As is shown by the two graphs,the U.S. population soared from 2 million to 250 million from 1800 to
1990.In contrast,the number of wildlife species no longer existing shot up,adding up to 70 over the
same period of time.It is obvious that the extinction of wildlife resulted from the population
explosion.We may cite a variety of reasons for this situation.First of all,the destruction of
ecological balance plays a pushing role.Due to the population problems,pollution and desertification
are becoming increasingly serious.Furthermore,a great number of species were killed for food,for
money and even for fun.Even worse,with the rapid growth of human population,inhabitable areas were
expanding so fast that few areas were left for wild animals.To sum up,it is imperative for us to
take effective measures to protect wildlife.Firstly,the U.S. government should pour more investment
into wildlife protection in a bid to create a better environment.Secondly,the birth rate in the U.S
. must be put under control as the dramatically expending population gives rise to serious
environmnet problesm.