In an earlier post I mentioned that Malthus didn't count on Potatoes. Actually, Prof. John R. Weeks (who writes an excellent blog, by the way), has pointed me an excerpt of Malthus' book where he acknowledges the role of potatoes on the population growth of Ireland during the 17th Century and the first half of the 18th Century (before the Irish Potato Famine). Thank you John!
The details of the population of Ireland are but little known. I shall only observe therefore, that the extended use of potatoes has allowed of a very rapid increase of it during the last century. But the cheapness of this nourishing root, and the small piece of ground which, under this kind of cultivation, will in average years produce the food for a family, joined to the ignorance and depressed state of the people, which have prompted them to follow their inclinations with no other prospect than an immediate bare subsistence, have encouraged marriage to such a degree, that the population is pushed much beyond the industry and present resources of the country; and the consequence naturally is, that the lower classes of people are in the most impoverished and miserable state. The checks to the population are of course chiefly of the positive kind, and arise from the diseases occasioned by squalid poverty, by damp and wretched cabins, by bad and insufficient clothing, and occasional want. To these positive checks have, of late years, been added the vice and misery of intestine commotion, of civil war, and of martial law. (Malthus, An Essay on the Principle of Population, II.X.38)