biological

• brain sex theory 


  caused by specific brain structures that are incompatible with a person’s biological sex
• particular attention has been paid to this those areas of the brain that are dimorphic - take a different form in males and female
• ning zhou et al studied the bed nucleus of the stria terminalis which is assumed to be fully developed at age 5 and around 40% bigger in males than females
• post mortem studies - 6 male to female transgender individual, the BSTc was found to be a similar size of that of a typical female brain
• post mortem studies findings confirmed by frank kruijver et al who studied the same brain tissue but focused on the number of neurons in the BSTc instead of the volume

  • again the six trans individuals showed a sex reversed identity pattern with an average BSTc neuron number size in the female brain
• frederick coolidge et al assessed 157 twin pairs (96 MZ, 61 DZ) for evidence of GID using clinical diagnosis of criteria in DSM-4


  prevalence of GID estimated to be 2.3% with 62% of the cases accounted for by genetic variance

  • suggests there is a strong heritable component to GID
• gunter heylens et al compared 23 MZ twins with 21 DZ twins where one of each pair was diagnosed with GID


  found that 9 out of the 23 MZ twins (39%) were concordant for GID compared to none of the DZs

  • indicates a role for genetic factors in the development of GID
• X hilleke hulshoff pol et al challenged the assumption that hormone treatment doesn’t affect the BSTc as he found that transgender hormone therapy affected the the size of the BSTc

  • therefore observed differences may be due to hormone therapy rather than a cause of GID
• X difficult to separate the influence of nature and nurture in twin studies as twins may influence each other and the environmental conditions they are exposed to a likely to be very similar
• X hard to make effective generalisations - GID is very rare and samples of twin studies tend to be small
• X reducing complex conditions down to simple genetic and hormonal issues and ignoring other contributory factors occurring at a higher social or psychological level