Apparently its almost unheard of in some cultures to have any sort of back problems, even after decades of physical labor etc. The premise of the book is that the reason for this is that these people are using their spines and posture in a more natural fashion, which leverages the structure of the spine better, but we don't do it in the West as the result of a kind of cultural revolt against victorian era posture norms that took place in the 1920's
It's so obnoxious how people like you expect members contributing to the discussion to have perfect proof on hand or go digging. If that were the true standard, these discussions would be much thinner.
It's fine to ask, just don't be an asshole when a person doesn't have it; look it up yourself.
