 Walsh, Lewens, and Ariew (2002) provide a good entrée into understanding a mathematical approach to drift. They begin by acknowledging the historical uses of the term drift, identifying four: 1) a “Sewall Wright Effect”, 2) a “Hagedoorn Effect”, 3) “Indiscriminate Sampling”, and 4) “The Finiteness of Natural Populations” (with some of their characterizations not fully accurate; e.g., with the first, they conflate Sewall Wright’s Shifting Balance Model where drift plays a role with drift itself). They suggest that these phenomena are “disparate” although they acknowledge, citing Beatty (1984), that the first three can be understood in terms of sampling. But the fourth form, they assert, cannot. They describe the fourth phenomenon as follows: