A new study in Molecular Biology and Evolution links autism to the same evolutionary changes that helped humans become highly intelligent. Researchers found that neurons in the brain’s outer layer, called L2/3 IT neurons, evolved much faster in humans than in other apes. Many of these rapid changes occurred in genes linked to Autism Spectrum Disorder (ASD). Natural selection shaped these autism-linked genes. This suggests they played a role in creating unique human cognitive abilities, including advanced reasoning and problem-solving skills.
These neurons are central to understanding both intelligence and neurodiversity. Today, autism affects about one in 100 children worldwide, and in the United States, one in 31 children is diagnosed. From an evolutionary perspective, autism and schizophrenia appear to be uniquely human. Behaviors such as differences in speech, language, and social interaction rarely occur in other primates, highlighting traits that are specific to humans.
Advances in tools like single-cell RNA sequencing allow scientists to study brain cell diversity and genetic variation more clearly. The fast evolution of autism-linked genes may have slowed aspects of brain development in childhood. While these delays could be challenging early on, they allowed the brain more time to wire itself. This extended development supported complex thought, advanced communication, and sophisticated language skills.
Lead author Alexander L. Starr explained, “Some of the same genetic changes that make the human brain unique also made humans more neurodiverse.” The study frames autism as an evolutionary trade-off. Certain genetic changes increased the risk of neurodevelopmental disorders, yet the same changes also contributed to the intelligence and language abilities that define humanity.
