Darwin’s Theory of Natural Selection

On the Origin of Species by Means of Natural Selection was over twenty years in its formulation and was based on a number of disparate sources and observations that Charles Darwin had the genius to integrate. While sailing on the HMS Beagle (1831–1835), he read Principles of Geology, wherein Charles Lyell proposed that the fossils embedded in rock were imprints of living beings millions of years old that no longer inhabited the earth nor resembled extant beings. In 1838, Darwin read Thomas Malthus’s An Essay on the Principle of Population, in which Malthus postulated that the rate of growth of the population was far exceeding the food supply and that, if unchecked, would have catastrophic consequences. Darwin also considered the practice of farmers who selected their best animal stock for breeding (artificial selection). The fourteen finches he found on the Galápagos Islands were similar in all respects, with the exception of the size and shape of their beaks, which were adapted to the available supply of food on their island.

Darwin was not the first to conceive of evolution, but the others lacked a coherent theory to explain its occurrence. His theory was based on natural selection. In nature, there is competition within the species for the limited resources. Those living beings that have the most favorable traits that are best adapted to their environments are most likely to survive and reproduce and pass their favorable traits on to offspring. Thus, over many generations, the species that has arisen from a common ancestor “descends with modifications.”

An 1869 photograph of Charles Darwin taken by Julia Margaret Cameron (1815–1879), who was known for her photographs of British celebrities.

In the 1840s, Darwin sketched the outline of his natural selection theory in an essay. Anticipating a storm of protest to greet his anti-Creation theory, he hesitated to go public but, over the next decade, continued to gather additional evidence to bolster it. In 1858, Darwin learned that a fellow naturalist, Alfred Russel Wallace, had independently developed a theory of natural selection that was strikingly similar to his own. Darwin rapidly completed his book, Origin of Species, which appeared in 1859 and proved to be a runaway best seller and a classic in scientific literature.