Passage 2 Ever since Darwin’s theory of evolution, biologists have assumed that environments teeming with complex forms of life served as the nurseries of evolution. But two recent papers in Science magazine have turned that notion on its head. Last month some biologists reported that in the ocean it is the relatively barren areas that serve as “evolutionary crucibles(熔爐),” not regions with great diversity of species. Other researchers announced this summer that the Arctic, not the rain forest, spawned many plants and animals that later migrated to North America. Says John Sepkoski of the University of Chicago, “Harsh environments may be producing the major changes in the history of life.”
These “changes” do not result merely in a longer tail or a bigger claw for an existing species but, rather, in dramatic leaps up the evolutionary ladder — a rare innovation that comes along once in a million years. In the Arctic, reports Leo Hickey of Yale University, the innovations ran to forms never before seen on earth. By dating fossils from many geologic layers, he concluded that large grazing animals first appeared in the Arctic and migrated to temperate places a couple of million years or so later. Among plants, species of redwood and birch originated in polar regions some 18 millions years before they showed up in the south. Examining fossils as old as 570 million years, Chicago’s Sepkoski found that shell-less, soft-bodied creatures were suddenly replaced by trilobites（三葉蟲）, then by the more advanced clam-like animals. These changes, he notes, “first become common near shore.” That surprised him — an environment with as few species as exist in the near shore, and with such a poor record of producing new species, seems an unlikely place for biological innovation. But when Jablonski dated fossils of 100 million years ago, he found that during this era, too, the near shore spawned biological breakthroughs — more sophisticated sea creatures that move and find food in ocean sediments instead of passively filtering whatever floats by.
The findings are too new to apply to human evolution, but at first glance they seem to fit the facts. Anthropologists believe that our ancestors became fully human only after they left their secure life in the trees for the harsh world of savanna(plain without trees). There, the demanding conditions triggered that most human of traits, the large brain, and the most profound evolutionary step of all was taken.
26. Two recent papers in Science magazine claim to have found evidence which contradicts the traditional notion that _______.
A) relatively harsh environments are the nurseries of evolution
B) evolution occurred in regions with biological diversity
C) new forms of life come into being in near-shore areas
D) species of birch and redwood originated in the south
27. According to Leo Hickey of Yale University, which of the following may have spawned more advanced species of land animals?
A) The barren ocean floor
B) The Arctic
C) The rain forest
D) Temperate Zones
28. The word “innovations” in the second paragraph means ________.
A) New theory B) New phenomenon C) Changes D) New inventions
29. How would anthropologists take the new findings?
A) They would look at them dubiously
B) They would eagerly apply them to the study of human evolution
C) They would challenge them, though at first glance they tend to look at them favorably
D) They would most probably think the new findings fit well into their theory
30. Which of the following may be an appropriate title of the passage ?
A) Darwin’s Theory Modified
B) How Animals Evolve
C) Evolution in Hard Places
D) Where Did Large Sea Animals Originate
Passage 3
A classic series of experiments to determine the effects of overpopulation on communities of rats was conducted by a psychologist, John Calhoun. In each experiment, an equal number of male and female adult rats were placed in an enclosure. The rat populations were allowed to increase. Calhoun knew from experience approximately how many rats could live in the enclosures without experiencing stress due to overcrowding. He allowed the population to increase to approximately twice this number. Then he stabilized the population by removing offspring that were not dependent on their mothers. At the end of the experiments, Calhoun was able to conclude that overcrowding causes a breakdown in the normal social relationships among rats, a kind of social disease. The rats in the experiments did not follow the same patterns of behavior as rats would in a community without overcrowding.
The females in the rat population were the most seriously affected by the high population density. For example, mothers sometimes abandoned their pups, and, without their mothers’ care, the pups died. The experiments verified that in overpopulated communities, mother rats do not behave normally. Their behavior may be considered diseased, pathological (病理學的).
The dominant males in the rat population were the least affected by over population. Each of these strong males claimed an area of the enclosure as his own. Therefore, these individuals did not experience the overcrowding in the same way as the other rats did. However, dominant males did behave pathologically at times. Their antisocial behavior consisted of attacks on weaker male, female, and immature rats. This deviant behavior showed that even though the dominant males had enough living space, they too were affected by the general overcrowding.
Non-dominant males in the experimental rat communities also exhibited deviant social behavior. Some withdrew completely, avoiding contact with other rats. Other non-dominant males were hyperactive, chasing other rats and fighting each other.
The behavior of the rat population has parallels in human behavior. People in densely populated areas exhibit deviant behavior similar to that of the rats in Calhoun's experiments. In large urban areas, such as New York City, London, and Cairo, there are abandoned children. There are cruel, powerful individuals, both men and women. There are also people who withdraw and people who become hyperactive. Is the principal cause of these disorders overpopulation? Calhoun's experiments suggest that it might be. In any ease, social scientists and city planners have been influenced by the results of this series of experiments.
31. Calhoun stabilized the rat population ____.
A) when it was double the number that could live in the enclosure without stress
B) by removing young rats
C) so that there was a constant number of adult rats in the enclosure
D) All of the above are correct
32. Which of the following inferences can NOT be made from the first paragraph?
A) Calhoun’s experiment is still considered important today.
B) Overpopulation causes pathological behavior in rat populations.
C) Stress does not occur in rat communities unless there is overcrowding.
D) Calhoun had experimented with rats before.
33. According to the passage, which of the following is NOT true?
A) Dominant males had adequate living space.
B) Dominant males were not as seriously affected by overcrowding as the other rats.
C) Dominant males attacked weaker rats.
D) The strongest males are always able to adapt to bad conditions.
34. The author implies that the behavior of the dominant male rats is sometimes parallel with
that of _____.
A) cruel, powerful people
B) people who abandon their children
C) hyperactive people
D) people who would like to keep to themselves.
35. The main point of this passage is that _______.
A) although rats are affected by overcrowding, people are not
B) overcrowding may be an important cause of social pathology
C) the social behavior of rats is seriously affected by overcrowding
D) Calhoun's experiments have influenced many people
2006年12月英語四六級考試最后沖刺專題
希望與其他英語愛好者進行交流？點擊進入外語論壇>>>
更多信息請訪問：考試吧四六級欄目
