Sex and Differences ||

Question 1

Hormonal modulation of sexual and aggressive behaviour
1. what are steroid hormones important for?
2. what do castrated mammals show?
3. what are changes in reproductive behaviour tightly correlated with?
4. What reinstates sexual behaviours?
5. What has much less effect?

Answer 1

1. Steroid hormones are important in modulating aggressive and sexual behaviours.
2. Castrated male mammals show reduced sexual and aggressive behaviour (e.g. stallions / geldings, bulls / heifers). Spayed female mammals show reduced sexual behaviour (e.g. cats, camels). Well known for at least several thousand years.
3. There was a time where cammals were used- males cammals were placed miles away to distract the female- removing the ovaries of cammals would stop behaviour
4. Changes in reproductive behaviour are tightly correlated with changes in hormonal secretion (e.g. in red deer, the rut is highly correlated with increases in testosterone in the male during autumn).
5. Replacement of steroid hormones after either castration or ovariectomy reinstates sexual behaviour.
6. but removal of hormones in sexually experienced adult animals may have much less effect - so a strong interaction with learning / experience over a lifetime. This is likely to be especially true in humans. When humans are sexually experienced the sexual aspect after is still rather present.

Question 2

‘Organising’ and ‘activating’ effects of hormones

A classic experiment reported in 1959 first demonstrated that androgens could have effects on behavior that persisted well beyond the time that they were present (‘organizing effects’) in addition to relatively immediate effects (‘activating effects’).

Answer 2

Control- normal pregnancies
Experimental group- testosterone was administered during pregnancy

Ask what happens if now you take the female gp, remove their natural source of hormones and then in the first part of the experiment those gp are fed with female type steroides. What the gp do in that situation is they show a behaviour called ordosis. This is the behaviour that occurs if they are ready to mate with the male.
Then you wait and let the effect of those hormones dissapear and then you treat with testosterone. Those females who were responsive to testosterone in the process would show the appropriate behaviour (attempt to mate with the male)

Guinea pigs were exposed to testosterone prenatally, and then failed to show female sexual behavior
as adults. However, unlike control animals) they responded to adult treatment with testosterone by showing male sexual behavior
(Phoenix, et al. (1959) Endocrinology, 65, 369–382.

Effects of hormones early on in life has an affect on hormones in their later life

Question 3

‘Organising’ effects of hormones:
Evidence from congenital adrenal hyperplasia

Answer 3

• Congenital adrenal hyperplasia is an inherited recessive condition in which a loss of an enzyme in the pathway for aldosterone synthesis (typically 21-⍺-hydroxylase) leads to excess androgen production by the adrenal gland during foetal development. It has relatively small effects on boys, but leads to physical masculinisation (‘virilisation’) in girls.
• See- substantial effect in girls which is absent in the boys
• It is also related to toy choice in young girls. Additional evidence suggests that any parental influence would reduce rather than enhance the effect.
• Hines’ short review describes the way in which a similar type of effect may be observed in vervet monkeys.

Question 4

Sex differences in human aggressive behaviour

Answer 4

• A recent metanalysis confirms that there are large or very large (Cohen’s d values around 1) sex differences in weapon use, violent crime, homicide and violent computer-game use, and also in rape (Archer 2019).
• Darwin (1871) suggested that competition between males for access to mates leads to sex differences in size, strength and aggressive behaviour. Extended periods of maternal care for infants may be associated with avoidance of the risks associated with aggressive encounters.
• due to competing for females therefore leading to sex and behavioural differences
• The difference in aggressive behaviour emerges before puberty but there is no direct evidence to suggest that it depends on prenatal hormonal exposure.
• It’s important to note that some of the differences in aggressive behaviour are in the tail of the distributions. Even if biological factors play a part, they are likely to be (strongly) modulated by social and other environmental influences.
• organizing effects- effects emerge before puberty but there isn’t
• note you are looking at effects of the tail of the population

Question 5

Organising’ and ‘activating’ effects of hormones: two human studies - 1

Answer 5

Study of traders in financial derivatives at a London bank (260 males– just 4 women in sample). Measures of testosterone levels at 11.00h and 16.00h – related to profit or loss for the day.
Individuals who have higher testosterone levels in the morning in two ways:
* overall they were more successful
* there was much greater variance in their performance- some did bad, some did very well
Its likely this effect is related to risk taking behaviour

High testosterone at 11.00h predicts greater profitability for the rest of the day. An ‘activating’ effect?
Cortisol levels were high when individual returns were more variable.

