History

One of the most remarkable events of the Pleistocene Age was the extinctions of many species of large herbivores, some carnivorous mammals, several bird species, and a few plant species. This age saw the extinction of as many as 35 genera of large mammals in North America. South America and Europe too lost many species of herbivores while Africa and Asia lost fewer species compared to the rest of the continents. Although most of the extinct animals were wiped off between 12,000 and 10,000 years, the extinctions only happened as late as 4,000 years ago in regions including the Wangel Island in the Arctic Ocean (Grayson, 2007). Theorists have advanced a wide variety of ideas in their attempts to account for the massive and widespread losses of plant and animal species which occurred over a short period of time (Scott, 2009). One of the hypotheses advanced to explain the extinctions is the prehistoric overkill hypothesis.

The central idea of the overkill hypothesis is that human predation of the large herbivores was the cause of the Pleistocene extinction. Proponents of this hypothesis have advanced what is regarded as a causal link between the extinction and the appearance of human life. Paul Martin and other proponents of the overkill hypothesis argue that the extinction, which was most intense in North America, followed the appearance of human beings in the region.

About 15,000 years ago, North America was inhabited by a large population of herbivorous and carnivorous species. The ancestors of Native Americans landed on the continent about 14, 000 years ago to find the large population of herbivores. These animal species had not encountered human beings previously and did not perceive them as a threat. The Native Indian population took advantage of the fact that the animals did not recognize them as predators, and hunted the large herbivores in large numbers. Predictably, the Native Indians developed a preference for large herbivores such as the giant bison, mammoths, buffaloes and ground sloths, killing them to the point of extinction (AMNH, n.d). This hunting caused an ecological imbalance characterized by the deaths of the animals which predated on the extinct herbivores, and over-predation of the remaining herbivores by the carnivores (Alroy, 2001). The availability and reliability of food supply resulted in fast population growth. The situation was significantly different in Africa. In the continent recognized as the cradle of mankind, human beings had co-evolved with the animals and had, over the millenia, recognized human beings as a threat against which they had developed anti-predatory behaviour and mechanisms. Africa thus lost very few herbivore species compared to the rest of the continents.

The overkill hypothesis was not the only explanation advanced to explain the historical extinctions. Some scientists have argued that the extinctions resulted from sweeping climatic changes which led to sudden changes in temperatures, leading to the deaths of thousands of animals. According to these scientists, temperature rises led to the death of most of the furry animals which had adapted to cold environments. Warmer temperatures led to deaths through heat exhaustion and loss of habitat. Large mammals were more vulnerable to the temperature shocks due to the formers lower surface area-to-volume ratio.

Grayson (2007) observes that while the explanations advanced by the different theorists to explain the hold a degree of validity, none of the theories can solely give a full account of the extinctions experienced in the Late Pleistocene age. To advance a full and reliable account of the extinction, scientists need to shift their focus from studying groups of species to studying each species individually. Scientists need to view the extinction as the final part of a long process and therefore need to study the history of the individual species during the period before the extinction and in their different geographical homes. Such studies could reveal that although some species died off as a result of over-hunting, others may have become extinct due to temperature changes or many other reasons.