問題詳情
C.Prehistoric peoples subsisted for the most part as hunters and gatherers; they weredependent on what the ecosystem could provide naturally and probably did little or nothing,apart from devising more effective methods of hunting, to modify that output. However, thisshould not be taken as meaning they had no impact on their environment. Undoubtedly theanimals they shared the plains and forests with, including some very large and impressivespecies, comprised an important part of the human diet. Assuming our ancestors were morethan just scavengers; that they actively sought and killed their prey, they would have had atleast as great an effect on the populations of those animals as did any other predator. Inactuality, the impact was probable much greater given the relatively advanced capacity ofhumans to learn from mistakes; to modify their behavior based on observed results, and topass on the accumulating lessons from generation to generation.Among paleontologists there is an important controversy centering on the question ofjust how profound the effect of human activity was on prehistoric wildlife; in particular, howmuch human hunters contributed to the sudden disappearance of so many species of largeanimals from the North American continent between 10,000 and 12,000 years ago, at or nearthe end of the Pleistocene Epoch. One school of thought attributes the extinctions to climaticchange too abrupt to allow adaptation by larger species. Another group, however, points to adifferent possibility. They support the view that the prehistoric Homo sapiens drove many ofthose species to extinction, mainly through over hunting. This has come to be known as the“Pleistocene Overkill Hypothesis.”This theory helps explain what, in its absence, could only be regarded as a remarkablecoincidence between the arrival of prehistoric peoples in the Western Hemisphere and thedisappearance of mammoths, giant ground sloths, the giant bison, and numerous other largeland mammals. Maybe, as the theory’s proponent’s claim, human-caused extinction is notexclusively a modern phenomenon; perhaps the human species has been driving otherspecies to extinction since long before the dawn of history, and in complex ways that gobeyond the immediate result of killing individual animals for food.The reduction of animal populations through direct predation might be the mostobvious mechanism of influence, but it may not have been the only one. Humanhunter-gatherers could have contributed to the Pleistocene extinctions in more indirect ways.At least three other mechanisms have been suggested: direct competition, human-includedimbalances between competing species of game animals, and early agricultural practices.Direct competition might have brought about the demise of large carnivores; animalssuch as the saber-toothed cats. Though probably too formidable to have been the objects ofhuman hunting activity themselves, these animals would have preyed on many of the samespecies humans hunted. Their strength and speed would have proved inadequate when facedwith human competition. Consequently, they would have suffered as the numbers ofpotential prey shrank.Human activity could have created competitive imbalances among prey species as well.It is a generally recognized characteristic of predation that when non-human hunters, eventhose that hunt cooperatively, like wolves for example, prey on animals larger thanthemselves, they generally take higher proportions of each year’s population of young.This is simply opportunism combined with risk reduction. The young are the most vulnerableand the least likely to cause injury to the predator during the kill. In contrast, human hunters,benefiting from their intelligence, ingenuity and adaptability, suffer fewer limitations andrisks. As a result, when hunting larger animals, they tend to take the various age-groups incloser proportion to their actual occurrence.If human hunters first competed with the larger predators and then eventually replacedthem, they may have allowed more of the young of certain prey species to survive with eachsuccessive year, thus allowing the populations of these favored species to increase. As thesepopulations expanded, they would have competed with other game species for the sameinventory of environmental resources. Ultimately and somewhat ironically, this could haveled to the extinction of the species less often hunted by humans.
【題組】27.What does the passage mainly discuss?
(A) The effects of human activities on prehistoric wildlife.
(B) The origins of the hunter-gatherer way of life.
(C) The evolution of predators during the Pleistocene Epoch.
(D) Why humans were the most effective Pleistocene predators.
參考答案
答案：A
難度：適中0.666667
統計：A(16),B(3),C(1),D(2),E(0)