New Research Links Human Evolution to Rising Autism Rates

Recent research indicates that the evolution of the human brain may play a significant role in the increasing rates of autism spectrum disorder (ASD). A study led by Alexander L. Starr suggests that some genetic changes that distinguish the human brain from those of other mammals could also contribute to greater neurodiversity, including higher autism rates.

According to the Centers for Disease Control and Prevention (CDC), approximately one in 31 children in the United States is diagnosed with autism, equating to about 3.2 percent of the population. Globally, the World Health Organization (WHO) estimates that ASD affects one in 100 children. The condition is characterized by challenges in social communication, restricted interests, and repetitive behaviors.

Unique Traits of Human Neurology

Unlike other neurological conditions observed in animals, autism and schizophrenia appear to be primarily human phenomena. These conditions are believed to be linked to advanced traits such as speech production and comprehension, which are either exclusive to humans or significantly more developed than in other primates.

Recent advancements in single-cell RNA sequencing have enabled scientists to identify a remarkable variety of brain cell types. At the same time, large-scale genetic studies have shown significant changes in the human brain that are not found in other mammals. Researchers have analyzed brain samples from various species, discovering that the outer-layer neurons, specifically the L2/3 IT neurons, evolved more rapidly in humans compared to other apes. This rapid evolution aligns with notable changes in genes associated with autism, likely influenced by natural selection factors unique to humans.

The Evolutionary Benefit of Genetic Changes

While the findings suggest that evolutionary pressures may have impacted autism-related genes, the specific advantages for early humans are still unclear. The research team noted that many of these genes are related to developmental delays, which could explain the slower postnatal brain growth seen in humans compared to chimpanzees.

Additionally, the unique human capacity for language and speech, often affected by conditions like autism and schizophrenia, might be tied to these genetic changes. One hypothesis is that the evolution of genes linked to autism may have delayed early brain development or enhanced language capabilities. This extended developmental period could have provided an evolutionary advantage by allowing for more complex reasoning skills to emerge during childhood.

The study, titled “A general principle of neuronal evolution reveals a human-accelerated neuron type potentially underlying the high prevalence of autism in humans,” is set to be published in Molecular Biology and Evolution in March 2025.

As researchers continue to explore the connections between human evolution and neurodiversity, these insights may reshape our understanding of autism and its prevalence in modern society.