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Return Home Development of the Theory Darwin set out in 1831 an aspiring naturalist headed for the clergy but he stepped off the Beagle in 1836 a different man. Before the voyage he had read William Paleys major works including A View of the Evidences of Christianity which was on the exams at Cambridge and Natural Theology. In his autobiography Darwin wrote The logic of this book Evidences and as I may add of his Natural Theology gave me as much delight as did Euclid. The careful study of these works without attempting to learn any part by rote was the only part of the academical course which as I then felt and as I still believe was of the least use to me in the education of my mind. I did not at that time trouble myself about Paleys premises and taking these on trust I was charmed and convinced by the long line of argumentation. In Natural Theology Paley invoked his famous watchmaker analogy any reasonable person upon finding a watch and seeing its complex and intricate design would assume it had been made by a watchmaker. In short design implies a designer. But by the time he returned Darwin was skeptical of such explanations. The question in Darwins mind was not do species evolve but how. Evolution itself was not a new idea. In 1809 Jean-Baptiste Lamarck had proposed that species changed by an underlying law of progress and the inheritance of acquired characteristics in his book Philosophie Zologique. Even Darwins own grandfather had written on the subject in Zoonomia 1794-1796 Erasmus Darwin had proposed that species adapt to their environment driven by lust hunger and danger an idea at least superficially similar to the theory of natural selection. But earlier theories were flawed or incomplete. Malthus and Population In September 1838 Darwin read An Essay on the Principle of Population by Thomas Malthus and a bell went off. Malthus argued that human population growth unless somehow checked would necessarily outstrip food production. Unchecked population growth according to Malthus would be exponential while the food supply could only grow arithmetically. Malthus was referring to human populations of coursehis objectives were socio-political not scientific. But Darwin quickly saw how the same principle could apply to the natural world. Far more offspring were born than could possibly survive because there simply wasnt enough food to go around. Individuals with a slight advantage would do better. Over a long period of time even the smallest advantage would prove decisive. Thanks to the new geology he had millions of years to work with. From the Brazilian rain forest to the Galpagos Islands Darwin had witnessed the considerable variation between individuals of the same species. He didnt know what caused such variations but he didnt need tohe theorized at a higher level. He contended that the struggle for existence acted upon the smallest differences however those differences came about. Forced to compete and to adapt to ever-changing environments which Darwin had also witnessed species evolved. In his autobiography Darwin wrote Here then I had at last got a theory by which to work. Marriage Family In 1839 Darwin married Emma Wedgwood his first cousin a practice not uncommon in Victorian England among the propertied 23