For years and years, the media and media driven scholars have advanced the notion that primitive societies were somehow better than our own, more friendly, more tolerant, more charitable, more in tune with Nature's harmony. Of course, it was all BS. With very few exceptions, the farther back one goes in evolutionary history, the more savage and cruel societies were. Those alleged societies of South and Central America were not only savage and cruel, but, very likely, insane, as well. One doesn't need a degree in psychology or psychiatry to read the mindset behind the stone carvings they have left us. Uncovering their blood-thirsty sacrifices only adds to the case against their sanity. Add to that a diet of high carbohydrates for generation after generation, and one is safe in concluding that both their beliefs and their behaviors were symptoms of a terminal disease.
You bringing up the high carb diet got me thinking, I wonder if it's possible that ergotism was a factor.
http://en.wikipedia.org/wiki/Ergotism