Science

If you see autism as an inherently useful trait to have in the small communities in which we used to live, that would explain why these clusters have persisted. The genetic traits that confer benefits to the individual are passed along to descendants, and the associated variations just go along for the ride.

For instance, one allele for sickle cell anemia provides protection against malaria; two alleles make you very sick, but only 1 in 4 people get both alleles, so 3 people survive malaria for every 1 person who dies from the condition.