The human species came into being at the time of the greatest biological diversity in the history of the Earth. Today, as human populations expand and alter the natural environment, they are reducing biological diversity to its lowest level since the end of the Mesozoic era, 65 million years ago. The ultimate consequences of this biological collision are beyond calculation, but they are certain to be harmful, That, in essence, is the biodiversity crisis.

The history of global diversity can be summarized as follows： after the initial flowering of multi cellular animals, there was a swift rise in the number of species in early Paleozoic times （between 600 and 430 million years ago）, then plateaulike stagnation for the remaining 200 million years of the Paleozoic era, and finally a slow but steady climb through the Mesozoic and Cenozoic eras to diversity's all-time high. This history suggests that biological diversity was hard won and a long time in coming.

Furthermore, this pattern of increase was set back by five massive extinction episodes, The most recent of these, during the Cretaceous period, is by far the most famous, because it ended the age of the dinosaurs, conferred hegemony on the mammals, and ultimately made possible the ascendancy of the human species, But the cretaceous crisis was minor compared with the Permian extinctions 240 million years ago, during which between 77 and 96 percent of marine animal species perished. It took 5 million years. well into Mesozoic times. for species diversity to begin a significant recovery.

Within the past 10,000 years biological diversity has entered a wholly new era. Human activity has had a devastating effect on species diversity, and the rate of human-induced extinctions is accelerating. Half of the bird species of Polynesia have been eliminated through hunting and the destruction of native forests. Hundreds of fish species endemic to Lake Victoria are now threatened with extinction following the careless introduction of one species of fish. the Nile perch. The list of such bio geographic disasters is extensive.

Because every species is unique and irreplaceable, the loss of biodiversity is the most profound process of environmental change. Its consequences are also the least predictable because the value of Earth's biota （the fauna and flora collectively） remains largely unstudied and unappreciated； unlike material and cultural wealth, which we understand because they ar the substance of our everyday lives. Biological wealth is usually taken for granted. This is a serious strategic error, one that will be increasingly regretted as time passes. The biota is not only part of a country's heritage. the product of millions of years of evolution centered on that place； it is also a potential source for immense untapped material wealth in the form of food, medicine, and other commercially important substance.

7. Which one of the following best expresses the main idea of the passage？

（A） The reduction in biodiversity is an irreversible process that represents a setback both for science and for society as a whole.

（B） The material and cultural wealth of a nation are insignificant when compared with the country's biological wealth.

（C） The enormous diversity of life on Earth could not have come about without periodic extinctions that have conferred preeminence on one species at the expense of another.

（D） The human species is in the process of initiating a massive extinction episodes look minor by comparison.

（E） The current decline in species diversity is human-induced tragedy of incalculable proportions that has potentially grave consequences for the human species.

8. Which one of the following situations is most analogous to the history of global diversity summarized in lines 10-18 of the passage？

（A） The number of fish in a lake declines abruptly as a result of water pollution. Then makes a slow comeback after cleanup efforts and the passage of ordinances against dumping.

（B） The concentration of chlorine in the water supply of large city fluctuates widely before stabilizing at a constant and safe level.

（C） An old-fashioned article of clothing goes in and out of style periodically as a result of features in fashion magazines and the popularity of certain period films.

（D） After valuable mineral deposits are discovered, the population of a geographic region booms then levels off an d begins to decrease at a slow and steady race.

（E） The variety of styles stocked by a shoe store increases rapidly after the store opens, holds constant for many months, and then gradually creeps upward.

9. The author suggests which one of the following about the Cretaceous crisis？

（A） It was the second most devastating extinction episode in history.

（B） It was the most devastating extinction episode up un until that time.

（C） It was less devastating to species diversity than is the current biodiversity crisis.

（D） The rate of extinction among marine animal species as a result of the crisis did not approach 77 percent.

（E） The dinosaurs comprised the great majority of species that perished during the crisis.

10. The author mentions the Nile perch in order to provide an example of

（A） a species that has become extinct through human activity

（B） the typical lack of foresight that has led to biogeographic disaster

（C） a marine animal species that survived the Permian extinctions

（D） a species that is a potential source of material wealth

（E） the kind of action that is necessary to reverse the decline in species diversity

11. All of the following are explicitly mentioned in the passage as contributing to the extinction of species EXCEPT

（A） hunting

（B） pollution

（C） deforestation

（D） the growth of human populations

（E） human-engineered changes in the environment

12. The passage suggests which one of the following about material and cultural wealth？

（A） Because we can readily assess the value of material and cultural wealth, we tend not to take them for granted.

（B） Just as the biota is a source of potential material wealth, it is an untapped source of cultural wealth as well.

（C） some degree of material and cultural wealth may have to be sacrificed if we are to protect our biological heritage.

（D） Material and cultural wealth are of less value than biological wealth because they have evolve over a shorter period of time.

（E） Material wealth and biological wealth are interdependent in a way that material wealth and cultural wealth are not.

13. The author would be most likely to agree with which one of the following statements about the consequences of the biodiversity crisis？

（A） The loss of species diversity will have as immediate an impact on the material of nations as on their biological wealth.

（B） The crisis will likely end the hegemony of the human race and bring about the ascendancy of another species.

（C） The effects of the loss of species diversity will be dire, but we cannot yet tell how dire.

（D） it is more fruitful to discuss the consequences of the crisis in terms of the potential loss to humanity than in strictly biological loss to humanity than in strictly biological terms.

（E） The consequences of the crisis can be minimized, but the pace of extinctions can not be reversed.