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本帖最后由 DR.J 于 2015-11-5 15:25 编辑
Do Human Beings Carry Expiration Dates?
After celebrating her 60th year on the throne in style this pastweek, Britain's Queen Elizabeth II can now look forward tobreaking some more records. She is already, at 86, Britain'soldest monarch (were she to die now, her son wouldimmediately be the 12th oldest). On Sept. 10, 2015, she wouldpass Queen Victoria to become the longest-reigning monarch inBritish history. To beat Louis XIV (who succeeded to the throneat the age of 4) for the longest reign in European history, she would have to live to 98.
Elizabeth II is still going strong, but the maximum human lifespan isn't rising at anything like therate of average life expectancy, which is rushing upward globally at the rate of about three monthsa year, mainly because of progress against premature mortality. Indeed, we may already have hitsome kind of limit for maximum lifespan -- perhaps because natural selection, with its strict focus onreproductive success, has no particular need to preserve genes that would keep us going to 150.
The oldest woman in the world, Besse Cooper, a retired schoolteacher in Georgia, will be 116 onAug. 26, according to the Gerontology Research Group, an organization that studies aging issues. That's a great age, but it's a hefty six years short of the record: 122 years and 164 days, set byJeanne Calment of France in 1997. In other words, if Mrs. Cooper can get there, Mrs. Calment'srecord will have stood for 21 years; if she can't, maybe longer.
That's a long time, considering that there are now nearly a half million centenarians alive in theworld. That number has been going up 7% a year, but the number of those over 115 is notincreasing.
If Mrs. Cooper does not take the record, there are only two other 115-year-olds alive to take onthe challenge, and one of them is a man: Jiroemon Kimura, a retired postman from Kyoto. He'swithin seven months of beating the age record for his sex, set by Christian Mortensen, who died in 1998. But Mr. Kimura is less likely than a woman to make 122, and there are fewer women over 115 today (two) than there were in 2006 (four) or even 1997 (three).
At least two people died after their 110th birthdays in the 1800s, if you're willing to trust the birthcertificates. So the increase of 12 years in maximum life expectancy during the 20th century wasjust one-third as large as the increase in average life expectancy during the period (36 years).
In 2002, James Vaupel of the Max Planck Institute for Demographic Research in Rostock, Germany, startled demographers by pointing out that every estimate published of the level atwhich average life expectancy would level out has been broken within a few years. Jay Olshanskyof the University of Illinois, however, argues that since 1980 this has no longer been true foralready-old people in rich countries like the U.S.: Official estimates of remaining years of life for awoman aged 65 should be revised downward.
Thanks to healthier lifestyles, more and more people are surviving into old age. But that is notincompatible with there being a sort of expiration date on human lifespan. Most scientists think thedecay of the body by aging is not itself programmed by genes, but the repair mechanisms thatdelay decay are. In human beings, genes that help keep you alive as a parent or even grandparenthave had a selective advantage through helping children thrive, but ones that keep you alive as agreat-grandparent -- who likely doesn't play much of a role in the well-being and survival of great-grandchildren -- have probably never contributed to reproductive success.
In other words, there is perhaps no limit to the number of people who can reach 90 or 100, butgetting more than a handful of people past 120 may never be possible, and 150 is probablyunattainable, absent genetic engineering -- even for a monarch.
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