RANDOM DRIFT: CHANCE AND EXPLANATION IN EVOLUTIONARY BIOLOGY
Johns Hopkins University
The central claim for which I argue in this dissertation is that there are important phenomena that occur by random drift that evolutionary biologists explain using a strategy I term “process explanation.” This claim puts me at odds with an influential view about the nature of explanation that I term “Hempelianism.” Hempelianism is the view that the scientific explanation of a particular event E requires (a) showing that E was to be expected, or indicating the degree to which it would have been rational to expect E’s occurrence; and (b) laws of nature. My central claim entails that both (a) and (b) are false. A process explanation consists of a narrative describing events causally relevant to the event to be explained. These narratives need not contain laws, show that the event to explained ought to have been expected, or indicate the degree to which it would have been rational to expect the event. My position about random drift also puts me at odds with evolutionists who, influenced by Hempelianism, claim that only natural selection can explain evolution. In my argument, I articulate the strategy of process explanation and defend it against Hempelian critics; describe a mechanism of random drift known as “indiscriminate ii sampling;” and describe process explanations of phenomena of drift that occur by indiscriminate sampling.