sex differences lecture 5

sex Differences in Behaviour: Activation Hormonal Effects:

cause
• Variations with varying testosterone levels
• Variations with varying estradiol levels
• Variations with the menstrual cycle

do activational hormones influence sexual orientation?

origin of sexual orientation – activation role of hormones don’t seem to have any influence :

No differences detected in adulthood between different sexual orientations
• Hormone fluctuations, manipulations, or treatments affect sexual motivation, but not orientation

Origins of Sex Differences (sexual orientation) in Brain and Behaviour: organizational hormone effects in males

organisational effect - mostly occurring during early development

There are two periods during development during which T is higher in males than females :
1 - Weeks 8-24 of pregnancy
- Early in this period : when external genitalia
- Late I nthis period : when brain differentiation begins to occur

 2 - First 3 months after birth (short period of peaking testosterone – sometimes called mini puberty)
- potential further brain differentiation

Sexual orientation could potentially occur/ be defined during these periods

However can not check sexual orientation in ¾ month old as thye have no sexual interests at this age

evidence sexual orientation is determined by organisational hormones during early development: list three types of evidence we can source

Evidence for organizational role of hormones: ( all we have is indirect evidence which statistics  due to risk of sampling mother during pregnancy )

Cant get direct samples of prenatal hormones – due to risk of mother and infant during pregnancy:

But we havce indirect evidence :
1 • Correlations with measured prenatal hormones -
2 • Correlations with adult correlates of prenatal hormones

(i.e. we know some things are directly infleuced by early testerone/ prenatal organisational hormones, we can then observe if these identied “early|” hromones also correlate with sexual orientation_

3 • Conditions with varying (atypical) prenatal hormone levels
individuals who experience atypical hormone levels during development

– Congenital Adrenal Hyperplasia (CAH) XX individals – abnormally strong testosterone levels during developement
– Androgen Insensitivity Syndrome XY indivdiuals – individuals who don’t respond to testosterone

evidence sexual orientation is determined by organisational hormones during early development: explain Correlations with measured prenatal hormones -

Correlations of embryonic/ prenatal Testerone observed during child and adult measurements –

all produce small but replicable effects

1. - Cognitive performance
• Verbal abilities are better in androphile men than gynephile men (on average women talk in more complete sentences than men do and coincidently found this fact)
• Visuo-spatial performance is worse in androphile men than gynophile men
• Mental rotation is faster in gynophile women than in androphile women (a stereotypical task men excel in)

2 - 2D/4D ratios (difference in Length of second digit (index digit) compared to 4^th digit (ring finger)

Sex differences in 2D/4D ratios (male: 0.95 sho, female 0.97)
• 2D/4D ratios are  Early testosterone dependent

Evidence - Evidnce these differences occur in other species -rats/birds – evidence they exist in rats, and occur dependent on early T levels in rats/ birds - providing some evidence that it is an indicator of early testosterone.

 

Observation in humans
• most consistent results in relation to sexual orientation are in relation to gynophile women  - Butch lesbians have more masculine 2D/4D
• No consistent finding in androphile men, but may differ between sub-groups as 2D/4D correlates with gender non- conformity (Swift-Gallant et al., Sci Rep 2021) as studies evidence

Androphile men which have stronger gender non-conformity present with more feminine 2-4 rations, than androphile men with less gender non-conformity

More masculine presenting gynophyle women present more masculinised 2-4 rations than more female presenting androphile women

Indicates that lower/ higher T levels during development influence sexual orientation

3 - Oto-acoustic emissions - When human stimulated with a click next to someone’s ear, (if you place a microphone next to ear the) ears make a sound back

• auto acoustic emissions are louder and more frequent in women (and females of other species)

• studies within other species evidence auto acoustic emissions are Early T- dependent in other species

• some evidence Gynophile women’s (lesbian women) OAEs closer to gynophile men’s than androphile women’s (women attracted to men)

 

evidence sexual orientation is determined by organisational hormones during early development:/ evidence for organisational role of hormones - conditions which prenatal hormones vary from the norm

Congenital Adrenal Hyperplasia (CAH)

• CAH females are also more likely to identify as gynophile

  within a study 40% of CAH participants identified as bisexual/ gynophile

• suggests that having been exposed to early testosterone during prenatal development is a factor that biases you to sexual orientation/ gynophylic within adulthood

• Androgen Insensitivity Syndrome

• Most evidence points towards a role of prenatal testosterone in developing as a gynophile adult. - it is an evident factor

• But this is not the only factor.

Origins of Sex Differences in Brain and Behaviour (sexual orientation: genetic factor

another factor

genetic effects evidenced via

• Twin studies

• Genetic mapping

• Concerns from an evolutionary angle

• Fraternal Birth Order effect

Origins of Sex Differences in Brain and Behaviour (sexual orientation: genetic factor - explain twin studies

Twin studies

◦            Higher concordance  (sexual orientation more similar) in monozygotic than dizygotic twins

◦            Estimates from 30-100% increased concordance varying depending on study type

◦            Possibly higher concordance for women than men

Infer there is a genetic component which infelunces sexual orientation

Origins of Sex Differences in Brain and Behaviour (sexual orientation: genetic factor - Genetic mapping

 

Genetic mapping

◦            Androphilic (gay) men often have androphilic maternal uncles

◦            Suggests an X-chromosome inheritance pattern

◦            A region of the X-chromosome has been identified as related to sexual orientation

◦            Regions on other chromosomes have also been identified

Origins of Sex Differences in Brain and Behaviour (sexual orientation: Concerns from an evolutionary angle/ evolutionary concerns

·   will homosexuals not have fewer offspring? -

• How does a putative genetic basis not get selected out of the population then?

• Evolutionary argument-  hwo can there be a genetic basis for homosexual orientation if it reduces fertility

Response argument :

• Possible mechanisms for maintaining such genes:

• Fraternal birth order effect: the odds of having a boy who is androphylic, increase based on how many boys that mothe has previously birthed, could be an immune response, as developing male foetus produce unfamiliar genes, which only male embroy expresses – female embryos don’t express it – so may be male specific proteisn mothers produces antibiodies againr, resulting in gene alteration during foetal development of males

• Evidence - Fraternal Birth Order Effect:Maternal immune hypothesis

2017 study. Evidenced Mother's immune response to protein neuroligin 4 Y-linked predicts probability of having an androphile son (Bogaert et al. PNAS 2017)

• Heterozygote advantage: like e.g. cycle cell anemia – if there is gene that in its homozuygous state -  if there are two copies makes an idnvidial a homosexual , therefore inhibiting offspring from being produced , but if only one copy/ half the gene exists in an individual , it could have advantages such as e.g. survival advantages – explaining why it has persisted in its presence despite evolution

• Genes have Different effects in males vs females – within a family: gene that makes male more likely to be androphylic, could also make female sister moreliely to have children/ produce offspring – enabling gene to be maintained in population via female line: 2004 paper evidenced that maternal relatives of male homosexuals have more children.

• Evidencing this as a possibility

• Kin selection – if there were a gene which influenced sexual orientation in men = make them gay, that person would support sister in raising family, so pass on genetic indirectly via kin selection

Sexual Orientation:

Conclusions

◦            Clear biological developmental influences

◦            No influence is absolute

Sexual orientation can be influenced by a number of different factors

What about Gender Identity?

◦            Gender identity has a larger sex difference than sexual orientation

◦            Does not seem to be binary – some people identify as non-male and non-female

◦            Childhood gender dysphoria does not always continue after puberty (does for ~40%)

What influences gender identity? - genes?

◦            Not a single phenotype

◦            Genetic predispositions to gender dysphora

◦            Study examined transgender idnvidials abd controls: cis males/females

Conducted a genetic mapping exercise – found some particular alels / genes that are correlated/associated with gender dysphoria

Trans men: having long version of oestroen receptor beta and long version of oestrogen receptor alpha strongly corelated with beign transc- suggesting these genes madee them more liely ot be trans

Trans women havel ogn version fo androgen receptor beta and short version of the oestrogen receptor beta , biases them towards being trans women

Sex genes involved in sex hormone signalling trongly correlate – within transgender male and female individals – suggesting gentic involvement in gender identity

 

Suggesting genes are involved in gender identifty

What influences gender identity? - brain diferences?

Pre transition brain differences –

◦            Brain volumes are in line with natal sex

◦            MtF (male to female)  individuals show more feminine cortical thickness and white matter in some brain areas

◦            FtM individuals show more masculine basal ganglia and some white matter tracts

Evidencing Some aspects of brain anatomy are different from both cis males and cis females

gender identity conclusions?

◦            Genetic and hormonal factors cause sexual differentiation

Different aspects of brain and behaviour can be masculinized or feminized, leading to a wide diversity of combinations of "gendered" traits