Chapter 11: The Darwin–Wallace Theory of Natural Selection

The Darwin–Wallace Theory of Natural Selection academic summary explores the foundational principles of evolution by natural selection, independently proposed by Charles Darwin and Alfred Russel Wallace. Central to their mechanism is the recognition that organisms tend toward geometric population increase while environmental resources remain limited, a concept derived from the writings of the Rev. Thomas Malthus on political economy and demography. This disparity inherently creates a struggle for existence (competition) which drives the evolutionary process. Because of natural, heritable variation within a population, certain individuals possess features better adapted to the available resources and environment, leading to differential reproduction where those best-suited leave more offspring for the next generation. Over continuous generations, this process, combined with hereditary variation and changing environments, results in the modification of existing characters or the establishment of new ones, potentially leading to the rise of a new species if reproductive isolation occurs. While the men agreed on the core mechanism, their theories were not identical; Darwin placed significant importance on artificial selection (selection involving human choice, demonstrated through examples like dog and pigeon breeding) as a means to understand natural selection, whereas Wallace was unconvinced of its utility and prioritized geographical isolation. Darwin also used the vastness of geological time—calculating an estimate of 300 million years—to demonstrate the plausibility of natural selection achieving far greater changes than artificial selection. Furthermore, Darwin developed the principle of divergence to explain how competition leads to the specialization and splitting of species. Darwin famously delayed publication of his theory for over two decades, partly due to the desire to accumulate extensive evidence and partly due to fear of public ridicule following the hostile reception of works like Vestiges of the Natural History of Creation. However, the unexpected arrival of Wallace's manuscript describing the same theory in 1858 prompted Darwin's friends, Lyell and Hooker, to arrange a joint communication to the Linnaean Society to ensure Darwin received credit for his prior work.