A mammoth is any species of the extinctgenus Mammuthus, proboscideans commonly equipped with long, curved tusks and,in northern species, a covering of long hair. They lived from the Plioceneepoch (from around 5 million years ago) into the Holocene at about 4,500 yearsago, and were members of the family Elephantidae, which contains, along withmammoths, the two genera of modern elephants and their ancestors.
A
Like their modern relatives, mammothswere quite large. The largest known species reached heights in the region of 4m at the shoulder and weights of up to 8 tonnes, while exceptionally largemales may have exceeded 12 tonnes. However, most species of mammoth were onlyabout as large as a modern Asian elephant. Both sexes bore tusks. A first,small set appeared at about the age of six months, and these were replaced atabout 18 months by the permanent set. Growth of the permanent set was at a rateof about 2.5 to 15.2 cm per year. Based on studies of their close relatives,the modern elephants, mammoths probably had a gestation period of 22 months,resulting in a single calf being born. Their social structure was probably thesame as that of African and Asian elephants, with females living in herdsheaded by a matriarch, whilst bulls lived solitary lives or formed loose groupsafter 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 human population of100 people that grew no more than 2 percent annually, Alroy determined that ifeach band of, say, 50 people killed 15 to 20 large mammals a year, humans couldhave eliminated the animal populations within 1,000 years. Large mammals inparticular would have been vulnerable to the pressure because they have longergestation periods than smaller mammals and their young require extended 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 to extinction.Furthermore, some of these species had huge ranges – the giant Jefferson’sground sloth, for example, lived as far north as the Yukon and as far south asMexico – which would have made slaughtering them in numbers sufficient to causetheir extinction rather implausible, he says.
E
MacPhee agrees that humans most likelybrought 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 h
The third explanation for what brought onthis North American extinction does not involve human beings. Instead itsproponents blame the loss on the weather. The Pleistocene epoch witnessedconsiderable climatic instability, explains paleontologist Russell W. Graham ofthe Denver Museum of Nature and Science. As a result, certain habitatsdisappeared, and species that had once formed communities split apart. For someanimals, 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 of gross – butbelievable.”
Questions 1-7
Complete the following summary of theparagraphs of Reading Passage, using NO MORE THAN THREEWORDS from the Reading Passage for each answer.
Write your answers inboxes 1-7 on your answer sheet.
The reason why had big size mammalsbecome extinct 11,000 years ago is under hot debate. Firstexplanation is that 1…… of human made it happen. This socalled 2…… began from 1960s suggested by an expert, who howeverreceived criticism of lack of further information. Another assumption promotedby MacPhee is that deadly 3…… from human causes their demises.However his hypothesis required more 4…… to testify itsvalidity. Graham proposed a third hypothesis that 5…… inPleistocene epoch drove some species disappear,reduced 6…… posed a dangerous signal to these giants,and 7…… finally wiped them out.
Questions 8-13
Use the information in the passage tomatch the people (listed A-C) with opinions or deeds below.
Write the appropriateletters A-C in boxes 8-13 on your answer sheet.
NB you may use anyletter more than once.
A John Alroy
B Ross D.E. MacPhee
C 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 caused extensiveextinction.
12. Doubt raised through the study ofseveral fossil records.
13. Climate shift is the main reason ofextinction.
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