Ok. I’ve recently published a paper with my mentor and colleagues about the ‘extreme female brain’ hypothesis of mental illness. Basically, the paper makes the case that sex differences in evolutionary pressures predispose females and males toward different prevalence rates and manifestations of mental illness. For example, more males than females are diagnosed with autism and more females than males are diagnosed with depression.

There are a few things to be clear on first:

Even though the title of the hypothesis has the word ‘brain’ in it, the study does not involve direct studies of brains. We extended this hypothesis from a large body of work done by Simon Baron-Cohen, who has made a strong case for autism spectrum conditions (ASCs) as an extreme manifestation of male-typical psychology (1). 

This means that for psychological differences that show sex differences in large populations - such as visuospatial skill (measured by the ability to rotate 3D objects in your mind - on average, males score higher than females on these types of tests) or verbal ability (sometimes measured by one’s ability to generate large lists of similar words on the fly - on average, females outperform males on these tests), those associated with a male-bias tend to show up in an even more male-typical way in people with autism (2-3). 

Therefore, the ‘extreme male/female brain’ is psychologically and behaviourally defined, not physically or neurologically defined - you can’t study someone’s brain scans and definitively assign gender but you can look at psychological test results from large populations and claim that someone falls into a more male-typical or female-typical zone, based on population averages.

Some studies have reported prenatal and postnatal hormonal correlates to the psychological traits as well: for example, children exposed to higher amounts of androgens (masculinizing hormones) in the womb tend to make less eye contact as toddlers than children who were exposed to relatively less androgen activity (4). Generally speaking, females make more eye contact than males (5), so the observation that children who receive higher exposure to masculinizing hormones show a more male-typical behavioural profile (relatively-reduced eye contact), is consistent with the extreme male brain idea.

Side Note  

Why is eye contact important? Well, reduced eye contact is an early symptom of ASCs as well as an important building block for increasingly complex social behaviour. In a laboratory setting, it’s easier to measure a clearly defined and ‘simple’ behaviour like seconds spent making eye contact rather trying to infer a person’s internal experience of a social interaction. So eye contact is a useful variable to measure in these kinds of studies.

The other important thing to be aware of is that when we speak of sex differences, we are talking about small but significant differences at the population level - this means that males can have female-typical psychological profiles and females can show male-typical psychological profiles and people who don’t identify with binary gender categories could show either kind of profile.  The model would predict however that more males than females would show an extreme male brain profile and vice versa.

Because the ‘extreme female brain’ research project is evolutionarily oriented, we are trying to understand the nature of humans as a species; we are not as focused on individual manifestations of behaviour and experiences, though personal experience is very interesting and certainly worthy of study, they are beyond the scope and focus of the article under discussion.

 

Also due to the evolutionary orientation of the research, we do not explicitly address factors such as social and cultural conditioning, which obviously have massive impacts on the way people’s behaviour, psychology, and mental health develops. A complete understanding of human psychology absolutely requires an integration of evolutionary, biological, physiological, cultural, social, developmental, and spiritual perspectives.

Another point to consider is that because evolution focuses on reproduction as the primary means for passing on one’s genetic material to the next generation, trans people and queer people are not as well-studied from this perspective. We can try to understand why evolutionary forces create variation in gender expression, sexual preferences, and sexual orientation but this approach is not part of the scope of the current research project.

With all of the above in mind, I will now highlight the value in applying an understanding of evolved sex differences in human behaviour to patterns of mental health across our species.

Because male and female bodies differ biologically with respect to reproduction and behavioural strategies for successfully creating and raising healthy offspring (and thereby getting our genes into subsequent generations), we can predict that different kinds of psychological and bodily experiences and responses will have differential impacts on female and male reproduction. 

For example, because a female nurses an infant and a male cannot, we can predict that the ability to bond with and nurture an infant will be under relatively stronger selection in humans who are breast-feeding infants or who are spending large amounts of time caring and nurturing a vulnerable newborn.

Perhaps from here, we can dare to presume that the ability to decipher and respond to an infant’s needs would be relatively more important in female evolutionary history than in male evolutionary history - this does not mean that men are not under selection to attend to or to nurture infants and children, it means that the ability to do so was relatively more crucial to female reproductive success than to male reproductive success. In this kind of situation, we would predict that people of different genders largely overlap in their interest and ability in tending to infant needs, but we would expect that the average level of ability to effectively care for an infant across a large population of people would show a female advantage. 

So, the extreme female brain hypothesis implies that certain traits – those of which females show slightly higher interest and ability in relative to males – have a history of being under stronger selection in females relative to males because they contributed more strongly to female reproductive success than to male reproductive success.

