When the first United States census was completed in 1790, the British scholar Thomas Malthus supposed that the remarkable recent growth of the American population, which had doubled in the previous 25 years, was a consequence of ample food supply and the active encouragement of marriages, neither of which characterized Europe at the time. In his 1798 volume An Essay on the Principle of Population, Malthus argued that a similar periodic doubling of population in the British Isles, on the other hand, would outstrip the more slowly increasing food supply in 50 years and lead to starvation. That is, increasing the number of births per year would eventually result in an increased number of deaths because the amount of food the land could produce was limited. This view of the human condition influenced the thinking of Charles Darwin, who as an inquisitive student read the most exciting works of the day. Darwin realized that the tension between population growth and resource limitation applies to all species, leading to a struggle for existence that results in adaptations that enhance survival (Chapter 21).

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