 As an illustrative example, consider punctuated equilibrium, which has certainty been articulated in many and varying ways. The two initial publications by Eldredge (1971) and Eldredge and Gould (1972) are undoubtedly the founding ones, but there are other crucial moments in the development of the theory (e.g., Gould &amp; Eldredge 1977, 1983, 1986, 1993; Eldredge &amp; Gould 1988; Gould 2002). At times the shifting nature of PE has been a target of criticism (e.g., Levinton 1986; Coyne &amp; Charlesworth 1997; see Eckhardt 1986 for a particularly entertaining visit from “the shade of Francis Galton”).