Many of these traits appear to cluster around social intelligence and empathic ability: females tend to be better than males at identifying emotions and inferring the intentions of others (6). Many of the studies that assess these skills suffer from a lack of ‘real world’ validity but we can still suggest - with caution - that females tend to be more motivated and gifted in this area than males. Remember, the difference is small but significant at population levels - though some have argued that sex differences are actually very large at population levels (7).

There is also a line of thinking suggesting that social support through friend and kin networks are relatively more important for female survival than male survival – of course all humans need other humans to survive but given the intensity of the birth experience, the need for care after birth, and cross-cultural evidence for shared child-rearing – it suggests that relatively speaking, females benefit slightly more than males through being highly attentive to and skilled in navigating complex social dynamics (6).

Back to the extreme female brain idea: in the paper, we showed that for some diagnostic categories associated with a strong female bias in prevalence (depression and borderline personality disorder), skill in reading emotions was either enhanced (sub-clinical depression) or preserved (BPD) relative to people with no psychiatric diagnosis. For anorexia, which is also female-biased, there were reductions in emotion recognition. Autism (male biased) and schizophrenia (roughly equal prevalence between the sexes but depends on subtype), emotion recognition was also impaired. Reductions in a wide variety of cognitive and emotional skills are very common in psychiatric diagnostic groups as these people are regularly experiencing lack of motivation, challenges in memory, reductions in executive control, and other general deficits that impair or interfere with test performance in laboratory settings.

The fact that an isolated skill (emotion recognition) so relevant to social functioning is actually enhanced or preserved in some people with a psychiatric diagnosis that involves challenges in social functioning is surprising and interesting as it goes against the ‘deficit-oriented’ way of thinking that tends to dominate psychiatry. It also mirrors findings in autism in an interesting way: people with autism often show islets of incredible ability in specific visuospatial skills although they show significant challenges in other tasks.

So the idea is that evolutionary pressures have shaped a slight difference in the average levels of skill sets between the sexes. If we look at overall patterns of social and cognitive skill, we see a more or less normally distributed and overlapping pattern in both males and females with slight differences in the average level of skill and interest between the sexes (females on average outperforming males in social cognitive tasks; males outperforming females on visuospatial tasks).

People in the extreme ends of the distributions for a given skill are at a higher risk of mental illness as they display very low or very high levels of a given trait (low empathy engenders psychopathy, poor eye contact is a step in the autism pathway, excessive rumination is relevant to depression, etc). When selection drives a sex difference in a given trait or ability (like emotion recognition), multiple genetic, hormonal, and physiological systems underlie the sex difference. If any of the systems become slightly perturbed through environmental, developmental, or genetic factors, what can happen is a shift in the level of the given skill toward an even more extreme expression, creating an islet of ability or a deficit, depending on how you frame it. 

Because people in the extreme ends of the distribution are at highest risk and because the average level of skill differs slightly between the sexes, the islets of ability and deficits show up in sex-specific ways: slight enhancements through perturbations to visuospatial skill development are more likely to push males into an extreme zone of expression whereas slight enhancements to social skill development are more likely to edge females into heightened expression of social cognitive abilities.  The enhanced islet of ability might interfere with other aspects of ‘normal’ development: this idea is expressed through the Intense World hypothesis of autism (8), which suggests that enhanced perceptual capabilities in autism (better audio and visual discrimination) interferes with the development of complex social skills.

Another example comes from the borderline personality disorder literature: some authors have suggested that people at risk for this diagnosis have such highly developed social-emotional skills (9, 10) that they end up over emphasizing relationships and over-analyzing interactions, to the point of pain and suffering in the context of relating. A psychoanalyst from the 1970s, Alan Krohn, dubbed this the ‘borderline empathy paradox’ (11).

So the average female is slightly better at eye contact and reading emotions than the average male.

• What happens if we get a subset of females (and the odd male too) who are exceptionally great at these social-empathic skills?

• What if they can read emotions very well, navigate social dynamics very well, and interpret and respond to very subtle social cues?

• What if these gifted people happen to be raised in traumatic homes or in a culture that specifically endangers their sex/gender?

It’s then possible that these gifts are more likely to be transformed into hindrances as the people are spending much time and energy ruminating over social situations and experiencing anxiety about how they are perceived.

What if the culture distorts, represses, and attempts to control these gifts?

These partially formed notions might be evidenced in a rather reversed and strange way when examining the transitions from serfdom to peasantry to waged labour in European history. In Caliban and the Witch, Sylvia Federici argues that state and religious authorities specifically targeted women with health and herbal knowledge as well as women with the ability to inspire large groups of potential revolutionaries in order to instil new oppressive economic legislation. Therefore, the ‘natural’ ability of women to share knowledge with each other and to ‘glue’ social groups together was specifically attacked, indicating that these gifts were particularly evident and threatening to individuals and groups that had rather nefarious aims.