Question 6

Organising’ and ‘activating’ effects of hormones:two human studies - 2

Answer 6

Used a controversial measure of organising effects
Study of traders in financial derivatives on a New York trading floor. Measures of digit ratio (2D:4D)
– related to long term profit or loss records
(Coates et al. (2009) PNAS 106:623).

A low 2D:4D ratio is associated with high levels of fetal testosterone. This ratio was able to predict profit and loss- when ratio is low high testosterone exposure
These data show it is also associated with higher success on the trading floor. An ‘organising’ effect?

Two obvious issues with these data in relation to sex / gender differences:
* Virtually no female participants
* Studies of adults completely confound biological with environmental and cultural influences

Question 7

Androgens and sport

Answer 7

Synthetic androgens (e.g. nandrolone) have been widely (ab)used, by both men and women, for their performance enhancing effects in sport:
* Increase lean body mass (e.g. muscle tissue)
* Stimulate red blood cell production- important for stamina
* Enhances visuospatial neural activation
The relative effects of increased androgen levels in women may be greater (2% - 5% increase in performance).
So what should be the position of women with naturally high levels of androgen production?

Caster Semenya is an intersex cisgender women, assigned female at birth, with XY chromosomes and naturally elevated testosterone levels due to 5a-Reductase deficiency.
Dutee Cahnd, an Indian female athlete with naturally high androgen levels (physiology unknown) has supported Semanya

Question 8

What is there evidence for in elite performance in some sports?

Answer 8

There is evidence for sex differences in elite performance in some sports.
800m world record 101s (112s in 1912) 113s (150s in 1922)
(100m not reliable in early records because of short timing)
The trend in female performances down wards is much stronger
There is also limited evidence that women with naturally higher androgen levels (T)
may perform better in some events but not others:
100m 11.9s (low T) 12.1s (high T) ns
800m 121.8s (low T) 120.5s (high T) *

… the difference was only significant in 4 of 21 events, though sample sizes are small (Bermon & Garnier 2017). Does this justify a high T cutoff in women’s elite sport.

• Many other differences between individuals affect sporting achievement, especially at elite levels. These include weight, height and lower body symmetry.
• Should events be subdivided using such criteria? It happens in boxing, wrestling and weightlifting. Weightlifting has 10 weight classes as well as separating the events by sex!

Question 9

Sporting status of trans athletes

Are testosterone levels the appropriate marker to use?

Answer 9

The position of individuals who transition from male to female status has been especially controversial. Drug treatments, such as a GnRH antagonist, will greatly reduce testosterone levels. In many sports a consistently low testosterone level is taken as a marker for ‘fair’ competition by trans women.
However this does not abolish the sexual dimorphisms in
muscle size and strength that begin at puberty.

The decrease in the graph is rather small and the sex difference in still there

Biology won’t provide a neat answer to these sporting dilemmas.

Question 10

Oxytocin and vasopressin also act as neurotransmitters within the central nervous system

Answer 10

Affect affiliative behaviour
The neurotransmitter is secreted into vesicles within the presynaptic terminal. When the presynaptic neuron becomes active the neurotransmitter is released, diffuses along synaptic cleft and activates neurotransmitter receptors on the membrane of the postsynaptic cell.

Question 11

Species differences in mating systems

Answer 11

The most common pattern of care in mammals is care by female alone. However stable pair bonds, with care of infants by both parents, are also found in some species, though relatively rarely.
Different patterns of mating systems and affiliative behaviour

Prairie voles have stable pair bonds and both parents care for the young.

… but meadow vole (live in a more open environment) males move on from one female to another and do not take care of the young.

