Scientists have uncovered new evidence suggesting that autism may have it roots in how the human brain has evolved.
“Our results suggest that some of the same genetic changes that make the human brain unique also made humans more neurodiverse,” said the study’s lead author, Alexander L. Starr in a statement.
In the United States, around one in 31 children—about 3.2 percent—has been diagnosed with autism spectrum disorder, according to the Centers for Disease Control and Prevention (CDC).
Autism spectrum disorder is a complex developmental condition affecting roughly one in 100 children worldwide, according to The World Health Organization.
It involves persistent challenges with social communication, restricted interests and repetitive behavior.
Unlike other neurological conditions seen in animals, autism and schizophrenia appear to be largely unique to humans, likely because they involve traits such as speech production and comprehension that are either exclusive to or far more advanced in people than in other primates.
The Human Brain and Genetic Change
Recent advances in single-cell RNA sequencing have allowed scientists to identify an extraordinary diversity of brain cell types.
Alongside this, large-scale genetic studies have revealed sweeping changes in the human brain that are not seen in other mammals.
These genomic elements evolved rapidly in Homo sapiens despite remaining relatively stable throughout the rest of mammalian history.
By analyzing brain samples across different species, researchers found that the most common type of outer-layer neurons—known as L2/3 IT neurons—underwent especially fast evolution in humans compared to other apes.
Strikingly, this rapid shift coincided with major alterations in genes linked to autism—likely shaped by natural selection factors unique to the human species.
Why Did These Changes Occur?
Although the findings strongly point to evolutionary pressure acting on autism-associated genes, the evolutionary benefit to human ancestors remains uncertain.
The team behind the research noted that many of these genes are tied to developmental delay, which may have played a role in the slower pace of postnatal brain growth in humans compared to chimpanzees.
The unique human ability for speech and language—often impacted by autism and schizophrenia—may also be connected.
One possibility is that the evolution of autism-related genes slowed early brain development or expanded language capacity, extending the time window for learning and complex thought in childhood.
This extended development may have offered an evolutionary advantage by fostering more advanced reasoning skills.
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Reference
Starr, A. L., & Fraser, H. B. (2025). A general principle of neuronal evolution reveals a human-accelerated neuron type potentially underlying the high prevalence of autism in humans. Molecular Biology and Evolution. https://doi.org/10.1093/molbev/msaf177
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