Agreed, fascinating thesis but these types of big picture analysis are always as weak as their least reliable source of data. And as others have pointed out, labeling "pre colonial" Ireland as reliant on tubers makes me question their sources. I have the same problem with Pinker's "Better Angels of Our Nature" which seems hugely convincing until you check the footnotes and realize he's relying substantially on historical data from a single out of date and non peer reviewed source.