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词汇提示

1.extinctions 灭绝

2.presence 存在

3.eliminated 淘汰

4.disrupt 扰乱

5.emerged 出现

6.prehistoric 史前时期

7.pigeon 鸽子

8.prairie 大草原

9.bison 野牛

10.habitat 栖息地

11.ivory 象牙

12.rhinoceros 犀牛

13.tragic 悲剧地

14.aphrodisiaca 壮阳药

15.stimulants 兴奋剂

原文

Extinctions

Ever since human beings appeared on the earth，we have had a serious impact on other living things.

One of the most serious of the human presence had been the extinction of other species.

Since the arrival of humans，many species of animals and plants have died out as a result of human activity.

The extinction of species is a serious problem.

When certain species are eliminated，this may disrupt the balance of nature，leading to overpopulation of some species and extinction of others.

These changes may have an impact on humans.

Also，some of the species that become extinct might have had benefits for human beings.

For example，some scientists believe that some of the plants growing in rain forest areas might be valuable for treating human diseases.

If these plants become extinct as a result of human activity，then these treatments will never be found.

The earliest extinctions caused by humans occurred very long ago.

Modern human emerged in Africa over 100000 years ago，and some of those people migrated to other parts of the world.

When they reached new areas，they found that it was very easy to hunt the large animals，which had not previously been hunted by humans.

As these prehistoric people moved into the Europe，Australia，and the Americas，they killed large numbers of large animals.

Within a few hundred years，many species of animals had become extinct.

For example，prehistoric people reached New Zealand less than 100 years ago，but they soon hunted a huge bird，called the giant moa，to extinction.

With the beginnings of modern technology，several hundred years ago，many other species were driven to extinction.

Hunters armed with guns were able to kill vast numbers of animals.

In North America，these led to the extinction of bird species such as the passenger pigeon，which has previously been very numerous.

Other species were nearly wiped out，such as the large prairie mammals called bison.

There were once million of these animals，but now only a few thousand remain.

Today，many more species of animals and plants are going extinct.

Sometimes this happens because of human expansion into areas that are the habitat of certain species.

When people clear a forest，some species may be lost.

In the near future，many other extinctions are possible or likely.

In some cases，the problem is due to human greed.

For example，some people buy ivory that is taken from bodies of animals such as elephants or rhinoceros.

Hunters sometimes kill these animals simply to take their ivory，and the result is a tragic decline in populations.

Another example involves bears in North America.

Some people buy the sexual organs of these animals for use as aphrodisiacs or sexual stimulants.

The result is that the hunters kill these animals simply to obtain these organs，and this leads to a reduction in the number of bears.

Fortunately，many countries have laws to prevent the hunting of species that are facing extinction，knowns as “endangered species.

However，some hunting of these endangered animals continues.

Only by refusing to buy the products that are made from endangered species can we prevent this terrible crime.