The Struggle for Existence: 1859 & Today
Walsh, Joseph A., The American Biology Teacher
A useful teaching technique is to have students summarize a major topic in ten words or less. These pithy nuggets can be listed for the entire class to critique, with the resulting conversation helping the students recognize flaws in their thinking. One of the best submitted ten-word summaries of the work of Charles Darwin is: "Heritable variation, differential reproduction, and time yields modified descent, naturally." Phenotypic variation was widely accepted in Darwin's time. Heredity, or "like breeds like," was also common knowledge, although the exact genetic mechanisms were not. Reading Lyell while on the Beagle gave Darwin a sense of deep time. Malthus had made the observation that unchecked reproduction and survival would generate a population that would outstrip resources, resulting in competition for these resources. Reading Malthus helped Darwin realize that differential reproduction, or what in Chapter 3 of On the Origin of Species he called the "struggle for existence," gave descent with modification (i.e., evolution) the mechanism of natural selection. The "naturally" refers to the materialistic nature of the changes in species over time.
The theory that natural selection is the key to adaptive evolution, and the reasoning for his conclusions, were Darwin's contributions to science. However, only half of Americans accept the fact of evolution as true (Gallup, 2008). Some conceptual barriers are easily overcome. Students today, as in Darwin's time, need only look at their canine pets to see phenotypic variation. They look at their classmates and the parents of their classmates to see heritable differences. Students shown pictures of the stratification within the Grand Canyon and the mathematical logic of nuclear decay generally accept the vast depth of geologic time. Life's existential struggle is less apparent to students, however, for three reasons.
First, popular books suggest that modern American children suffer from "Nature Deficit Disorder" brought on by children's lack of exposure to unstructured play in unstructured natural environments (Louv, 2005). They play on manicured lawns and playgrounds, but never see the chaotic struggles of self-interested predators and prey that Darwin recognized as the organizing principle for non-directed descent with modification, simply Adam Smith's economic "invisible hand" applied to nature (Smith 2008). Second, children in developed countries don't feel that they themselves are in a struggle for existence. Humans have never seen the microscopic predators stalking them, and our students live in a country where these predators have largely been tamed. Vaccines, water sanitation, improved waste disposal, abundant food, antibiotics, and scientifically-based health care all contribute to students' health and security. These first two reasons, isolation from nature and isolation from predators, are modern developments that should be made explicit to students, and contrasted to the Victorian England of Darwin. In order to give students an appreciation for the historical context of Darwin's discoveries, we can give an overview of Darwin's experiences as a spectator of nature, and as a man who grieved over family members lost to microbial disease.
Darwin is often pictured in textbooks as an old graybeard, but he began his Beagle adventure at the age of 22, not much older than our students. He had always been an amateur naturalist, and though he was hired on as the captain's gentleman companion, he quickly became the de facto ship's naturalist. His trip brought him into contact with exotic examples of the struggle for existence. He wrote about non-human struggles in Chapter 2 of The Voyage of the Beagle:
Certain wasp-like insects, which construct in the corners of the verandahs clay cells for their larve, are very numerous in the neighbourhood of Rio. These cells they stuff full of dead and dying spiders and caterpillars . …