There is some genetic evidence that autism may be linked to atavistic Neanderthal gene variants cropping up in modern humans. One of the symptoms of autism is having difficulties in social interactions, suggesting that Neanderthals might have been similarly disadvantaged. This is one reason, perhaps, why they lived in smaller social units than modern humans—and why they could not compete when we arrived with our bigger and more cooperative groups.
Autism - Neanderthals?
