The Role of Genes
Genes Sex is determined by which chromosomes present F=XX M= XY
- M inherit Y from father, X from mother. F inherit X from both. Thus sex of offspring entirely determined by which male sperm (X/Y) fertilises egg (X)
- Presence of Y chormosome that makes a person male, absence makes female
- SRY region on Y chromosome- fundamental role of sex determination. Believed to be switch that intiates the development of testes. Responsibe for initiation of male sex determination during embryo development.
Support/Criticism for role of genes
- Role of Y chromsome 1959> chromosomal analysis of 2 human disorders- TURNER & KLINEFELTERS syndrome
- - demonstrated for first time genetic factors on Y chromosome of mammals important in male sex. Through accidents of meosis during sperm& egg production, some people inherit XXY, but still male (Klinefelter). Others inherit 1 X, thus XO, but still female (Turner)
> REDUCTIONIST - argues genes only cause of sex determination; genes not enough to make male/female. Adequate level of tesosterone exposure needed during foetal development. If testosterone of cellular receptors for it lacking, like AIS, an XY human may be born with female genitilia & misidentified as baby girl. If XX fetus exposed to testosterone (from adrenal gland), may be misidetified as boy.
> FOXL2 challenges perception that gender determined purely by X/Y chromsome. Scientists identified gene that keeps females female.
Stops females developing male physical traits incl. testes & facial hair.
When artifically 'switched off' in adult female mice, ovaries began to turn into testes & started to produce level of test. found in male mice.
FOXL2= non-sex chromosome that is shared by males/females.
The Role of Hormones
HORMONES production of testosterone mediated by genes on Y chromosome
- Soon after conception, testes in male foetuses secrete testosterone at high rate. Also secreted by adrenal glands (explains why girls produce it). Boys before birth produce far more testosterone
- 3 stages in development for surges > Uterus - 8&24 weeks into pregnancy > around 5 months after birth > at puberty = ACTIVATIONAL PERIODS (at this time though brain most sensitive to hormonal changes)
- GESCHWIND speculated foetal testosterone affects growth rate of 2 hemispheres of brain. The + test. the faster right hemisphere develops, slower left.
- Now thought men demonstrate higher degree of hemispheric specialisation. Right hemisphere generally dominant in males, left females. Thought this may partially explain gender differences in spatial tasks (right) and language (left)
> ANIMAL STUDIES support for role of testosterone in male characterisitics.
Male rats find way through mazes quickly, fewer errors. Female rats injected with test. faster maze learning & fewer errors vs. females with no injections. TF & normal males appear to use directional strategy. Castrated males & NF use landmark strategy that can lead to errors. Such research allows IV manipulation in way not possible with humans; conclusions about Cause&Effect can be made. BUT, human gender identity different to that of rats. May be likely additional environmental factors influence humans & so may not be possible to generalise findings to humans.
> CORRELATIONAL STUDIES IN HUMANS Baron-Cohen studied babies whom mothers had undergone amniocentesis.
Analysed levels of test. present in fluid & then analysed toddlers at 12&24 months. + levels of test, less-eye contact & smaller vocab = LINK between test. & sociability/language ability. At aged 4, children with + prenatal test lower social skills & narrow interests. Pattern true for both genders. This study suggests a role of hormones in explaining variation within each sex aswell as between sexes. However correlation not causation & findings may be ungeneralisable as fluid taken as possibility of problem with child initially.
> ROLE OF TESTOSTERONE IN MALE CHARACTERISTICS study of girls with CAH (congenital adrenal hyperplasia) and David Reimer
CAH girls exposed to high testosterone pre-natally. EHRHARDT compared CAH girls to normal sister & found significant difference. CAH = high levels of energy expenditure, no interest in dolls but in cars, trucks, blocks. Showed little interest in future roles of brides/mothers but careers. Girls treated soon after birth so influence of test. before birth had long-lasting effects in development. Also, likely parents treat girls as girls so unlikely socialisation causes different behaviour- suggests nature rather than nurture.
David Reimer further supports. He suffered botched circumcision operation was reared as a girl. Alothough halied success for many years, David was unhappy as girl & converted back to male at 14 showing prenatal test. had influenced gender & nurture could not overcome nature.
> Biological explanation's alpha gender bias as exaggerates differences between sexes therefore socially sensitive. The danger with proposing biological theories of gender differences is it may be percieved as suggesting person is limited by their biology. Some argue it provides evidence that biology causes such difference to defend existing inequalities between sexes & goes against progress made in last few decades in terms of equal oppertunities for women. However Baron-Cohen points out evidence is only statisitcal averages, not individuals.
> Reductionist as reducing complex behaviour such as psychological skills of M+F to levels of hormones present. Other important factors ignored such as role of media & parental differential treatment which has been found to influence gender. e.g. Williams showed when TV introduced to small Canadian towns (Notel), after 2 years, children (esp.boys) became more stereotyped in behaviour= environment can also influence gender. It is likely Nature and Nurture both influence gender development. Biological differences may result in differing environemnts, furthering gender difference reinforcement.