormones is not only reductionist, it does not explain differences in gender identity. This is also true of cognitive and social arguments.  If children are enculturated into their gender identity, then why are boys raised by single moms not more feminine? Or why do some children grow up to be transgender, in spite of being raised by both parents?  Although there are theories regarding both potential biological origins of transgender behaviour – as well as the theory that the child may have been rewarded for gender non-conforming behaviour and punished for gender-conforming behaviour, there is a lack of research to support these claims. It may be that we have a theory for why the majority of people have a gender identity that matches their sex, but we do not have a theory that explains the wide range of human behaviour and why some children do not conform to society’s expectations.