Why does autism exist?

Why does autism exist? I have asked myself that question several times and wondered about the answer. If autism is indeed a “disorder characterised by persistent challenges with social communication, restricted interests, and repetitive behaviour,” then why did the genetic variance that causes autism not simply die out from an evolutionary perspective? Well, quite a few people who know much more about genetics than I do have also asked that question.

 Prof Simon Philip Baron-Cohen (yes, the brother of Sasha), the director of the University of Cambridge’s Autism Research Centre, explores this question in his book, The Pattern Seekers: How Autism Drives Human Invention. In the book, he argues that all human innovation stems from what he terms the ‘systemizing mechanism’ — the ability to discern and manipulate causal patterns. This cognitive mechanism, Baron-Cohen says, is particularly strong in innovators in all fields — the arts as well as the sciences — and also in people with autism, two groups that he believes have overlapped throughout history.


Autism and Intelligence

His theory is supported by Renato Polimanti and Joel Gelernter in their 2017 study, Widespread signatures of positive selection in common risk alleles associated to autism spectrum disorder. “It might be difficult to imagine why the large number of gene variants that together give rise to traits like ASD are retained in human populations — why aren’t they just eliminated by evolution?” says Prof Gelernter. “The idea is that during evolution these variants that have positive effects on cognitive function were selected, but at a cost — in this case an increased risk of autism spectrum disorders.”

Similarly, a team of researchers from Ohio State University, led by Joanne Ruthsatz found a clear correlation between the genetics of autism and high intelligence in their study, Molecular Genetic Evidence for Shared Etiology of Autism and Prodigy.  According to Ruthsatz, “It was like, here it is, here’s the autism and the prodigies together and they have a significant peak on chromosome 1, where they are significantly different than their non-affected family members.” The study says that “This finding suggests that a locus on chromosome 1 increases the likelihood of both prodigy and autism in these families.”

In an article written by Bernard Crespi, of the Biological Sciences and Human Evolutionary Studies Program of Simon Fraser University in Canada, he says that the “high intelligence imbalance” hypothesis predicts that autism should be associated, at a phenotypic level, with substantiated correlates of intelligence. He reviewed several studies of the genetic overlap of autism with intelligence and found that increased sensory discrimination ability in autism represents a strong correlation to intelligence that is frequently enhanced to the point of imbalance with other aspects of IQ. Hyper-functioning of these regions may thus result in imbalanced intelligence, whereby efficient integration with downstream regions, especially parietal regions that subserve symbolism, abstraction and categorization of sensory information, becomes dysregulated.


But what about natural selection?

As autistics, we all know that there is a link between autism and high intelligence. The fact that some of us a good at maths doesn’t make the rest of the world easier.

In the 2016 meta study, Are there alternative adaptive strategies to human pro-sociality? The role of collaborative morality in the emergence of personality variation and autistic traits, by Penny Spikins, Barry Wright &Derek Hodgson, they note that we might imagine that autism would imply limited reproductive success, but state this is not the case. In modern hunter-gatherer contexts such traits are rarely of primary significance in mate choice. Amongst the Hadza for example the most significant trait affecting female mate choice is being ‘a good hunter’ Food is shared widely so that hunting prowess does not confer direct nutritional advantage to one’s kin; however, good hunters are more reproductively successful in attracting mates. Intelligence is also significant and the primary consideration for someone to be seen as ‘nice’ is not astute social skills but non-violence.

They argue that, after the rise of collaborative morality (an investment in the well-being of everyone in the group) about 100 000 years ago, a social niche arose for individuals with autism whose logic-based theory of mind was a viable alternative perceptual strategy to a ‘neurotypical’ complex theory of mind, bringing with it valued social and technical talents. The emergence of technological or social innovations which improve survival, in turn, create a niche to which the characteristics of those with autism are particularly suited.

For example, environments associated with unpredictable resources might have been particular ‘hotspots’ where traits of autism were most valued. In such situations a focus on detail and a high level of standardisation to ensure maintainability and reliability, is essential for survival, and emerging specialised roles would provide the scaffolding for such autistic traits to be developed and valued. Abilities at focusing on and providing technological solutions will have been particularly valued, especially where changing environments put survival at risk.

Crespi also argues in his study, Developmental heterochrony and the evolution of autistic perception, cognition and behaviour, that hunters had to be able to predict the patterns of game movement through the seasons (a repetitive behaviour), endure solitude while hunting (an antisocial state), and make and invent tools (a mechanical action). Thus, he hypothesized that the autistic brain is an example of an "extreme male brain" that initially evolved to cope with the demands of hunting. In hunter-gatherer societies, these traits allowed males to survive and provide for their families However, these traits no longer provide the same benefits in the context of our modern world.


Personal View

I started asking myself the question about why autism exists during all the lockdowns, when I had lots of time to observe my children and think. I’ve developed the view that maybe autism is an evolutionary back up plan. When the environmental conditions change very rapidly and actions that neurotypical people view as “safe” are no longer safe, that’s when the back up plan kicks in. Social distancing is not a problem for most of us – in fact, I suspect that my son didn’t even notice we were in lockdown for the first couple of weeks.

Perhaps all of these studies can be summarized by two quotes from Temple Grandin, in her very blunt way:

“What would happen if the autism gene was eliminated from the gene pool? You would have a bunch of people standing around in a cave, chatting and socializing and not getting anything done.”

“People talk about curing autism. But if you got rid of all those traits, who's going to make the next computer?”

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