Titlepage to Thomas Malthus, An Essay on the Principle of Population, 1826.

50. Malthus, Thomas Robert, 1766-1834.
An Essay on the Principle of Population.  London: John Murray, 1826.

Thomas Malthus was a political economist who first published this book on population in 1798.  Malthus considered the relationship between human population growth and the growth of resources, and he discovered that while population tends to grow rapidly, resources increase much more slowly, so that, ultimately, there are going to be more humans than can survive.  Darwin, taking a break from working on his Beagle material, read Malthus in 1838.  In fact, he read this very edition, published in 1826.  Malthus was somewhat “in the air” in the 1830s; there had been a reform of the poor laws in 1834, and in the ensuing debate concerning the responsibility of a society towards its poor, Malthus was often invoked.  Although Malthus was concerned only with human population growth, Darwin read this work and immediately saw that its conclusions apply to populations in nature as well.  Animals breed much more rapidly than humans, and since natural resources do not increase at all, there must be a great “struggle for existence” among members of any species.  This was the missing piece in the puzzle for Darwin; he had already concluded that species change, but he did not know why they change.  After reading Malthus, he understood that only a few individuals will survive in each generation, and if they exhibit any variations, then their descendants will inherit those variations.  His concept of natural selection had now taken form.

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