This article uses such a broad definition of pre-colonial times. When exactly is that? I don't believe India was almost empty around 1400 AD. Quite contrary, given that there were already well established empires at that time.

Not hardly, by that time, Muslim invaders were half-way through 4 centuries of slaughtering 100 million Hindus (and I'm sure Sikh and Janes), and were hardly depopulating the land. And, yeah, there was a lot of history of empires and such before the start of this in the 13th Century.

And why is most of Europe except Ireland and Spain left out of the maps ? That alone suggests they could be cherry-picking the data.

Turnips and beets are roots too.

Ireland's myths and legends all revolve around cattle, and cattle - milk, specifically - was the primary source of food before potatoes, along with some grain and vegetables:

http://www.bonappetit.com/trends/article/what-the-irish-ate-...

Great article, I'm a little skeptical about the sourcing though. Most of the information seems to come from general literature (as opposed to something more objective, like say taxation records). What people choose to write about isn't necessarily what's most common in practice. For example a visitor from France would probably be more likely to write about some strange kind of cheese he's never seen before than the bread that looks more or less similar to what he's been eating everyday.

I don't doubt the importance of dairy but I doubt it accounted for the majority of people's calorie intake.

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hugely convincing until you check the footnotes and realize he's relying substantially on historical data from a single out of date and non peer reviewed source.

Do we have good information on what the crop distributions were in Ireland prior to 1492 (I assume that's how they define "pre-colonial") ? I wonder how this could really be determined anywhere. I wouldn't think there would be enough archaeological evidence to determine this with much accuracy and it seems unlikely written records from that period would have given sufficient detail either.

They actually have a pretty good idea of what they ate. Interesting article on it here:

http://www.ravensgard.org/prdunham/irishfood.html

The TLDR of their diet is "mostly pottage and soups, heavy on meat and dairy. Some oats and barley were grown, but a lot of that ended up being made into alcoholic beverages."

Alcoholic beverages have the advantage of making contaminated water drinkable without losing much in the way of calories in the original grain. A really clever solution to a problem of how to avoid dysentery when your water supply is not safe to drink.

What about China? Most of it looks like "large chiefdoms".