This article is about whether the concept of an ‘extreme male brain’ has any explanatory power for autism. Clinical autism is more common in men than women, and amongst people who do not have a diagnosis of autism, men score somewhat higher than women, on average, on questionnaires which assess behaviors that are common in people with autism. These questionnaires score interests in how things work, known as ‘systemizing’ as ‘male’ and interests in other people’s emotions and thoughts, known as ‘empathizing’ as ‘female.’ This has led to the view, proposed Simon Baron-Cohen and his colleagues, that people with autism have an ‘extreme male brain’ (1). But what does it mean to say that a brain is ‘extremely male’?
Men and women differ, on average, in many aspects of anatomy, physiology, and behavior, but these differences do not necessarily vary together. On average, men have bigger feet than women, and, on average, men are more interested in trains than are women. But men with big feet are probably no more interested in trains than are men with small feet, so, which is the more ‘extreme male,’ the man with big feet or the man who likes trains?
Most of the things that differ between men and women consist of externally definable measures. For example, on average, men have more muscle strength than women where muscle strength can be measured experimentally. But ‘being male’ is internally defined – it can only be measured against what males are actually like. Being an ‘extreme male’ can only mean being an ‘extremely normal male,’ not being an ‘extremely unusual male.’ Most crimes of violence are committed by men rather than women, but that does not mean that a violent man is ‘manly.’
On the Baron-Cohen Autism Questionnaire (AQ), which has scores from 0–50 and on which high scores are regarded as indicative of autistic-like behavior, men from the general population scored ~18 and women scored ~15, a difference of 3 points. Men with autism scored ~36 and women with autism scored ~39, again a difference of 3 points (2). But the difference between people with autism and people from the general population was ~18 points. People with autism resemble each other but differ substantially from other people. A woman with autism is not like a man; she is like other people with autism. Autism is a clinical condition; being male is not.
As scientists, we no longer believe, as did the philosopher Descartes, that the mind is some kind of immaterial substance that inhabits the body, including the brain. Rather, we accept that the mind is ‘embodied’ in the brain, that is to say, that the brain is active when we move or think or perceive the outside world. ‘Me’ and ‘my brain’ are not two separate things; they are two aspects of the same thing. So, in a ‘soft’ sense, if I behave in a male-typical way, then my brain must be acting in a male-typical way. If I behave in an autistic way, then my brain must be acting in an autistic way. But science is about explanation, and the ‘extreme male brain theory’ of autism is making the ‘hard’ claim that there is something specifically male about the structure of the brains of people with autism. Scientific research could investigate this, but what would it mean to say that a brain is ‘male,’ let alone ‘extremely male,’ when it occurs in a woman with autism? To describe a woman with autism as having ‘an extreme male brain’ is logically equivalent to describing a very tall woman as having ‘extreme male height’ because, on average, men are taller than women. However tall she is, she is just a very tall woman. Neither description has any explanatory power.
In most people, there is no discrepancy between the various ways in which they are male or female. The presence of a Y chromosome, appropriate levels of male hormones, male genitalia, and male secondary sexual characteristics (for example, a deep voice), male-typical interests and behavior, and a sense of male identity all occur together in a typical male. The equivalent female characteristics all occur together in a typical female. But genetic, hormonal, and anatomical anomalies can occasionally occur in different individuals, and it is then a problem to privilege one factor over another in order to ascribe a sex to a person. Furthermore, interests, behaviors and a sense of gender identity vary widely from one person to another. This is just human diversity. So for the ‘extreme male brain theory’ to have any explanatory power in understanding autism, there must be something biologically different about the brains of people with autism compared to the brains of people who are not autistic. Some researchers are indeed looking at ways in which the brains of people with autism differ from those who do not have autism, but to argue that the brains of such people must be different because they have high AQ scores (which is true in the ‘soft’ sense) while also arguing that such a brain anomaly ‘explains’ the high AQ score is circular and, therefore, unhelpful.
We know from the AQ questionnaire that people with autism usually have high AQ scores. But can the AQ be used to help detect people with autism? This is a subtly different question. In a study which looked at the scores of people who already had some sort of mental health difficulty, AQ scores did not distinguish between people who were subsequently given a diagnosis of autism and those who were given a different mental health diagnosis, particularly ‘generalized anxiety disorder’ (3). Some people who were found to have autism did not score highly on the AQ, and, indeed, people who were given a diagnosis of autism but who did not also have a generalized anxiety disorder were particularly likely not have high scores on the AQ. So high AQ scores may not be specific to autism when compared to other mental health difficulties and so do not help to provide a differential diagnosis.
At present, there are no aspects of brain structure, or physiological or hormonal effects, which are diagnostic of autism and which can be related to brain differences between men and women. The brain is like other parts of the body in showing certain average differences in size and shape between men and women but all these brain differences show some overlap between men and women such that no brain structures are found only in men or only in women (4). Considerable effort has been made to investigate whether exposure to sex hormones before birth can produce autistic symptoms after birth. But while prenatal exposure to hormones affects brain development and abnormal exposure can result in abnormal development, these effects have not been found to be specific to autism since further developmental abnormalities may also occur.
The idea that there is such a thing as an extreme male brain is an example of ‘Essentialism,’ which is the philosophical idea that things have a set of characteristics that make them what they are. An essentialist would argue that there is such a thing as ‘maleness,’ with the implication that men deviating from this maleness are not truly male, rather than that variation between men merely makes maleness more diverse. But being male, like being female, involves no more and no less than being everything that males or females are. Many people are still stereotypical in their way of thinking, but in recent times we have developed a greater awareness of the complexity of sex and gender and are moving away from this essentialist thinking.
- Baron-Cohen, S. (2002). The extreme male brain theory of autism. Trends in Cognitive Science, 6, 248–254.
- Ruzich, E., Allison, C., Smith, P., Watson, P., Auyeung, B., Ring, H., et al. (2015). Measuring autistic traits in the general population: A systematic review of the Autism-Spectrum Quotient (AQ) in a nonclinical population sample of 6,900 typical adult males and females. Molecular Autism, 6 1-12. Erratum: Molecular Autism 6, 45.
- Ashwood, K. L., Gillan, N., Horder, J., Hayward, H., Woodhouse, E., McEwen, F. S., et al. (2016). Predicting the diagnosis of autism in adults using the Autism-Spectrum Quotient (AQ) questionnaire. Psychological Medicine, 46, 2595–2604.
- Ruigrok, A. N. V., Salimi-Khorshidi, G., Lai, M.-C., Baron-Cohen, S., Lombardo, M. V., Tait, R. J., et al. (2014). A meta-analysis of sex differences in human brain structure. Neuroscience and Biobehavioural Reviews, 39, 34–50.