近年来常常听到有物种灭绝的消息，令人担忧。有渡渡鸟，有扬子鳄等。一度大熊猫也是濒危品种，而中国政府投入大量资金对其进行了保护。那么，我们是否应该不记成本地去挽救那些濒危物种呢？Recently, news about extinction of species could always be heard, worryingly creating many ecology . Dodo birds, Yangtze alligators. Giant panda, somehow a symbol of China, once nearly extinct, was saved by Chinese government by fiscal funds. The problem is, should we save the species, despite the expense to humans in effort, time, and financial well-being? In my opinion, for the endangered species that was died out of human activities, we should save them at the cost that less than the damage it would cause. Otherwise we can use the resources to do something else, such as compensate the extinction of the species--if it costs less expense. 
The famous extinct species called Dodo bird, used to live in Madagascar, was died out of human's incontinent slaughter. It was a misery itself, what's more, the extinction of Dodo bird triggered an extinction of a kind of tree. The tree could only use the stomach of Dodo to transfer their seeds. An scientist discovered this and they finally found another kind of bird to take place of Dodo.
At the very beginning of the development of Australia, people found that a kind of deer in an area were prey of wolves. To protecting the deers, their prey, people killed most of the wolves, they almost extinct. However, they found that the deer began to have baby boom, and the population of deer increased incredibly, finally this surge create an severe damage to the prairie, with an unexpected desertification.    
We can see that the consequence of the extinction of species is a huge problem of the ecosystem. Since it is always human activities that caused those problems, we have the responsibility to solve the problems. But should we save the endangered species despite the costs? I think it would be a wise way to compare the damage that the extinction would cause and the costs to protect the species. Since the damages are always big enough, and sometimes unexpected, it is alway necessary to save them.
In the first example that I gave, native people finally called the wolves back to prairie, which brought everything into balance again. In the second example, scientists finally find another kind of bird to replace Dodo, which can also bring the trees' seeds, saved them out of danger finally. We have the obligation to compensate the mistakes that we made. However, sometimes it is useless to save the endangered species regardless of how much the cost would be. We have to make sure that the live of species must deserve the effort that we made. Otherwise, it would also be a kind of waste of humans in effort, money and time.
However, as I said at the beginning, we should consider that some species are died out of natural selection. For example, dinosaur. It cannot live after the huge collision of an asteroid, was another kind of natural selection. Except to dinosaur, there are much more species died because of incapability of natural changes slowly, at a speed that cannot easily discovered by human beings.  In that case, this species is not needed in the ecosystem any more, accordingly, we have no responsibility to save them.
In conclusion, we should save all the endangered species that are going to die out because of human activities. But we'd better compare the cost and the impending damage to make to decision.