Noah Berlatsky writes: Chance is an uncomfortable thing. So Curtis Johnson argues in Darwin’s Dice: The Idea of Chance in the Thought of Charles Darwin, and he makes a compelling case. The central controversy, and the central innovation, in Darwin’s work is not the theory of natural selection itself, according to Johnson, but Darwin’s more basic, and more innovative, turn to randomness as a way to explain natural phenomena. This application of randomness was so controversial, Johnson argues, that Darwin tried to cover it up, replacing words like “accident” and “chance” with terms like “spontaneous variation” in later editions of his work. Nonetheless, the terminological shift was cosmetic: Randomness remained, and still remains, the disturbing center of Darwin’s theories.
Johnson, a political theorist at Lewis & Clark College, explains that there are two basic kinds of chance in Darwin’s thought. The first—most familiar and least disconcerting—is chance as probability. According to the theory of natural selection, individuals with advantageous adaptations are most likely to survive. A giraffe with a longer neck has a better shot of reaching those lofty leaves and living to munch another day; a polar bear blessed with a warmer coat has a higher probability of surviving a frigid winter than one with less hair. The long-necked giraffe may not always win—it may, for example, be pulverized by a meteor before it can pass on its long-necked genes. But over time, the odds will go its way. There is randomness here, but it is controlled and predictable: It works in accordance with a rule. Natural selection makes sense.
The second kind of chance in Darwin’s work, though, is more mysterious. For natural selection to work, you need to have a range of traits to select among. That range is provided by individual variation, the fact that two different animals (whether giraffe or bear) are different from each other. Some giraffes have longer necks than others. Some bears have thicker fur than others. Why should this be? Darwin’s answer was chance. [Continue reading…]