On playgrounds, in classrooms, and across families worldwide, autism spectrum disorder (ASD) is no longer a hidden or rare phenomenon. One in 31 children in the United States is diagnosed with autism, and the World Health Organization estimates one in 100 children globally are on the spectrum. But why humans, specifically? Why does autism appear so frequently in our species and yet is almost absent in other primates?
A new study in Molecular Biology and Evolution suggests the answer may lie in our very origins. Researchers argue that autism is not simply a medical condition, but a reflection of the evolutionary gamble that shaped the modern human brain.
A Brain Unlike Any Other
For decades, scientists have noted that disorders like autism and schizophrenia seem uniquely human. The traits tied to these conditions—such as speech, abstract thinking, and social cognition—are also the hallmarks of what makes our species distinct. Unlike chimpanzees or gorillas, humans possess not only the ability to communicate in complex language but also to imagine, plan, and reason on an unprecedented scale.
Behind these capabilities lies a striking biological truth: the human brain is home to an extraordinary diversity of neuronal cell types. Thanks to single-cell RNA sequencing, researchers have been able to map these neurons in unprecedented detail. What they’ve found is that certain brain cells, particularly L2/3 IT neurons in the outer cortex, have evolved far more rapidly in humans than in our closest relatives.
The Autism Connection
This rapid evolution, it turns out, is not random. It aligns closely with genes that modern science has already linked to autism. The study’s lead author, Alexander L. Starr, and his team uncovered that these autism-associated genes underwent dramatic changes specifically in humans, driven by natural selection.
But here’s the paradox: if autism is linked to genetic mutations, why would natural selection preserve and even accelerate them? The researchers propose a daring answer—these genetic shifts may have offered early humans unique advantages.
Evolution’s Trade-Offs
One theory is that genes tied to autism slowed postnatal brain development. While this delay may sound like a weakness, it could have provided a critical edge. A slower-developing brain allowed children more time for environmental learning, social interaction, and language acquisition—skills central to human survival and cooperation.
Speech, too, seems woven into this puzzle. Autism often affects communication, but the very genes linked to it might have enabled humans to develop language in the first place. In other words, the price of our linguistic brilliance may have been greater neurodiversity.
The Bigger Picture of Neurodiversity
Seen through this evolutionary lens, autism is not an anomaly but part of the human story. Some of the same genetic changes that gave rise to imagination, culture, and science may also explain why autism is relatively common today.
The study doesn’t pretend to offer all the answers—it remains unclear exactly why these traits improved survival for early humans. But the findings push us to rethink autism not merely as a disorder, but as an echo of the evolutionary process that made our species extraordinary.
As Starr puts it, “Some of the same genetic changes that make the human brain unique also made humans more neurodiverse.”
In the end, autism may be more than a challenge modern families face—it may be a reminder of the evolutionary forces that carved out the complexity of being human.
