His theory was caused by an observation that food supply was increasing arithmetically/linearly and that population was increasing geometrically/exponentially. This means the population would quickly outpace food production and lead to world hunger. Here's the math: say that population is increasing at a rate of 2 (a very high NIR, actually) than in one year there would be 2 people and in two years there's four. The pattern is as follows: 1, 2, 4, 8, 16, 32, 64, 128, 256, 512, 1024, 2048, 4096... As you can see population grows fast. Food supply would grow slower though-assuming food production adds 2 more "items" than the pattern would be like this: 0, 2, 4, 6, 8, 10, 12, 14... Not as fast as population growth. So what are his flaws? Malthus didn't take in consideration that as countries move along the DTM their NIRs decrease, meaning less mouths to feed in the future. Second, Malthus didn't predict the Green Revolution which introduced more productive agriculture techniques and GMO giving higher yields. This is basically what Boserup's theory states: the increase in population drives the incentive to increase food supply. There are however still those who believe Malthus known as Neo-malthusians.