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  3. Why do animals grow old and die at characteristic ages? Even if maintained in peak condition and not eaten by your cat, your ham

Why do animals grow old and die at characteristic ages? Even if maintained in peak condition and not eaten by your cat, your ham

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问题    Why do animals grow old and die at characteristic ages? Even if maintained in peak condition and not eaten by your cat, your hamster is unlikely to make it much past its second birthday. And your cat might live for ten times that. Yet neither cat nor hamster will ever match the average healthy human for longevity.
   A study uses demographic data to reveal a lifespan that human beings cannot exceed. It’s like running. 【F1】Elite athletes might shave a few milliseconds off the world record for the 100-metre race, but they’ll never run the same distance in, say, five seconds, or two. Human beings are simply not made that way. The same is true for longevity. 【F2】The consequences of numerous factors related to our genetics, metabolism, reproduction and development, all shaped over millions of years of evolution, means that few humans will make it past their 120th birthdays.
   Maximum lifespan is a bald measure of years accumulated. It is not the same as life expectancy, which is an actuarial measure of how long one is expected to live from birth, or indeed from any given age. 【F3】Life expectancy at birth has increased in most countries over the past century, not because people have longer lifespans, but mainly because infectious disease does not kill as many infants as it once did.
   【F4】So if we owe our increases in life expectancy to better public health, nutrition, sanitation and vaccination, is it not fair to ask whether more-effective treatments for diseases such as cancer, Parkinson’s disease and Alzheimer’s might also yield dividends in maximum lifespan? Will 120th birthday parties become routine, outmatched by a small yet increasing number of sesquicentenarians? The demographic data say no. People are living longer, and the population as a whole is greying, but the rate of increase in the number of centenarians is slowing, and might even have peaked.
   Could it be possible, in some science-fictional future, to break free from the bonds of human life expectancy and increase lifespan indefinitely? Technological solutions might one day transcend the limitations of the human body. But the risks of transcendence are twofold. 【F5】First, it might be that to extend our lives beyond our normal span, we must somehow become other than human. After all, what would a 50-year-old hamster be like? Second, there is a risk that life wouldn’t really be that much longer—it would only feel like it.
【F2】
选项
答案这是人类基因、新陈代谢、生殖和发育经由几百万年的进化演变，受到无数因素影响而得出的结论：鲜有人能活到120岁。
解析 ①本句是复合句。介词短语of numerous factors修饰主句主语，表示“多种因素带来的结果”。②主句主语后有两个过去分词短语充当的后置定语，第一个是related to our…and development，意为“与人类基因、新陈代谢、生殖和发育有关”。第二个是all shaped over millions of years of evolution，意为“由几百万年的进化演变而成”。③宾语从句包含“make+宾语+宾补”的结构，意思是使宾语变成宾补所描述的那样。此处it指代的是前文的longevity，意为“人类的寿命不能长于……”。
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