 A final suite of philosophical issues surrounding population genetics concerns causation. Evolutionary biology is standardly thought of as a science that yields causal explanations: it tells us the causes of particular evolutionary phenomena (Okasha 2009, Otsuka 2016a). This causal dimension to evolutionary explanations is echoed in population genetics, where selection, mutation, migration and random drift are often described as causes, or ‘forces’, that lead to gene frequency change (Sober 1984). The basis for this way of speaking is obvious enough. If the frequency of allele \(A\) in a population increases from one generation to another, and if the population obeys the rules of Mendelian inheritance, then as a matter of logic one of three things must have happened: (I) migrants bearing allele \(A\) entered the population (II); there was mutation to allele \(A\) from another allele; (III) the average number of descendants left by each copy of \(A\) in the parental generation exceeded the average for all genes. It is straightforward to verify that if none of (I)–(III) occurred, then the frequency of allele \(A\) would have been unchanged. Note that case (III) covers both selection and random drift, depending on whether copies of \(A\) left more descendants than average by chance, or because of some systematic effect of \(A\) on organismic fitness.