Pleistocene Overkill Hypothesis

The Pleistocene overkill hy­pothesis has for decades been championed by Paul Martin of the Uni­versity of Arizona. It is pointed out that Pleistocene vertebrates survived several periods of climatic change during the Pleistocene, yet the time of the major extinction came at the end of the Pleistocene. Martin's hypothesis suggests that the extinction follows the chronology of the spread of humans and their development as hunters of big game.

Martin reasons that when humans reached North America by the way of the land bridge that connected Siberia and Alaska they found herds of animals that were very vulnerable to human predation because they had never been confronted by humans before. Moreover, the in­vading humans had become skilled at hunting animals that were afraid of them. Thus, humans are thought to have spread rapidly through North America to the tip of South America, killing off the large herbivo­rous mammals as they went, in what has been termed a "Blitzkrieg."

Opponents to the overkill hypothesis point out that human kill sites are known from only a relatively few places and that human popula­tions were too small at the time to have caused such a mass extinction. It is an intriguing hypothesis, however, for otherwise it is difficult to explain why so few of the smaller vertebrates became extinct. If one considers the reptiles of the Pleistocene, for instance, the only significant extinction that took place was that of the giant tortoises; and these large reptiles would have been extremely vulnerable to human predation. In fact, a giant Pleistocene tortoise that had been cooked over a fire and had either been killed by a wooden spear or manipu­lated over the fire by the spear was found in a sinkhole in southwestern Florida.

The Pleistocene climatic equability hypothesis states that the climate in North America south of the glaciers must have been more equable than today with cooler summers and milder winters. The logical assumption is that the mild summers allow for the presence of the northern animals found in North American Pleistocene sites and that mild winters allow for the presence of the southern animals.

Questionnaire:

• Explain about the Pleistocene overkill hy­pothesis?