Opinion
The extreme male brain theory of autism

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Abstract

The key mental domains in which sex differences have traditionally been studied are verbal and spatial abilities. In this article I suggest that two neglected dimensions for understanding human sex differences are ‘empathising’ and ‘systemising’. The male brain is a defined psychometrically as those individuals in whom systemising is significantly better than empathising, and the female brain is defined as the opposite cognitive profile. Using these definitions, autism can be considered as an extreme of the normal male profile. There is increasing psychological evidence for the extreme male brain theory of autism.

Section snippets

The main brain types

I will be arguing that systemising and empathising are two key dimensions in defining the male and female brain. We all have both systemising and empathising skills. One can immediately envisage five broad brain types (see also Fig. 1):

  • 1.

    Individuals in whom empathising is more developed than systemising. For shorthand, E > S (or Type E). This is what we will call the ‘female brain’.

  • 2.

    Individuals in whom systemising is more developed than empathising. For shorthand, S > E (or Type S). This is what

The female brain: empathising

What is the evidence for female superiority in empathising? In the studies summarised here, sex differences of a small but statistically significant magnitude have been found.

The male brain: systemising

The relevant domains in which to look for evidence include any that are in principle rule-governed. Thus, chess and football are good examples of systems; faces and conversations are not. Systemising involves monitoring three things in order: input–operation–output. The operation is what you did to the input, or what happened to the input, to produce the output.

Autism: an extreme form of the male brain

Autism is diagnosed when a person shows abnormalities in social development, communication, and displays unusually strong obsessional interests, from an early age [35]. Asperger Syndrome (AS) has been proposed as a variant of autism, in children with normal or high IQ, who develop speech on time. Today, approximately 1 in 200 children have one of the ‘autistic spectrum conditions’, which include AS [36]. Autism spectrum conditions affect males far more often than females. In people with

Evidence for the extreme male brain theory

Initial tests of this theory are proving positive 41., 42.. Some of the convergent lines of evidence are summarised here.

The Autism Spectrum Quotient (AQ)

Males in the general population score higher on the AQ than do females, and people with AS or high-functioning autism score highest of all [55].

Sexually dimorphic somatic markers

On measures of finger-length ratio, males tend to have a longer ring finger than their second finger, and people with autism or AS show this trait in a magnified form [56].

Early puberty

Males with autism have been reported to show precocious puberty, correlating with increased levels of testosterone [57].

Familiality of talent

Fathers and grandfathers (on both sides of the family) of

A key symptom explained

Phenomena that are unpredictable and less controllable (like people) leave individuals with autism either anxious or disinterested. Phenomena that are more predictable are highly attractive to them. When they are confronted with the unpredictable social world, they react by trying to impose predictability and ‘sameness’, trying to control people through tantrums and insistence on repetition. People with autism and AS have their greatest difficulties in the playground, in friendship, in intimate

Central coherence versus systemising

A rival theory of the non-social cognitive anomalies observed in autism is that individuals with autism suffer from ‘weak central coherence’ [61]. The systemising account suggests a different view: that people with autism or AS start their cognitive processing by focussing in on the most local details, as an attempted search for whether these might be ‘variables’ in a systemisable domain. This focus on local processing might appear to arise from a deficit in global processing, but from the

Conclusions and future research

The evidence presented in this article suggests that the male brain is characterised by Type S (where S > E), the female brain by Type E (where E > S), and that the autistic brain is an extreme of the male brain (S >> E). Referring back to Fig. 1, development of an autism spectrum condition means their brain type has shifted towards the lower right-hand quadrant. For males, it is a small shift, from Type S to extreme Type S. For females, the shift is bigger, from Type E to extreme Type S. What

Acknowledgements

The following agencies have supported my work during the writing of this article: the Medical Research Council (UK), the Three Guineas Trust, the Isaac Newton Trust, and the James S. McDonnell Foundation. I am grateful to Sally Wheelwright and Johnny Lawson for the development of Fig. 1.

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