CHROMOSOMES AND HORMONES IN SEX AND GENDER

overview

biological sex is determined by genes

each pair of chromosomes carry genes that control different characteristics

biopsychologists assume that gender identity arises from biological processes, as a result of how their brain works

humans have 23 pairs of chromosomes - one pair determines an individuals sex

males and females differ in their sex chromosomes

females have XX, males have XY

development - testosterone

in male embryos, the SRY gene on the Y chromosome causes the gonad to develop into testes, which then secrete testosterone, when foetus is around 3 months old

testosterone stimulates the development of the male sex organs, but also cause the male brain to develop differently from the female brain

during prenatal development all individuals start out the same - external genitalia that look feminine

testes/ovaries therefore strongly influence gender development, through the effects of hormones

there is usually a direct link between individuals chromosomal sex, their internal genitalia (ovaries or testes) and external genitalia (vagina or penis)

reiner and gearhart 2004

studied a sample of 14 children born with cloacal exstrophy -birth defect, many abdominal organs are exposed, splitting both male and female genitalia

provided some insight into what can happen when genetically male children are sexually reassigned female and raised as girls

they were reassigned female at birth (born genetically male)

findings: 8/14 identified themselves as boys

all of the participants had at least male typical attitudes and interests

provides some support for the argument that biological variables have an impact on gender identity and behaviour

hormones

eg exposure to high levels of testosterone before birth, may lead to a more masculinised brain and behaviour

testosterone (androgen) affects typically males behaviours such as dominance or aggression

males and females produce different sex hormones in varying quantities which have an effect on behaviour

testosterone stimulates the development of male secondary sex characteristics that emerge at puberty

money and ehrhardt 1972

the girls exhibited male type behaviours eg playing energetic sports, and an absence of female type behaviours eg. playing with dolls

this suggests that testosterone has a strong influence on gender behaviour

reported on a sample of girls whose mothers took drugs containing testosterone during pregnancy

testosterone and brain development

such as areas linked to spatial skills and behaviours like aggression and competitiveness

the sexually dimorphic nucleus SDN is larger in males

testosterone is thought to act on the hypothalamus, without this the brain develops as a female

oestrogen

oestrogen has psychological and behavioural effects, such as premenstrual tension PMT, which is associated with emotionality and irritability

oestrogen feminises the brain, promoting neural interconnections for a more distributed, bilateral brain

promotes the development and maintenance of female characteristics and regulates menstruation

fitch and deneberg

this led to changes in the corpus callosum area and therefore affected connectivity between hemispheres

this supports the idea that oestrogen is involved in the feminisation of the brain

suppressed production of oestrogen by removing ovaries from female rats

oxytocin

oxytocin affects female social behaviour such as mate selection, pair boding, monogamy

the love hormone produced in both males and females - helps facilitate childbirth

strength

for example, in all cultures studied, men are found to be more aggressive than women

this suggests that male traits, such as aggression, are biologically determined through exposure to testosterone

the biological view of gender is supported by cross cultural studies that have found universal features of gender

weakness

research carried out with non human animals there is a need for caution in assuming that the results apply to humans

the physiology of humans and animals, like rats and mice, especially in terms of brain functioning is very different and human development and behaviour are much more subject to social and cultural influences

extrapolation issues

only provides limited support for the idea that hormones influence our behaviour