So… Whats the basis of this difference in mating systems

Question 12

Oxytocin and vasopressin are important in the development of the pair bond in prairie voles

Answer 12

Extra oxytocin (OT) or vasopressin (AVP)
strengthens pair preference, but blockade
of receptors (antagonist) weakens pair
preference.
Further experiment suggest specific learning
-related effects.

If you take a female vole and place her with a male, then if you treat her with oxytosin then you can greatly increase her preference for spending time with that male. Therefore oxytosis enhances preference.
If you take a female who has already paired up with a male and now you treat her with an oxytosis antagonist then that greatly reduces her preference for spending time with the male.
If you take a male and treat him with AVP- it greatly enhances. But if treat with an antagonist- greatly reduced.

Question 13

Large numbers of oxytocin receptors are present in the prairie vole (left), but not the meadow vole (right)

Answer 13

When looking at brains of voles for the density of oxytosis receptors, there are big differences between the species.

The black areas are those with high density of oxytocin receptors. They are concentrated in an area associated with reward-related learning.

Question 14

Distribution of vasopressin receptors in prairie and meadow voles

Answer 14

Monogamous prairie vole: Time spent huddling was higher than in polygamous meadow voles

Question 15

Adding vasopressin receptors to the meadow vole brain increases the tendency to form a pair bond

Answer 15

Here vasopressin receptors have been introduced into the meadow vole brain by using a viral vector.
Again the measure of pair preference is greatly increased - so confirming that the meadow vole produces vasopressin, but does not normally express the relevant receptors.
All of these studies have been carried out by Thomas Insel (reading on final slide).

Meadow voles now began to express strong preferences

Question 16

Are there implications for human behaviour?

Answer 16

You can buy sprays of oxytocin if you’re trying to attract people to you

There may be a similar difference in the expression of oxytocin receptors in some primate species:

• Lower expression in the bonobo (close relative of common chimpanzee with highly promiscuous mating system) than in common chimpanzee
• Some evidence that oxytocin may have similar effects in humans.
• So, there may be important biological influences on patterns of social and sexual behaviour.

Question 17

Mating systems and sex differences in primates

Answer 17

Considerable variety which is influenced by the ecological niches that they inhabit. Some
examples:
* Common marmoset – small South American primate lives in dense jungle. Stable pairbonds, little size dimorphism, female typically has twins.
* Ringtail lemur - from Madagascar, lives in small groups in which females aredominant, daughters stay, sons leave, little size dimorphism
* Hamadryas baboon – African savanna and arid areas. Males x2 size of females, maleharems, organised into bands and clans.

Question 18

Evolutionary history of apes

Answer 18

Figures from Langergraber et al., 2012 (top), Segre & Salafsky, 2016 (bottom).
* Gibbons (not shown – the ‘lesser apes’) diverged from other apes about 17 millionyears ago (Ma). They are forest living, arboreal, have little sexual dimorphism and often have long term pair bonds.
* The great apes comprise gorillas, chimpanzees, bonobos and humans (top figure). Humans diverged from the chimpanzee / bonobo line about 8-10 Ma.
* The lower figure shows the way in which the gut flora has co-evolved in the ape line.
Likely to be driven in part by dietary changes.

Question 19

Mating systems and sex differences in great apes

Answer 19

Again, considerable variety including:
* Gorillas: forest living knuckle walkers and tree climbers, diet of vegetation and fruit (when available), considerable sexual dimorphism (male up to twice weight of female), live in troops with adult male (occasionally more than one), group of females and their offspring. Aggressive male encounters between troops.
* Chimpanzee: Males 1.5 size of females, flexible social groups (fusion-fission structure).
* Bonobo: smaller than chimpanzee, less sexual dimorphism, social structure dominated by matriarchs, notably less agression within groups than in chimpanzees.

Question 20

Mating systems and sex differences in apes:
Implications for human behaviour?

