Just how did he get there? For starters, Darwin began his studies with the intent of becoming a doctor. He found that he didn't have the stomach for surgery, so he switched to theology. A country vicar was the future that young Darwin saw for himself even up until he set sail on the Beagle. But even so, it was the study of nature that captivated him. As Janet Browne recounts, he was especially interested in a man whose ideas Darwin would eventually make obsolete.
In particular Darwin engaged with the theological views of Archdeacon William Paley, initially as part of his syllabus and then as independent reading. Darwin was expected to be able to answer questions in the final examinations on Paley's Evidences of Christianity and Moral Philosophy. After he graduated, he read the last of Paley's trilogy, Natural Theology (1802), with its argument that the adaptation of living beings to their surroundings was so perfect that it proved the existence of God. How could such a perfect design have come about, stated Paley, except from the careful hands of a designer? If a watch were accidentally found on a path, we would be entirely justified in thinking that it had been constructed by a skilled craftsman according to some design or plan. Such intricate mechanisms do not suddenly appear out of nothing, like magic. They are made by a maker. So, Paley argued, the world about us must be considered in the same way as the watch.
Darwin was also influenced by Malthus' An Essay on the Principle of Population which stated that populations grow exponentially until they no longer have the resources to maintain themselves, then they are subject to competition, poverty, and decline. Another great influence was Lyell's Principles of Geology which stated that land forms were not always as they as today, but rather formed slowly through natural processes (such as erosion, etc.). Ironically, Lyell specifically made an exception for living things which--of course--were not subject to change in the same way.
Charles Darwin circa 1860--about the time he published Origin of Species
Now contrary to popular opinion, Darwin didn't come up with his theory while observing all the different forms on the Galapagos. While he did note the variation from island to island with interest, it wasn't until he got back home and started to study his logs and samples and then really think about them deeply that his theory began to form. And once it formed, he took his time to get it right. Twenty years passed between his first documented mention of the idea and the publishing of Origin. The reasons for the delay are often debated among scholars, but what is for sure is that when he did publish, every i was dotted and every t was crossed. "He examined the minutiae of nature" notes biologist and writer Olivia Judson in today's New York Times "but worked on grand themes."
Could plants from the mainland colonize a newly formed island? If so, they would need a way to get there. Could they survive in the ocean? To find out, he immersed seeds in salt water for weeks, then planted them to see how many could sprout. He reported, for example, that “an asparagus plant with ripe berries floated for 23 days, when dried it floated for 85 days, and the seeds afterwards germinated.” The Atlantic current moved at 33 nautical miles a day; he figured that would take a seed more than 1,300 miles in 42 days. Yes, seeds could travel by sea.
Here are the first couple paragraphs from chapter IV of Origin, where he begins to explain his notion of natural selection.
Be sure to check out the other Darwin Day posts at Blog for Darwin Carnival.
Now let me finish my Darwin Day post with a shout out to my favoritest and adorablest nephew, Rafael Darwin.