Biology | Is Autism Being Positively Selected For?

Autism Spectrum Disorder (ASD) is a neurodevelopmental condition characterised by difficulties in social interaction, communication, and repetitive behaviours. 

Recent research has sparked debate about the potential evolutionary role of autism. It has been proposed that particular genetic variants associated with ASD may have been positively selected due to their cognitive benefits. If true, it's likely this trend has continued in the modern world, where technical STEM-related sectors have become increasingly dominant, whilst traditional non-technical sectors are in decline.

The Heritability & Genetic Landscape of Autism

ASD is understood to be a heritable condition, with estimates of genetic influence thought to be between 74-98%. It is generally considered a polygenic disorder, meaning its manifestation is influenced by multiple genes, although some monogenic conditions have been found to have a strong association with ASD. The polygenic nature of the condition is one of the reasons why there is such a wide range of symptoms and severities, and why its classification as a spectrum disorder remains the most efficient model.

Twin studies have shown that concordance rates in identical twins are high, but fall short of the 100% figure that would allow researchers to classify it as a purely genetic condition. This means a number of environmental factors likely play a role. Current research suggests these factors may include prenatal and perinatal complications, environmental chemical exposure, advanced parental age, maternal nutritional deficiencies, and maternal infections during pregnancy.

So, What Is The Evolutionary Mechanism Behind Autism?

Well, there are a number of different theories floating around, none of which, as of yet, have obtained enough evidence to be seen as definitive. However, the idea with the most traction in the scientific community and perhaps most supported by the data is the Empathizing-Systemizing (E-S) theory proposed by Simon Baron-Cohen.

In a nutshell, the theory posits that individuals with ASD exhibit enhanced systemizing abilities – the capacity to analyse and understand systems – whilst simultaneously facing challenges in empathising, or understanding and responding to the emotions of others. The idea is that these heightened systemizing abilities may have conferred evolutionary advantages in certain environments, contributing to the persistence of ASD traits within the population. 

A 2017 study conducted by Yale University researchers seems to validate this. It found that genetic variants linked to autism may have been positively selected during human evolution because of their contribution to enhanced cognition. The study, based on a genome-wide association study of ASD and evolutionary gene selection, showed that inherited variants linked to ASD were found under positive selection in larger numbers than would have been expected by chance.

So, in caveman terms, people with ASD would have been the individuals within the social group or society who heavily contributed to technological and strategic advancements. Their diminished empathising would have been compensated for by other community members and familial groupings. Given the heritability of ASD traits and their continued presence to this day, it's a safe bet that groups with these individuals fared better than those that did not.

ASD: Prevalence In The Modern World & STEM Fields

The correlation between ASD and STEM subjects is an across-the-board trend that begins in the education system. Several studies have demonstrated that individuals with ASD attending higher education institutions are more likely than the general population to enrol in a STEM degree by quite some margin.

Which then carries over into the wider STEM workforce. But more than that, studies are beginning to highlight the types of individuals who thrive in these fields. A study conducted by the University of Cambridge in 2015 examined a relatively large sampling of individuals working in STEM-related jobs and found they had a higher-than-average Autism Spectrum Quotient score compared to the general population.

It's a fact that has had a clear demographic effect in the Silicon Valley-esque areas of the world. The 2012 Eindhoven study examined an area in the Netherlands where the tech and STEM-related industries are concentrated. It found that autism rates in schools were twice as high compared to other cities, strongly suggesting that the ASD attributes, at least in that localised region, are being positively selected for.

The TLDR: Is Autism Being Positively Selected For?

The idea that autism may have been and continues to be positively selected for in evolutionary terms is still a topic of ongoing research. However, the potential cognitive benefits associated with certain autism-related genes and the findings of studies on the topic push the balance of probability in favour of it being true.

Nevertheless, understanding the evolutionary roots of autism provides valuable insights into the diversity of human cognition and the potential advantages that neurodiversity may have conferred upon our species throughout history. So, perhaps there will come a time when the perception of ASD changes, and it's simply viewed as a different evolutionary strategy rather than a disorder.

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