What is the Overkill Hypothesis
A basic assumption of the Pleistocene extinction, or “overkill” hypothesis, is that rates of human predation on numerous genera of megafauna exceeded prey replacement rates. Previous assessments of this hypothesis have often stressed the technological or organizational capabilities of Paleolithic hunters to harvest prey in sufficient numbers to threaten extinction. Optimal foraging models and ethnographic observations of modern hunters-gatherers provide a logical basis for assessing the feasibility of alternative reconstructions of Paleolithic hunting strategies as well as their compatibility with the concept of critically high rates of predation sufficient to cause extinction.
Quaternary extinction event - Wikipedia
For the overkill hypothesis to hold true, prehistoric humans must have killed off the megafauna very rapidly - within 1,000 years of arriving in a region. If the extinction happened more slowly than this, it wouldn't have been true overkill. More to the point, it may be impossible to pick apart all the interrelated factors (hunting, climate and competition) that would have played a part over a longer period.
Particularly hard hit were Australia and the Americas. In Australia, 15 of the continent's 16 genera of large mammals died out, North America lost 33 of 45 large-mammal genera, and in South America 46 of 58 such genera went extinct. In contrast, Europe lost only 7 of 23 such genera, and in Africa south of the Sahara only 2 of 44 died out. No completely satisfactory explanation exists, but two competing hypotheses are currently being debated. One hypothesis holds that rapid climatic changes at the end of the Pleistocene caused extinctions. The other hypothesis, called prehistoric overkill, holds that human hunters were responsible.
The Holocene epoch