Potatoes caused urbanization

I've been meaning to link to this Chris Blattman post on a new paper:

... Old World regions that were suitable for potato cultivation experienced disproportionately faster population and urbanization growth after the introduction of potatoes.

... our baseline estimates suggest that the potato accounts for 12% of the increase in population, 22% of the increase in population growth, 47% of the increase in urbanization, and 50% of the increase in urbanization growth.

My impression was that potatoes were the highest-efficiency crop in terms of food energy (i.e. calories), but not particularly nutritious. But I was wrong:

Humans can subsist healthily on a diet of potatoes, supplemented with only milk or butter, which contain the two vitamins not provided for by potatoes, vitamins A and D. …This, in fact, was the typical Irish diet, which although monotonous, was able to provide sufficient amounts of all vitamins and nutrients.

I guess what I was remembering (I think from Jared Diamond's Guns, Germs and Steel) was that potatoes are low in protein (despite their micronutritional excellence). Still, I will think more positively of potatoes from now on.