 The term “random drift” has both a narrow and a broad sense (Kimura 1964; Rice 2004; Millstein 2016). In the narrow sense, it refers to gene frequency changes that arise from the random sampling of gametes to form the offspring generation. (The point here is that organisms produce many more gametes than will ever make it into a fertilized zygote, and only half of a diploid organism’s genes are transmitted to each gamete). In the broader sense, drift refers to gene frequency changes arising from all stochastic factors, including for example random fluctuations in selection intensities, or in survival and mating success. The narrower sense of the term is used here.