3.3 Social Structures and Sex Differences

Sex differences linking hormones and behavior are often explained by the increased production of androgens (male sex hormones) by embryonic testes (male reproductive organs) in comparison to embryonic ovaries (female reproductive organs). It is hypothesized and supported by some evidence that these differences contribute to developments in the body, central nervous system, and behavior that are respectively either traditionally masculine or traditionally feminine. Generally, elevated levels of androgens are associated with aggressive, traditionally masculine behaviors (Batrinos, 2012), while traditionally feminine behaviors are sometimes attributed to a lack of androgens. It is also argued, based on findings in animal models, that sex differences can be attributed to differences in early brain organization that interact with both hormonal differences and socialization differences throughout the lifespan.

However, human models attempting to explain sex differences are marred with bias, particularly due to the underrepresentation of females in neuroscience brain research and the underrepresentation of people identifying as transgender (i.e., people whose gender identity does not match their sex assigned at birth based on observable external genitalia). Additionally, average sex differences in the behavior of girls and boys, such as girls’ nurturing behavior and verbal skills and boys’ aggressive behavior and visuospatial abilities, are small and can be attributed to gender stereotypes and societal expectations for girls and boys (Mesman & Groeneveld, 2018; Mondschein et al., 2000). Gender stereotypes permeate societies, molding societal expectations about gender roles. Parental expectations about their children’s abilities are a good example of this. Gendered parenting begins in infancy in parents’ choices of clothes and toys (Mesman & Groeneveld, 2018) as well as in their expectations about their child’s abilities. For example, studies have shown that mothers underestimate their daughters’ motor abilities and overestimate their sons’ motor abilities (Mondschein et al., 2000). Parental expectations, in turn, affect children’s respective performance in these areas (Hildenbrand et al., 2023).

Caution should therefore be taken not to interpret sex differences in neuroscience as fixed, given what is known about neuroplasticity (i.e., the ability of the brain to change due to experience) and the role of human experiences in shaping brain development (Friedrichs & Kellmeyer, 2022). For people who have been diagnosed with differences in sex development (DSD) and have been exposed to high levels of androgens in utero, which are associated with traditionally masculine behaviors, gender of rearing (i.e., the gender in which they were socialized) is the strongest predictor of gender identity in adolescence and adulthood (Callens et al., 2016). This suggests that the gender in which children are socialized or reared has a stronger effect on their gender identity later in life than their sex chromosomes do.

Environmental factors, such as stressors, impact the level of hormone production, which can have differential effects on females versus males (Lee et al., 2024). People from various social groups, such as Black girls, face the compounding effects of gender and racial discrimination. These experiences can contribute to increased levels of stress-related hormones and impact the level of internalizing and externalizing behaviors in BIPOC boys and girls (Assari et al., 2020; Lee et al., 2022; White et al., 2013).