A paper in Molecular Biology and Evolution has linked the evolution of the large human brain to autism. "we discovered that the most abundant type of neocortical neurons—layer 2/3 intratelencephalic excitatory neurons—has evolved exceptionally quickly in the human lineage compared to other apes. Surprisingly, this accelerated evolution was accompanied by the dramatic down-regulation of autism-associated genes, which was likely driven by polygenic positive selection specific to the human lineage." https://academic.oup.com/mbe/article/42/9/msaf189/8245036?login=false
From the discussion: " ... lower expression of ASD-linked genes in humans than in chimpanzees increases risk for ASD in the human lineage. Overall, our analysis suggests that natural selection on gene expression may have increased the prevalence of ASD."
Essentially, it is saying that autism is a by-product of us not being apes (except in the taxonomic sense), but being human.