Answer 20

• There are substantial differences between species that diverged relatively recently in evolutionary time (e.g. chimpanzee and bonobo), even when they inhabit relatively similar ecological niches. So any comparisons with our “nearest relatives” should be cautious!
• Dawkins (in The Selfish Gene, 1976) wrote “… if you wish, as I do, to build a society in which individuals cooperate generously and unselfishly towards a common good you can expect little help from biological nature”. His draws parallels, on the same page, between humans and baboons.
• Frans de Waal (in Different, 2022) quoted Dawkins and disagreed. He argues that apes (including humans) have a long evolutionary history of successful group living and have developed cognitive abilities that facilitate it.
• Hrdy (2020) takes this argument further, suggesting that cooperative breeding in primates, including humans, promotes social tolerance and proactive sociality.

Question 21

Sex / gender differences in cognition

Answer 21

Although there are many cognitive tasks in which sex / gender effects have been claimed, the differences are frequently small (less than 0.5 SD) and unreliable. For comparison the height difference is large (2 SD) and highly reliable. In a recent meta-analysis (Archer 2019) most of the large effects identified involved an excess of male aggression / violence.

However mental rotation is an example of a task in which the gender difference may be both more reliable and substantial (male advantage).

The ‘virtual’ Morris Water maze is a more recently described example of a ‘spatial’ task in which there is a male advantage.

The effects are more reliable where you do in fact have a male advantage

Question 22

Are the sex differences in these tasks related to biological variables?

Answer 22

Recent data on the virtual water maze provides some insights:
* Androgen receptors located widely in brain, including hippocampus.
* Men with more sensitive androgen receptors, due to fewer CAG repeats in the gene for the receptor (as in a different gene linked to Huntingtons diease) make fewer errors on the virtual water maze if their T level is relatively low1. Consistent with optimum T level theory proposed earlier.
* Can distinguish navigation using allocentric (spatial map) or egocentric (local landmark) strategies –the former may be hippocampal dependent whereas the latter depends more on parietal cortex / basal ganglia mechanisms. No evidence of differential use of these strategies by men and women2.

Question 23

Autism and autism spectrum disorder (ASD):the (controversial) extreme male brain hypothesis

Answer 23

Baron-Cohen et al (2005) suggest that autism and ASD can be understood in terms of the tendency to systemise (male-typical) or empathise (female-typical): looks at 2 aspects of behaviour
* Sytematise; to understand a system, or others behaviour, in terms of rules.
* Empathise; to understand a system, or others behaviour, by identifying mental states and responding with an appropriate emotion.
Find that people with autism/ ASD tend to be on the extreme male side

Note that the AS/HFA group fall into the lower RH quadrant and that there is some degree of separation in the control male/female data – though very substantial overlap.

Studies examining the relationship between foetal testosterone exposure and AS/HFA have been inconsistent. (e.g. Baron-Cohen et al. Molecular Psychiatry 2019, online).

This leads to the possibility that there could be treatments that leads to opxydosin

Question 24

Autism: diagnosis, brain connectivity and treatment

Answer 24

There is strong evidence for a genetic influence on ASD but likely to be a cluster of disorders associated with different gene variants, and interacting with social and environmental factors.
ASD is also diagnosed much less frequently in females (1:4 ratio). Is this a real
difference or are male–derived diagnostic criteria inappropriate for females?
A recent large scale, replicable fMRI study suggests that patterns of brain
connectivity differ between males and female participants with ASD and are
different from any sex differences in the brains of neurotypical individuals.

Based on the potential oxytocin/empathy connection, human trials of an intra-nasal oxytocin spray are underway2 but two obvious

problems:
* heterogeneity in ASD – oxytocin may only be effective in subgroups.
* Epigenetic changes in early development may lead to decreased oxytocin receptor function3.

Question 25

Concluding thoughts from Halpern (2000)

Answer 25

There are likely to be strong, and continuing interactions between a variety of biological variables that influence current behaviour.

Attempts to dichotomise these influences into additive effects of ‘nature’ and ‘nurture’ are inappropriate.

Hypotheses about putative sex / gender differences should address the very substantial within gender differences as well as those between genders that are often of small size