What I’m saying is that women are not relatively more susceptible to depression than men because they are ‘weak’ in some way but rather their social prowess may make them targets in particular environments, which could plausibly create a very upsetting interaction between enhanced social skill, harmful environments, and the development of psychological health.

I’m coming at this from an odd angle as I’ve received a few comments and questions suggesting that perhaps females experience higher rates of depression than males because as a group, females have experienced targeted violence for an extended period of history. Through mechanisms such as childhood conditioning and intergenerational trauma plus the immersion into cultures with narrow, difficult-to-achieve values (beauty, youth, thinness, wealth) where safety and security is regularly undermined through micro-aggressions in personal interactions, plus measurable differences in quality of life (more females living below poverty line), and the vulnerability to rape could plausibly add up to explain the two to one female to male rates of depression.

An evolutionary perspective does not necessitate the framing of the question as ‘is depression cultural/politically/socially created or biologically created’ because this is a poor question. We are biological beings interacting in cultures of our creation in complex biomes that predate our existence considerably. Separating the forces to understand their relative contributions is rudimentary but it is one way of trying to tease apart and understand the multiple interactions that play a role in human well-being.

What I’m arguing is that the foundation of social skills shows a slight sex difference and these differences can be exacerbated through societal, cultural, or personal experiences – such as in a capitalist society where rape might in a sense be ‘encouraged’ or not that severely punished (read Federici for evidence on this during 1400-1700s Europe). I’m trying to highlight the interaction of our evolved nature as males and females while taking into consideration the cultural and social complexity that has shaped our nature to the present day.

Capitalism could perhaps be conceptualized as an extreme outcome of sexual conflict at the level of society, where the conditions have shifted to favour the male reproductive strategy of accusing and defending resources, often at the female’s expense. Obviously humans have a massive range of abilities to be happy, sad, good, and evil: social and cultural conditions can exploit an evolved sex difference to the benefit of some groups over others. It’s the gift of elevated social skills that can actually create social problems. In a sense, the state and patriarchy could be perceived as attacking female-typical social sensitivity and turning these gifts against women (and men), by making women highly self-conscious and vigilant to their surroundings due to both real and perceived threats. Women may be more vulnerable to unsafe social conditions due to their history of relatively greater selection on social skill and empathy plus their dependence on integrated social networks.

To close this rather winding piece of writing, depression cannot be explained by pointing at purely sociocultural or purely biological factors. The extreme female brain idea suggests that on average, women are gifted with powerful social cognitive skills that might act as a double edged sword: gifting us with the ability to navigate and influence complex social dynamics but also putting us at relatively higher risk of over-analyzing, over-thinking, and thus developing depression, and perhaps, at risk of being exploited by systems that recognize the power of a well-connected social group.

***Blog art by Augusto Giacometti***

References

1. Baron-Cohen et al (2011) Why are autism spectrum conditions more prevalent in males? PLoS Biology, 9(6), e1001081.

2. Weiss et al (2003) Sex differences in cognitive functions. Personality & Individual Differences, 35(4), 863-875.

3. Muth et al (2014) Visuo-spatial performance in autism: a meta-analysis. Journal of Autism and Developmental Disorders, 44(12), 3245-3263.

4. Lutchmaya et al (2002) Foetal testosterone and eye contact in 12-month-old human infants. Infant Behaviour & Development, 25(3), 327-335.

5. Alexander & Wilcox (2012) Sex differences in early infancy. Child Development Perspectives, 6(4), 400-406.

6. Reviewed in Geary (2002) Male, female: the evolution of human sex differences, 2nd edition

7. Del Giudice et al (2012) The distance between Mars and Venus: Measuring global sex differences in personality. PLoS ONE, 7(1), e29265

8. Markram & Markram (2010) The intense world theory - a unifying theory of the neurobiology of autism. Frontiers in Human Neuroscience, (4), 224.

9. Dinsdale et al (2013) The borderline empathy paradox: evidence and conceptual models for empathic enhancements in borderline personality disorder. Journal of Personality Disorders, 27(2), 172-195.

10. Park et al (1992) Giftedness and psychological abuse in borderline personality disorder: their relevance to genesis and treatment. Journal of Personality Disorders, 6, 226-240.

11. Krohn (1974) Borderline ‘empathy’ and differentiation of object representations: a contribution to the psychology of object relations. International Journal of Psychoanalytic Psychotherapy, 3(2), 142-165.