When it comes to the human responsiblity for conservation of the endangered species, controversy is always inevitable. Some would argue that  society is in duty bound to saving every plant and animal species, however the expense.Others hold the opposite view that such efforts, especially at a great cost in money and jobs, to save endangered species is not of necessity. On balance, I  tend more colsely to incline with the former notion.     It might be tempting to believe that extinction results from the process of the so-called "natural selection" suggested by Darwin in which that stronger species survive while the weaker ones do not. This argument implies that the extinction is only due to the mother nature, we human beings, on the other hand, have no particular obligation to pay nature's debt. Furthermore, as one kind of species, human does not make an exception of the  process, as we are only behaving as animal's must.    However, at the heart of this argument lies a certain coldness and lack of compassion. As the dominant species of the planet, aren't we supposed to act like the elder brother in the family who'd always look after his younger brother? In addition, does extinction bear no relationship on humankind? Admittedly, there has been 75 species become extinct every day, at the rate of 4 species per hour, even before humankind exists. Whereas,most of the species exinction from 1000 AD to 2000 AD are owing to certain human activities, in particular destruction of plant and animal habitats, let alone other damaging side-effects of economic growth and development.     Those who accede the latter point may also argue that it is far beyond our capability to save all the endangered species, which include literally hundreds of millions kinds. Thus, we are inclined to favor the ones that serve as medicines or industrial materials for our own economic interest. In other words, the more money and jobs it would cost to save a certain species, the lower  priority we should place on doing so.     Although the proposition "saving the cheap species only" appeared to be warranted, not everything is as it seems. In this case, the certain conception "cheap species" may need to be redefined, considering the intrinsic value and the essential significance of the biodiversity. Biodiversity, comprised from genetic diversity, species diversity and ecosystem diversity, is not only beneficial, but indispensable to our living condition. Once it decreased to a certain amount, the balance of the food-chain, as well as of the material recycling and energy conversion would be severely striked, which eventually leads to the extinction of all of us, without appropriate measures to be taken. From this point of view, nealy all species is equivalent in maintaining the biodiversity. Accordingly, a species is neither cheaper nor more costly than another.     In the final analysis, it is our society's responsiblity to save endangered species as much as we could, however the cost. While we are more willing to believe that we are not the source of their pain, well, as discussed above, it is partly our fault. And our conscience keeps warning us that we cannot turn a blind eye to the weak. Moreover, although the process of saving would cost a fortune, the money is worth it if we regard it as a means to saving our own lives by preserving the biodiversity which serves our best interests in the long run.   
      注：我是10月23号的新G，这是第一次完整写一篇ISSUE.. 严重超时。。感觉斟酌言辞用时过长，还有许多词汇不知如何合适表达，写作过程中也有查阅字典或参考句子。 现在作文放在最先了，应该对心态影响比较大，不知怎样提速。。望指导。。谢谢！