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.

　　在风风光光庆祝完自己登基60周年后，英国女王伊丽莎白二世（Queen Elizabeth II）现在可以期待打破更多纪录了。86岁的她已经是英国历史上最年长的君主了（如果她现在离世，她的儿子就会立即成为第12位年长的君主）。到2015年9月10日，她将会超越维多利亚女王（QueenVictoria），成为英国历史上在位时间最长的君主。要打败四岁时继承王位的路易十四（Louis XIV）成为欧洲历史上在位时间最长的君主，她需要活到98岁。

　　伊丽莎白二世身体依然很硬朗，但人类最长寿命并不像平均预期寿命一样在不断增长，后者在全球范围内以每年约三个月的幅度在增长，主要是由于对抗过早死亡方面取得的进展。的确，我们或许已经达到了某种最长寿命的极限，这可能是因为严格以繁殖成功为中心的自然选择过程没有必要特别保存能让我们活到150岁的基因。

　　根据研究老龄化问题的老年学研究组织（Gerontology Research Group）的数据，世界最长寿的女性、来自佐治亚州的退休教师贝斯·库珀（Besse Cooper）将在8月26日年满116岁。这是很长寿的年纪了，但是依然比世界纪录小六岁多：122岁零164天，它是由法国的雅娜·卡尔芒（JeanneCalment）创下的纪录。换句话说，如果库珀能活到这个年纪，那么卡尔芒的纪录就保持了21年，如果活不到，可能保持的时间会更长。

　　这会是漫长的一段时间，因为目前全世界有近50万百岁老人在世。这个数字在以每年7%的幅度增长，但115岁以上老人的人数并没有增加。

　　如果库珀没有刷新纪录，就只有两位在世的115岁老人接受这项挑战，其中一位是男性：来自日本京都的退休邮差木村次郎右卫门（Jiroemon Kimura）。他还有七个月就将打破由1998年去世的克里斯蒂安·莫滕森（Christian Mortensen）创下的男性最长寿命纪录。但木村次郎右卫门活到122岁的可能性没有女性大，而目前超过115岁的女性（两位）没有2006年（四位）多，甚至还不如1997年（三位）。

　　从出生证明来看，19世纪至少有两个人在110岁生日后逝世。因此，20世纪最长寿命12年的增长幅度只不过是同期平均寿命增幅（36年）的三分之一。

　　2002年，德国罗斯托克马克斯-普朗克人口研究所（Max Planck Institute for DemographicResearch）的詹姆斯·沃佩尔（James Vaupel）指出，每次公开发布的对平均寿命趋稳水平的估计都会在几年内被打破，这令人口统计学家感到吃惊。然而，伊利诺伊大学（University of Illinois）的杰伊·奥尔山斯基（Jay Olshansky）则认为，从1980年开始，在美国等富裕国家，这种规律已经不适用于已经进入高龄的老人了：官方对年龄在65岁的女性剩余寿命的估算应该下调。

　　由于生活方式越来越健康，活到高龄的人越来越多。但这与人类寿命存在某种期限并不矛盾。大多数科学家认为，人体随年龄增大而衰老本身并不是由基因决定的，但延缓衰老的修复机制却是由基因决定的。对人类来说，帮助人作为父母甚至祖父母活着的基因有助于孩子健壮成长因而具备了选择性优势，但帮助人作为曾祖父母活着的基因可能永远都不会有助于繁殖成功，因为曾祖父母在曾孙的健康和生存上可能发挥不了什么作用。

　　换句话说，活到90岁或100岁者的人数或许没有上限，但让一大批人活到120岁以上或许永远都不可能实现，没有遗传工程的帮助，人是很难活到150岁的，即便君主也做不到。