雅思阅读第019套P1-Mammoth

雅思阅读第019套P1-Mammoth kill

READING PASSAGE 1

You should spend about 20minutes on Questions 1-13, which are based on Reading Passage 1below.

Mammoth kill

A mammoth is any species of theextinct genus Mammuthus, proboscideans commonly equipped with long, curvedtusks and, in northern species, a covering of long hair. They lived from thePliocene epoch (from around 5 million years ago) into the Holocene at about4,500 years ago, and were members of the family Elephantidae, which contains,along with mammoths, the two genera of modern elephants and their ancestors.

A Like their modern relatives,mammoths were quite large. The largest known species reached heights in theregion of 4 m at the shoulder and weights of up to 8 tonnes, whileexceptionally large males may have exceeded 12 tonnes. However, most species ofmammoth were only about as large as a modern Asian elephant. Both sexes boretusks. A first, small set appeared at about the age of six months, and thesewere replaced at about 18 months by the permanent set. Growth of the permanentset was at a rate of about 2.5 to 15.2 cm per year. Based on studies of theirclose relatives, the modern elephants, mammoths probably had a gestation periodof 22 months, resulting in a single calf being born. Their social structure wasprobably the same as that of African and Asian elephants, with females livingin herds headed by a matriarch, whilst bulls lived solitary lives or formedloose groups after sexual maturity.

B MEXICO CITY – Although it’s hard toimagine in this age of urban sprawl and automobiles, North America oncebelonged to mammoths, camels, ground sloths as large as cows, bear-size beaversand other formidable beasts. Some 11,000 years ago, however, these large-bodiedmammals and others – about 70 species in all – disappeared. Their demisecoincided roughly with the arrival of humans in the New World and dramaticclimatic change – factors that have inspired several theories about thedie-off. Yet despite decades of scientific investigation, the exact causeremains a mystery. Now new findings offer support to one of these controversialhypotheses: that human hunting drove this megafaunal menagerie to extinction.The overkill model emerged in the 1960s, when it was put forth by Paul S.Martin of the University of Arizona. Since then, critics have charged that noevidence exists to support the idea that the first Americans hunted to theextent necessary to cause these extinctions. But at the annual meeting of theSociety of Vertebrate Paleontology in Mexico City last October, paleoecologistJohn Alroy of the University of California at Santa Barbara argued that, infact, hunting-driven extinction is not only plausible, it was unavoidable. Hehas determined, using a computer simulation, that even a very modest amount ofhunting would have wiped these animals out.

C Assuming an initial humanpopulation of 100 people that grew no more than 2 percent annually, Alroydetermined that if each band of, say, 50 people killed 15 to 20 large mammals ayear, humans could have eliminated the animal populations within 1,000 years.Large mammals in particular would have been vulnerable to the pressure becausethey have longer gestation periods than smaller mammals and their young requireextended care.

D Not everyone agrees with Alroy’sassessment. For one, the results depend in part on population-size estimatesfor the extinct animals – figures that are not necessarily reliable. But a morespecific criticism comes from mammalogist Ross D. E. MacPhee of the AmericanMuseum of Natural History in New York City, who points out that the relevantarchaeological record contains barely a dozen examples of stone points embeddedin mammoth bones (and none, it should be noted, are known from other megafaunalremains) – hardly what one might expect if hunting drove these animals toextinction. Furthermore, some of these species had huge ranges – the giantJefferson’s ground sloth, for example, lived as far north as the Yukon and asfar south as Mexico – which would have made slaughtering them in numberssufficient to cause their extinction rather implausible, he says.

E MacPhee agrees that humans mostlikely brought about these extinctions (as well as others around the world thatcoincided with human arrival), but not directly. Rather he suggests that peoplemay have introduced hyperlethal disease, perhaps through their dogs orhitchhiking vermin, which then spread wildly among the immunologically naivespecies of the New World. As in the overkill model, populations of largemammals would have a harder time recovering. Repeated outbreaks of ahyperdisease could thus quickly drive them to the point of no return. So farMacPhee does not have empirical evidence for the hyperdisease hypothesis, andit won’t be easy to come by: hyperlethal disease would kill far too quickly toleave its signature on the bones themselves. But he hopes that analyses oftissue and DNA from the last mammoths to perish will eventually revealmurderous microbes.

F The third explanation for whatbrought on this North American extinction does not involve human beings.Instead its proponents blame the loss on the weather. The Pleistocene epochwitnessed considerable climatic instability, explains paleontologist Russell W.Graham of the Denver Museum of Nature and Science. As a result, certainhabitats disappeared, and species that had once formed communities split apart.For some animals, this change brought opportunity. For much of the megafauna,however, the increasingly homogeneous environment left them with shrinking geographicalranges – a death sentence for large animals, which need large ranges. Althoughthese creatures managed to maintain viable populations through most of thePleistocene, the final major fluctuation – the so-called Younger Dryas event –pushed them over the edge, Graham says. For his part, Alroy is convinced thathuman hunters demolished the titans of the Ice Age. The overkill model explainseverything the disease and climate scenarios explain, he asserts, and makesaccurate predictions about which species would eventually go extinct.“Personally, I’m a vegetarian,” he remarks, “and I find all of this kind ofgross – but believable.”

SECTION 1: QUESTIONS 1-13

Questions 1-7

Complete the following summaryof the paragraphs of Reading Passage, using NO MORE THAN THREE WORDS from the Reading Passage for each answer.

Write your answers inboxes 1-7 on your answer sheet.

The reason why had big sizemammals become extinct 11,000 years ago is under hot debate. First explanationis that 1 ________________ ofhuman made it happen. This so called 2 ________________ began from 1960s suggested by anexpert, who however received criticism of lack of further information. Anotherassumption promoted by MacPhee is that deadly 3 ________________ from human causes their demises.However his hypothesis required more 4 ________________ to testify its validity. Grahamproposed a third hypothesis that 5 ________________ in Pleistocene epoch drove somespecies disappear, reduced 6 ________________ poseda dangerous signal to these giants, and 7 ________________ finally wiped them out.

Questions 8-13

Use the information in thepassage to match the people (listed A-C) with opinions or deedsbelow.

Write the appropriateletters A-C in boxes 8-13 on your answersheet.

NB you may use any letter morethan once.

John Alroy

Ross D.E. MacPhee

Russell W. Graham

8 __________ Human hunting well explained whichspecies would finally disappear.

9 __________ Further grounded proof needed toexplain human’s indirect impact on mammals

10 __________ Over hunting situation has causeddie-out of large mammals.

11 __________ Illness rather than hunting causedextensive extinction.

12 __________ Doubt raised through the study ofseveral fossil records.