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(It was) the (split of) eleven southern (states) from the Union in 1861 that (leading) to the Civil War in the United States.
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Many prehistoric people subsisted as hunters and gatherers. Undoubtedly, game animals, including some very large species, provided major components of human diets. An important controversy centering on the question of human effects on prehistoric wildlife concerns the sudden disappearance of so many species of large animals at or near the end(5) of the Pleistocene epoch. Most paleontologists suspect that abrupt changes in climate led to the mass extinctions. Others, however, have concluded that prehistoric people drove many of those species to extinction through over-hunting. In their "Pleistocene overkill hypothesis," they cite what seems to be a remarkable coincidence between the arrival of prehistoric peoples in North and South America and the time during which mammoths,(10) giant ground sloths, the giant bison, and numerous other large mammals became extinct. Perhaps the human species was driving others to extinction long before the dawn of history. Hunter-gatherers may have contributed to Pleistocene extinctions in more indirect ways. Besides over-hunting, at least three other kinds of effects have been suggested: direct competition, imbalances between competing species of game animals, and early(15) agricultural practices. Direct competition may have brought about the demise of large carnivores such as the saber-toothed cats. These animals simply may have been unable to compete with the increasingly sophisticated hunting skills of Pleistocene people. Human hunters could have caused imbalances among game animals, leading to the extinctions of species less able to compete. When other predators such as the gray wolf(20) prey upon large mammals, they generally take high proportions of each year s crop of young. Some human hunters, in contrast, tend to take the various age-groups of large animals in proportion to their actual occurrence. If such hunters first competed with the larger predators and then replaced them. they may have allowed more young to survive each year, gradually increasing the populations of favored species As these populations expanded,(25) they in turn may have competed with other game species for the same environmental niche, forcing the less hunted species into extinction. This theory, suggests that human hunters played an indirect role in Pleistocene extinctions by hunting one species more than another. What does the passage mainly discuss
Many ants forage across the countryside in large numbers and undertake mass migrations; these activities proceed because one ant lays a trail on the ground for the others to follow. As a worker ant returns home after finding a source of food, it marks the route by intermittently touching its stinger to the ground and depositing a tiny amount of trail(5)pheromone—a mixture of chemicals that delivers diverse messages as the context changes. These trails incorporate no directional information and may be followed by other ants in either direction. Unlike some other messages, such as the one arising from a dead ant, a food trail has to be kept secret from members of other species. It is not surprising then that ant species use(10)a wide variety of compounds as trail pheromones. Ants can be extremely sensitive to these signals. Investigators working with the trail pheromone of the leafcutter ant Atta texana calculated that one milligram of this substance would suffice to lead a column of ants three times around Earth. The vapor of the evaporating pheromone over the trail guides an ant along the way, (15)and the ant detects this signal with receptors in its antennae. A trail pheromone will evaporate to furnish the highest concentration of vapor right over the trail, in what is called a vapor space. In following the trail, the ant moves to the right and left, oscillating from side to side across the line of the trail itself, bringing first one and then the other antenna into the vapor space. As the ant moves to the right, its left antenna arrives in the vapor space. (20)The signal it receives causes it to swing to the left, and the ant then pursues this new course until its right antenna reaches the vapor space. It then swings back to the right, and so weaves back and forth down the trail. According to the passage, why do ants use different compounds as trail pheromones
Native Americans probably arrived from Asia in successive waves over several millennia, crossing a plain hundreds of miles wide that now lies inundated by 160 feet of water released by melting glaciers. For several periods of time, the first beginning around 60,000 B.C. and the last ending around 7,000 B.C., this land bridge was open. The (5) first people traveled in the dusty trails of the animals they hunted. They brought with them not only their families, weapons, and tools but also a broad metaphysical understanding, sprung from dreams and visions and articulated in myth and song, which complemented their scientific and historical knowledge of the lives of animals and of people. All this they shaped in a variety of languages, bringing into being oral literatures of power and beauty. (10) Contemporary readers, forgetting the origins of western epic, lyric, and dramatic forms, are easily disposed to think of “literature” only as something written. But on reflection it becomes clear that the more critically useful as well as the more frequently employed sense of the term concerns the artfulness of the verbal creation, not its mode of presentation. Ultimately, literature is aesthetically valued, regardless of language, culture,(15)or mode of presentation, because some significant verbal achievement results from the struggle in words between tradition and talent. Verbal art has the ability to shape out a compelling inner vision in some skillfully crafted public verbal form. Of course, the differences between the written and oral modes of expression are not without consequences for an understanding of Native American literature. The essential(20)difference is that a speech event is an evolving communication, an “emergent form,” the shape, functions, and aesthetic values of which become more clearly realized over the course of the performance. In performing verbal art , the performer assumes responsibility for the manner as well as the content of the performance, while the audience assumes the responsibility for evaluating the performer’s competence in both areas. It is this intense(25)mutual engagement that elicits the display of skill and shapes the emerging performance. Where written literature provides us with a tradition of texts, oral literature offers a tradition of performances. According to the passage, why did the first people who came to North America leave their homeland
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