Where Autism Comes From

TL;DR: It's genetic. That's mostly what we know so far — research is ongoing — and the “epidemic” framing is alarmism.

Compelling evidence shows that genetic factors contribute significantly to the risk of developing ASD, as demonstrated by the higher concordance rates between identical twins compared to fraternal twins. Although the specific triggers for gene activation related to brain development are still being studied, it is clear that these genetic factors can lead to diverse neurological development. It is essential to emphasize that there is no epidemic of ASD. Current research has not identified toxins or environmental factors as causal contributors.

Because Autism is a spectrum, there is also a spectrum of associated factors, including advanced paternal age and certain epilepsy medications.

So why does it look like an epidemic?

Autism has always been prevalent; diagnostic tools simply weren't precise enough to detect it. Improved awareness following IDEA, the DSM, and cultural phenomena like Temple Grandin and Rain Man increased surveillance for Autism. There has also been a decline in diagnoses of intellectual disabilities, learning disabilities, and emotional disturbances in favor of ASD — a phenomenon known as diagnostic substitution.

Centers for Disease Control and Prevention. (2024). About autism spectrum disorder. U.S. Department of Health and Human Services. https://www.cdc.gov/autism/about/

Tick, B., Bolton, P., Happé, F., Rutter, M., & Rijsdijk, F. (2016). Heritability of autism spectrum disorders: A meta-analysis of twin studies. Journal of Child Psychology and Psychiatry, 57(5), 585–595. https://doi.org/10.1111/jcpp.12499