Part Ⅱ Reading Comprehension （Skimming and Scanning)Directions: In this part, you will hav

Part Ⅱ Reading Comprehension (Skimming and Scanning)

Directions: In this part, you will have 15 minutes to go over the passage quickly and answer the questions on Answer Sheet 1.

For questions 1-4, mark

Y (for YES) if the statement agrees with the information given in the passage;

N (for NO) if the statement contradicts the information given in the passage;

NG (for NOT GIVRN) if the information is not given in the passage.

For questions 5-10, complete the sentences with the information given in the passage.

Unity and Diversity

Many physicists are engaged in the search for a "theory of everything". Biologists, smugly, think they have found one already. Organisms that survive long enough to reproduce and are attractive enough to find a mate pass their genes on to the next generation. Those that do not are evolutionary cul-de-sacs. But the details—how you go on from the basic principles of evolution to explain large-scale patterns in biology—are more divisive. Scientific camps form. Their leaders step onto soap boxes. And only rarely do people concede that their own theories and those of their opponents are not always mutually exclusive.

Since the early 1970s, the two grandest patterns of life—how species are arranged in space and how they are arranged in time—have divided their opposing camps quite neatly. Those who squabble over space disagree about why there are more species in the tropics than anywhere else. To them, the tropics are either where species are more often born (cradles of diversity) or where they tend not to die (museums of diversity). By contrast, biologists concerned with patterns in time tenaciously debate whether new species come into being in a smooth and gradual manner, or whether the history of life is actually a series of bursts of change that are interspersed with periods when nothing much happens.

Two papers just published in Science have cast light on these questions, and their findings, if not necessarily resulting in compromise, do show the value of taking leaves out of other people's books. The "space biologists" have looked into time, namely the fossil record over the past 11m years. Meanwhile the "time biologists" have looked at the here and now and found evidence in living species for periods of rapid evolution in their genes.

Biological Spacetime

The space biologists have the advantage that they agree about the pattern they are trying to explain. Almost all groups of life that have been studied—be they fungi, plants, vertebrates or invertebrates, and no matter whether they occur in forests, streams or seas—seem to have more species the closer they are to the equator.

To decide whether the tropics are a cradle or a museum, though, involves picking this pattern apart with statistics. And statistics work best when you have more than one sample. That is the reason for reaching into the past.

David Jablonski, of the University of Chicago, and his colleagues created their samples by dividing the past 11m years into three periods. For simplicity's sake, they also chopped the Earth's surface into two: tropical regions and everywhere else, which they called the "extratropics".

To avoid sampling bias, they restricted their analysis to one group of animals—the bivalve molluscs—that fossilise well. This allowed them to follow 431 "lineages" of marine bivalve through the course of geological time. The vast majority of these lineages appear in the tropics and then spread into the extratropics, in other words, the tropics do, indeed, act as cradles of biodiversity.

In fact, the pattern Dr Jablonski reports is probably more marked than

A．Y

B．N

C．NG