This also served the ends of avoidance of conflict, social control within the group, and negotiating trade and territorial limits with other groups. High-level communication was also necessary to organize hunting and foraging expeditions to promote survival of the clan. They want to be around their family and friends. I don't mean an actual grossly evident neurological lesion. Obviously the structural changes in the brain would be subtle, as is evident from Margaret Bauman's neuropathologic studies.
Language is the most obvious.
After all, language is the quintessential tool for communication and building relationships. These all flow out of and, in fact, are intrinsic to the complex neurobiology of social cognition. An integral component of the social cognition system is the language subsystem which is markedly impaired in autism. Competency in language is uniquely basic to human nature and to the imperative of building and maintaining cooperative relationships that, in evolutionary terms, favored survival of the clan. The ability to generate subtly nuanced affect-loaded expressive language is severely impaired in autism.