托福TPO42阅读Passage1原文文本+题目+答案解析|江阴雨辰互联

2024年4月21日发(作者：打印机的安装方法)

　　为了帮助大家高效备考托福，为大家带来托福TPO42阅读Passage1原文文本+题目+答案

解析，希望对大家备考有所帮助。

　　Geographic Isolation of Species

　　Biologist Ernst Mayr defined a species as“an actually or potentially

interbreeding population that does not interbreed with other such populations when

there is opportunity to do so.”A key event in the origin of many species is the

separation of a population with its gene pool(all of the genes in a population at

any one time)from other populations of the same species,thereby preventing population

interbreeding With its gene pool isolated,a separate population can follow its own

evolutionary the formation of many species,the initial isolation of a

population seems to have been a geographic barrier This mode of evolving new species

is called allopatric speciation.

　　Many factors can isolate a population geographically.A mountain range may emerge

and gradually split a population of organisms that can inhabit only lowland

lakes,certain fish populations might become isolated in this rity,a

creeping glacier may gradually divide a population,or a land bridge such as the

Isthmus of Panama may form and separate the marine life in the ocean waters on either

side.

　　How formidable must a geographic barrier be to keep populations apart?It depends

on the ability of the organisms to move across and coyotes can easily

cross mountains and passage of wind-blown tree pollen is also not hindered

by such barriers,and the seeds of many plants may be earned back and forth on animals

In contrast,small rodents may find a deep canyon or a wide river an effective

example,the Grand Canyon,in the southwestern United Slates,separate the

range of the while-tailed antelope squirrel from that of the closely related

Harris’antelope r,with a shorter tail that is white

underneath,the white-tailed antelope squirrel inhabits deserts north of the canyon

and west of the Colorado River in southern California Hams'antelope squirrel has a

more limited range in deserts south of the Grand Canyon.

　　Geographic isolation creates opportunities for new species to develop,but it does

not necessarily lead to new species because speciation occurs only when the gene pool

undergoes enough changes to establish reproductive barriers between the isolated

population and its parent likelihood of allopatric speciation

increases when a population is small as well as isolated,making it more likely than

a large population to have its gene pool changed example,in less

than two million years,small populations of stray animals and plants from the South

American mainland that managed to colonize the Galapagos Islands gave rise to all

the species that now inhabit the islands.

　　When oceanic islands are far enough apart to permit populations to evolve in

isolation,but close enough to allow occasional dispersions to occur,they are

effectively outdoor laboratories of Galapagos island chain is one of

the world s greatest showcases of evolution Each island was born from underwater

volcanoes and was gradually covered by organisms derived from strays that rode the

ocean currents and winds from other islands and sms can also be

carried to islands by other organisms,such as sea birds that travel long distances

with seeds clinging to their feathers.

　　The species on the Galapagos Islands today,most of which occur nowhere

else,descended from organisms that floated,flew,or were blown over the sea from the

South American mainland For instance,the Galapagos island chain has a total of

thirteen species of closely related birds called Galapagos finches These birds have

many similarities but differ in their feeding habits and their beak type,which is

correlated with what they eat Accumulated evidence indicates that all thirteen finch

species evolved from a single small population of ancestral birds that colonized one

of the tely isolated on the island after migrating from the

mainland,the founder population may have undergone significant changes in its gene

pool and become a new ,a few individuals of this new species may have

been blown by storms to a neighboring ed on this second island,the second

founder population could have evolved into a second new species,which could later

recolonize the island from which its founding population each

Galapagos island has multiple species of finches,with as many as ten on some islands.

　　paragraph 1