The cause of megafaunal extinctions at the end of the last glaciation has been hotly debated during the last few decades, most recently at the global scale. In North America and elsewhere the debate centers on whether or not human hunters, who seemingly first entered the continent during the extinction period, caused the extinctions through over-hunting. An alternative explanation is that climate change during the terminal Pleistocene radically modified existing habitats and this caused the extinctions. Huston's (1979, 1994) dynamic equilibrium model (DEM) of community species richness provides a theoretical context for explanations of the extinctions in North America and highlights life history characteristics of extinct mammals. These life history traits and associated phenotypes are a seldom-explored line of evidence concerning the causes of the extinctions. In light of life history traits, environmental disturbance is implicated as the proximate cause of the extinctions, but the DEM does not preclude overkill as a contributing cause in North America.