The role of chromosomes and hormones in sex and gender

• Chromosomes are 46 (23 pairs) of biological threads of DNA found inside the nucleus of cells
• Studies on testosterone

  • Albert et al (1989) found injecting female rats with testosterone made them act more aggressively
  • Dabbs et al (1995) studied a prison population, finding prisoners with higher testosterone levels were more likely to have committed violent crimes
• Hormones

  Biochemical messengers released from glands into the bloodstream to influence the functioning of other bodily organs and systems
• Genetic differences between male and female chromosomes

  Result in observable behavioural variations by coding for different neuronal structures and hormone levels that influence gender expression
• Genetic differences between biologically male and female chromosomes are thought to result in observable behavioural variations
• The 23rd chromosome pair determines the biological sex of a person
• Testosterone's role in gender


  After birth, associated with stereotypical male behaviours such as aggression and competitiveness
• Testosterone's role in sex

  Causes physical changes such as the development of male sex organs and psychological changes because prenatal testosterone causes masculinisation of the brain
• Testosterone's role in sex

  Stimulates the development of the male foetus as genes in the Y chromosome cause testes to form and produce androgens, resulting in other sex differences
• Testosterone is the primary androgen. Men have 10x more testosterone than females
• Oestrogen is a female sex hormone, in much higher concentration in females
• Oestrogen's role in sex

  Regulation of the menstural cycle and development of secondary sexual characteristics
• Testosterone's role in gender

  Linked to higher levels of aggression, a trait thought to be masculine in nature
• Oestrogen's role in sex

  In the womb, having an X chromosome means ovaries form resulting in higher levels of oestrogen. These higher oestrogen levels have feminising effects on brain development
• Oestrogen's role in gender

  Associated with stereotypical female behaviours such as compassion and sensitivity
• Studies on oestrogen


  • Ardekani et al (2013) found women have more neural connections between the left and right hemispheres than men, resulting in more evenly distributed use of both brain hemispheres
• Oxytocin's role in gender

  Explains the caring/attachment behaviour in females. Typically characterised as fight or flight, Taylor et al (2000) found the female response to stress is better characterised as 'tend and befriend'. The researchers suggest these behavioural differences in response to stress are caused by differences in oxytocin activity between men and women
• Oxytocin is a hormone produced in a higher quantity in females (same amount in both sexes during intercourse)
• Oxytocin's role in sex

  Plays an important role in childbirth and stimulates lactation in females to enable breastfeeding and reduces the effect of the stress hormone cortisol
• Van Goozen et al (1995) demonstrated that administrating cross-sex hormones to transgender people results in gender-stereotypical behavioural changes. For example, FtMs given testosterone act more aggressively and MtFs given estrogen act less aggressively. 
• Atypical sex chromosome patterns- such as Klinefelters Syndrome and Turner’s Syndrome – demonstrate how chromosomes also have important effects on gender development.
• Some studies question the effects of hormones on gender-typical behaviour. For example, Tricker et al (1996) randomly assigned 43 men to receive either 600mg of testosterone per week or placebo but found no differences in aggression between the two groups.
• A potential negative consequence of biological explanations of gender development is that it could reinforce harmful stereotypes. For example, if males have a slight advantage in spatial reasoning on average, it might cause society to discriminate against women entering fields that require spatial reasoning (e.g. engineering) even if the woman is equally or more able than the average man.
• A lot of evidence for the role of hormones in gender development has methodological issues as it comes from animal studies and so the results might not apply to humans.