  To see what these tasks are, consider the question, How do we decide whether a divergence from a long run relative frequency prediction about fitness differences is a matter of drift, a disconfirmation of the hypothesis of natural selection, or a reflection of a mismeasurement of fitness differences to begin with? Suppose we measure the fitness differences between population \(a\) and population \(b\) to be in the ratio of 7:3 (e.g., \(w_a = 1\), \(w_b = .428\)) and suppose further that in some generation, the actual offspring ratio is 5:5. There are four alternatives: (a) the fitness measure of 7:3 is right but there was drift—i.e., the initial conditions at this generation are unrepresentative of those which obtain in all relevant generations; (b) the fitness measure of 7:3 was incorrect and there was no drift; (c) both drift and wrong fitness measure or (d) the principle of natural selection is disconfirmed. Ignoring the fourth alternative, how do we discriminate among the first three of these?