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Martin (1968, 1984, 1990) has summarized the evidence for the world-wide
extinction of late Pleistocene megafauna.
In Africa and Asia 15–20 percent of the genera disappeared 80–60,000 years B.P.; in Australia 94 percent were lost from 40–15,000 years B.P.; North and South America
experienced a 70–80 percent loss in the last 15,000 years, with an abrupt(突然的) North American loss of mammoth, mastodon, ground sloth, and such dependent predators and scavengers as the saber toothed cat and (in much of its range) the condor 11,000 years ago. The horse and two subspecies of bison were gone by 9–8,000 years ago. This worldwide pattern correlates suspiciously with the chronology of human colonization leading to Paul Martin's hypothesis that extinction was directly or indirectly due to “overkill” by exceptionally competent hunter cultures. This model explains the light extinctions in Africa and Asia where modern humankind “grew up,” allowing gradual adaptation to humankind's accumulating proficiency as a superpredator; it explains the abrupt massive losses in Australia and the Americas—the only habitable continents that
were colonized suddenly by advanced stone-aged humans. But the control cases for Martin's “experiment” are the large oceanic islands such as Madagascar and New
Zealand; both were colonized within the last 1000 years, and both suffered a wave of extinctions at this time.
One wonders, if extinction was due to climatic change, why Madagascar extinctions were not coincident with those of Africa 220 miles off its coast, and those of Australia were not coincident with New Zealand extinctions; and why European and Ukrainian mammoths became extinct 13,000 years B.P. while in North America they survived another 2000 years. Previous great extinction waves had affected plants and small animals as well as large animals, but the late Pleistocene extinctions are concentrated on the large gregarious herding, or slow moving, animals—the ideal prey of human hunters. Such large genera are also the animals that are slower growing, have longer gestation periods, require longer periods of maternal care, and live longer. Consequently they were more vulnerable to hunting pressure because reductions in biomass require more time to recover. The theory is bold—some say fanciful.
A counter argument is that there is little direct evidence of hunting; that Paleolithic peoples “probably” relied on plants. But if the fossil record of hunting is “small,” the fossil evidence of gathering is virtually non-existent.
A second counter argument is that there would not have been an incentive to overproduce in excess of immediate needs; that this occurs only in modern exchange
economies. But this argument fails to recognize that in the absence of private property rights, there is no intertemporal incentive to avoid the
kind of waste associated with large kills. What controls the slaughter of domestic cattle is the comparative value of dressed versus live beef. Since no one owned the mammoth, their harvest value (net of hunting cost) contrasted sharply with their zero live procreation value to the individual hunter. A third argument finds it incomprehensible that mere bands of men could have wiped out the great mammoth and two subspecies of bison. It takes a particularly skilled modern rifleman to stop a charging African elephant in time to prevent injury, and extant bison react quickly and violently when they sense danger.
Such observations may simply tell us that these particular subspecies have survived because they were selected for their successful defensive characteristics. We know nothing of the behavioral properties of extinct species which may have been far more approachable than their surviving relatives. While the African and Indian elephants are both members of the same genus, their fossil similarities fail to inform us that the Indian elephant is docile and easily trained for circus display, while the African elephant is not. No one has successfully domesticated the African zebra; in contrast, the Tarpan horse has been domesticated since ancient times (5000–2500 B.P.). Equus includes horses, asses and zebras—all behaviorally distinct animals. |
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