The Pleistocene epoch saw the extinctions of numerous preominantly larger species, many of which occurred during the transition to the Holocene epoch in what is termed the Holocene extinction event. Among the main causes hypothesized by paleontologists are the spread of disease, natural climate change, and overkill by humans, which appeared during this epoch. A variant of this last possibility is the second-order predation hypothesis, which focuses more on the indirect damage caused by overcompetition with nonhuman predators.