To model the impact of dementia on past societies.
We consider multiple lines of evidence indicating elderly individuals to have been more common throughout the past than is frequently accepted. We then apply known dementia incidence/prevalence rates to plausible assumptions of past population structures to suggest prevalence in the past.
Dementia prevalence in premodern societies is likely to have been around 5% of the rate seen in modern, developed countries but with a total past incidence running into billions.
Dementia is often seen as a "modern" challenge that humans have not had to contend with before. We argue that this condition has had considerably greater effects than previously envisaged and is a challenge that humans have already withstood successfully, on one hand at a lower incidence but on the other without the considerable clinical, technological, and social advances that have been made in recent times.