Here is one interesting paper that is mentioned at Banerjee and Duflo's book 'Poor Economics':
The Potato's Contribution to Population and Urbanization: evidence from a historical experiment, by Nathan Nunn and Nancy Qian (2011). (working paper version)
Abstract:
We exploit regional variation in suitability for cultivating potatoes, together with time variation arising from their introduction to the Old World from the Americas, to estimate the impact of potatoes on Old World population and urbanization. Our results show that the introduction of the potato was responsible for a significant portion of the increase in population and urbanization observed during the eighteenth and nineteenth centuries. According to our most conservative estimates, the introduction of the potato accounts for approximately one-quarter of the growth in Old World population and urbanization between 1700 and 1900. Additional evidence from within-country comparisons of city populations and adult heights also confirms the cross-country findings.
Another loophole in your Theory, Sr. Malthus....