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2003年5月的一天，有人从浏阳河里捞出一只全身金黄色的“金蛤蟆”，据专家证实它的身份是分布于非洲的“爪蟾”。它的偷渡引起了人们的广泛关注，物种入侵不可大意。外来物种的入侵曾使我国蒙受过巨大损失，例如：我国曾经从美国、古巴大规模引进牛蛙，由于牛蛙的寿命长，其食性广泛且食量大，从昆虫到其他小型无脊椎动物无所不吃，繁殖能力强，具有明显的竞争优势，很快泛滥成灾，危害了本地两栖类的生存和发展。
(1)造成牛蛙泛滥成灾的主要原因是什么？__________________。
(2)从生态系统的稳定性方面考虑，人类从不同区域引入新物种时应注意什么？___________________。
(1)牛蛙缺乏天敌的制约。
(2)要对引入的新物种是否会对当地造成生态入侵进行评估，在引进新的物种时还应该引入它的天敌以形成食物链，从而维护当地生态系统的稳定性。
| It looks unlikely that medical science will abolish the process of ageing. But it no longer looks impossible. "In the long run," as John Maynard Keynes observed, "we are all dead." True. But can the short run be elongatedin a way that makes the long run longer And if so, how, and at what cost People have dreamt of immorality since ancient times. Now, with the growth of biological knowledge that has marked the past few decades, a few researchers believe it might be within reach. To think about the question, it is important to understand why organisms — people included —age in the first place. People are like machines, they wear out. That much is obvious. However, a machine can always be repaired. A good mechanic with a stock of spare parts can keep it going indefinitely. Eventually, no part of the original may remain, but it still carries on, like Lincoln’s famous axe that had three new handles and two new blades. The question, of course, is whether the machine is worth repairing. It is here that people and nature disagree. Or, to put it slightly differently, two bits of nature disagree with each other. From the individual’s point of view, survival is an imperative. A fear of death is a sensible evolved response and, since ageing is a sure way of dying, it is no surprise that people want to stop it in its tracks. Moreover, even the appearance of ageing can be harmful. It reduces the range of potential sexual partners who find you attractive and thus, again, curbs your reproduction. The paradox is that the individual’s evolved desire not to age is opposed by another evolutionary force, the disposable soma. The soma is all of a body’s cells apart from the sex cells. The soma’s role is to get those sex cells, and thus the organism’s genes, into the next generation. If the soma is a chicken, then it really is just an egg’s way of making another egg. And if evolutionary logic requires the soma to age and die in order for this to happen, so be it. Which is a pity, for evolutionary logic does, indeed, seem to require that. The argument is this. All organisms are going to die of something eventually. That something may be an accident, a fight, a disease or an encounter with a hungry predator. There is thus a premium on reproducing early rather than conserving resources for a future that may never come. The reason why repairs are not perfect is that they are costly and resources invested in them might be used for reproduction instead. Often, therefore, the body’s mechanics prefer lash-ups to complete rebuilds — or simply do not bother with the job at all. And if that is so, the place to start looking for longer life is in the repair shop. |
It is implied in the passage that ______ .
A．( people put a premium on youth and physical appearance
B．( death is treated as a matter of course
C．( evolutionary force makes immortality possible
D．( reproduction is a useful alternative to longer life