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.

　　在風風光光慶祝完自己登基60周年后，英國女王伊麗莎白二世（Queen Elizabeth II）現在可以期待打破更多紀錄了。86歲的她已經是英國歷史上最年長的君主了（如果她現在離世，她的兒子就會立即成為第12位年長的君主）。到2015年9月10日，她將會超越維多利亞女王（QueenVictoria），成為英國歷史上在位時間最長的君主。要打敗四歲時繼承王位的路易十四（Louis XIV）成為歐洲歷史上在位時間最長的君主，她需要活到98歲。

　　伊麗莎白二世身體依然很硬朗，但人類最長壽命并不像平均預期壽命一樣在不斷增長，后者在全球范圍內以每年約三個月的幅度在增長，主要是由于對抗過早死亡方面取得的進展。的確，我們或許已經達到了某種最長壽命的極限，這可能是因為嚴格以繁殖成功為中心的自然選擇過程沒有必要特別保存能讓我們活到150歲的基因。

　　根據研究老齡化問題的老年學研究組織（Gerontology Research Group）的數據，世界最長壽的女性、來自佐治亞州的退休教師貝斯·庫珀（Besse Cooper）將在8月26日年滿116歲。這是很長壽的年紀了，但是依然比世界紀錄小六歲多：122歲零164天，它是由法國的雅娜·卡爾芒（JeanneCalment）創下的紀錄。換句話說，如果庫珀能活到這個年紀，那么卡爾芒的紀錄就保持了21年，如果活不到，可能保持的時間會更長。

　　這會是漫長的一段時間，因為目前全世界有近50萬百歲老人在世。這個數字在以每年7%的幅度增長，但115歲以上老人的人數并沒有增加。

　　如果庫珀沒有刷新紀錄，就只有兩位在世的115歲老人接受這項挑戰，其中一位是男性：來自日本京都的退休郵差木村次郎右衛門（Jiroemon Kimura）。他還有七個月就將打破由1998年去世的克里斯蒂安·莫滕森（Christian Mortensen）創下的男性最長壽命紀錄。但木村次郎右衛門活到122歲的可能性沒有女性大，而目前超過115歲的女性（兩位）沒有2006年（四位）多，甚至還不如1997年（三位）。

　　從出生證明來看，19世紀至少有兩個人在110歲生日后逝世。因此，20世紀最長壽命12年的增長幅度只不過是同期平均壽命增幅（36年）的三分之一。

　　2002年，德國羅斯托克馬克斯-普朗克人口研究所（Max Planck Institute for DemographicResearch）的詹姆斯·沃佩爾（James Vaupel）指出，每次公開發布的對平均壽命趨穩水平的估計都會在幾年內被打破，這令人口統計學家感到吃驚。然而，伊利諾伊大學（University of Illinois）的杰伊·奧爾山斯基（Jay Olshansky）則認為，從1980年開始，在美國等富裕國家，這種規律已經不適用于已經進入高齡的老人了：官方對年齡在65歲的女性剩余壽命的估算應該下調。

　　由于生活方式越來越健康，活到高齡的人越來越多。但這與人類壽命存在某種期限并不矛盾。大多數科學家認為，人體隨年齡增大而衰老本身并不是由基因決定的，但延緩衰老的修復機制卻是由基因決定的。對人類來說，幫助人作為父母甚至祖父母活著的基因有助于孩子健壯成長因而具備了選擇性優勢，但幫助人作為曾祖父母活著的基因可能永遠都不會有助于繁殖成功，因為曾祖父母在曾孫的健康和生存上可能發揮不了什么作用。

　　換句話說，活到90歲或100歲者的人數或許沒有上限，但讓一大批人活到120歲以上或許永遠都不可能實現，沒有遺傳工程的幫助，人是很難活到150歲的，即便君主也做不到。