Study suggests human evolution may explain higher rates of autism

A new study published in Molecular Biology and Evolution by Oxford University Press suggests that the relatively high prevalence of Autism Spectrum Disorder (ASD) in humans may be linked to evolutionary changes in the human brain, Caliber.Az reports via foreign media.

Autism affects roughly one in 31 children in the United States, or about 3.2%, while global estimates from the World Health Organization suggest that around one in 100 children have the condition. Scientists have long suspected that disorders such as autism and schizophrenia are largely unique to humans, given that behaviors associated with these conditions—particularly advanced cognitive traits like speech and comprehension—are rare in non-human primates.

Advances in single-cell RNA sequencing have allowed researchers to identify specific neuronal cell types across the mammalian brain. By comparing large-scale datasets from humans and other mammals, researchers discovered that some brain cell types evolved much faster in humans than in other species.

The study focused on L2/3 IT neurons, the most abundant type of outer-layer neurons in the human brain. These neurons showed accelerated evolution in humans compared to other apes. The researchers also found dramatic changes in genes associated with autism in these same neurons, suggesting that natural selection played a role in shaping these traits in humans.

Lead author Alexander L. Starr explained that while the findings indicate natural selection acted on autism-linked genes, the exact fitness benefits to early humans remain unclear. Researchers speculate that some of these genes may have contributed to slower postnatal brain development—a hallmark of human childhood—and potentially increased capacities for language and complex thought.

“Some of the same genetic changes that make the human brain unique also made humans more neurodiverse,” Starr said.

The study adds to a growing understanding of how human-specific brain evolution may underlie cognitive diversity, including susceptibility to conditions such as autism and schizophrenia. It also highlights how traits often considered “disorders” today may have had adaptive value in the evolutionary past.

By Vugar Khalilov