【正文】 ent Um...sure. But...about mypaper ...What question should I be asking mygrandmother? Professor You know what, I have a meeting now. Why don’tyou e to class a fewminutes early tomorrow? Student Will do. LectureZoology (The Sixth Mass Extinction) Narrator Listen to part ofa lecturein a zoology class. Professor A mass extinction is when numerousspecies bee extinctover a veryshort time period, short, geologically speaking that is, like when the dinosaurs died out 65 million years ago. And the fossil record,it indicates that in all the time thatanimals have inhabited Earth, there have been five great mass extinctions, dinosaurs being themost each of theothers up to half of all 全國免費咨詢電話： 4000123267 land animals and up to 95 percentof marine species disappeared. Well, todaywe are witnessing a sixth mass extinction, but unlike the others,the currentloss of biodiversity can be traced tohuman activity. Since the Stone Age, humans have been eliminating species and altering ecosystems with astounding speed. Countless species have disappeared due to overhunting, habitat destruction and habitat fragmentation, polution and other unnatural human causes. So, as a way ofrepairing some ofthat damage, a group of conservation biologists has proposed an amibitious – or some might say – a radical plan, involving large vertebrates, or,megafauna. Megafauna include elephants, wild horses, big cats, camels, large animals. Eh, actually,the proposal focuses on a particular subset ofmegafauna, the kind that lived during thePleistocene epoch. OK. The Pleistocene epoch, most monly known as the Ice Age,stretched from million to 11,500 years ago. In the Americas,many megafauna began disappearing bythe end of the Pleistocene. So here’s the biologists’ idea. Takea selectgroup of animals, megafauna from places like Africa and Asia, and introduce them into other systemssimilar to theircurrent homes, beginning in the westernUnited States. Theycalltheir plan Pleistocene rewilding . 全國免費咨詢電話： 4000123267 Now,the advocatesof Pleistocene rewilding cite two main goals. One is to help prevent the extinction ofsome endangered megafauna by providing new refuges,new habitats for them. The other is torestore some of theevolutionary and ecological potentialthat has been lost in North America. What do I mean by restoreevolutionary potential? Well,as you know, theevolution of any species is largely influenced by itsinteractionswith otherspecies. So during thePleistocene epoch ...Let ’s takethe now extinct American cheetah, for instance. We believe it played a pivotal role in the evolution of the pronghorn antelope,the antelope’s amazing speed, tobe exact,because natural selection would favor those antelope that could outrun a cheetah. When the American cheetahs disappeared, their influence on theevolution of pronghorn and presumably6 on other preyanimals stopped. So it is conceivable7 that the pronghorn antelope would have continued to evolve,get faster maybe, if thecheetahs werestill around. That ’s what ’s meant by evolutionary potential . Importing African cheetahsto the westernUnited Statescould, in theory,put the pronghorn back onto its...uh, natural evolutionary trajectoryaccording to these biologists. Another example is the interaction of megafauna with local flora, in particular,plants that relyon animals to disperse their seeds .Like Pleistocene rewilding could spark thereemergence of large 全國免費咨詢電話： 4000123267 seeded American plants, such as the maclura tree .Many typesof maclura used to grow in North America,but today,just one varietyremains and it is found in only two the distant past, large herbivores like mastodons8 dispersed maclura seeds, each the size of an orange in their droppings. Well, therearen’tany mastodons left, but thereare elephants, which descended from mastodons. Introduceelephants into that ecosystem and theymight disperse those large maclura seeds, like their ancestorsdid. Getthe idea? Restoring some of theformer balance to theecosystem? Butas I alluded to earlier, Pleistocene rewilding is extremelycontroversial. A big worry is that these transplanted megafauna might devastateplants and animals that arenative to thewestern United the yearssince thePleistocene epoch, native species have adapted to thechanging environmentalthere,plants, smaller animals, theyhave been evolving without megafauna for millennia. Also, animal species that went extinct 11,000 years ago, uh, some are quite different geicallyfrom their modernday counterparts, like elephants don’t have thick coatslike their mastodon ancestorsdo when theygrazethe prairies ofthe America West duri