 Extensionist theories are clearly less ontologically parsimonious than Dispersal Theories, since the former are committed to extra entities such as land bridges or movable tectonic plates. Moreover, Extensionist theories were (given the evidence then available) not manifestly superior in other respects. Darwin was an early critic of Extensionist theories, arguing that they went beyond the “legitimate deductions of science.” Another critic of Extensionist theories pointed to their “dependence on ad hoc hypotheses, such as land bridges and continental extensions of vast extent, to meet each new distributional anomaly” (Fichman 1977, p. 62) The debate over the more parsimonious Dispersal theories centered on whether the mechanism of dispersal is sufficient on its own to explain the known facts about species distribution, without postulating any extra geographical or tectonic entities.