Complexity_ A Guided Tour - Melanie Mitchell [37]
Thomas Malthus’s Essay on the Principle of Population (1798) drew Darwin’s attention to the fact that population growth leads to competition for food and other resources. Malthus’s essay was about human population growth, but Darwin would adapt these ideas to explain the evolution of all living organisms via a continual “struggle for existence.”
Darwin also read Adam Smith’s free-market manifesto, The Wealth of Nations (1776). This book exposed him to Smith’s notion of the invisible hand in economics, whereby a collection of individuals acting in their own self-interest produces maximum benefit for the entire community.
From his own observations in South America and elsewhere, Darwin was acutely struck by the tremendous variation among living beings and by the apparent adaptation of different species to their environments. One of his most famous examples is the finches of the Galápagos Islands, 600 miles off the coast of Ecuador. Darwin observed that different species of these small birds, although otherwise quite similar to one another, have wide variations in beak size and shape. Darwin was eventually able to show that different species of finches had common ancestors who had evidently migrated to individual islands in the Galápagos chain. He also showed that the type of beak was adapted to the individual species’ food sources, which differed among the islands. Darwin hypothesized that the geographical isolation imposed by the different islands, as well as the local environmental conditions, led to the evolution of these many different species from a small number of ancestors.
We can imagine Darwin with these ideas swirling in his head during his voyage and afterward, back in England, trying to make sense of the data he had collected. Gradual change over long periods can produce very large effects. Population growth combined with limited resources creates a struggle for existence. Collections of individuals acting in self-interested ways produce global benefit. Life seems to allow almost infinite variation, and a species’ particular traits seem designed for the very environment in which the species lives. Species branch out from common ancestors.
Over the years, it all came together in his mind as a coherent theory. Individual organisms have more offspring than can survive, given limited food resources. The offspring are not exact copies of the parents but have some small amount of random variation in their traits. The traits that allow some offspring to survive and reproduce will be passed on to further offspring, thus spreading in the population. Very gradually, through reproduction with random variation and individual struggles for existence, new species will be formed with traits ideally adapted to their environments. Darwin called this process evolution by natural selection.
For years after the development of his theories, Darwin shared his ideas with only a few people (Charles Lyell and some others). In part, his reticence was due to a desire for additional data to bolster his conclusions, but also contributing was a deep concern that his theories would bring unhappiness to religious people, in particular to his own wife, who was deeply religious. Having once considered becoming a country parson himself, he expressed discomfort with his main conclusion: “I am almost convinced (quite contrary to the opinion I started with) that species are not (it is like confessing a murder) immutable.”
However, Darwin’s notebooks of the time also revealed his understanding of the philosophical implications of his work for the status of humans. He wrote, “Plato…says in Phaedo that our ‘necessary ideas’ arise from the preexistence of the soul, are not derivable from experience—read monkeys for preexistence.”
Competition is not only the centerpiece of evolution, but is also a great motivator in science itself. Darwin’s hesitation to publish his work quickly melted away when he discovered that he was about to be scooped. In 1858,