Is ADHD actually a neurodegenerative disorder, or is it a natural human variation? How do we know that ADHD hasn't always been a substantial portion of the popu

Is ADHD actually a neurodegenerative disorder, or is it a natural human variation? How do we know that ADHD hasn't always been a substantial portion of the population, and we've only recognized it once we developed modern civilization post-agrarian revolution where kids need to sit in classrooms for 6 hours a day and homework for 1-2 hrs a day. Or that mind numbing repetitive jobs were not something hunter-gathers evolved for? I'd believe that these chemicals may be causing brain changes, but I am highly skeptical of the claims there's been massive increase in autism and ADHD. Would a hunter-gatherer or nomadic society even recognize ADHD as abnormal? Or high functioning autism for that matter?