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五单元Effortstocombatagingandextendhumanlifedateatleastasfarbackas3500B.C.,andself-proclaimedexpertshavetoutedanti-agingelixirseversince.Indeed,theprospectofimmortalityhasalwayshaduniversalappeal,spurringAlexandertheGreatandPoncedeLeóntosearchforthelegendaryFountainofYouthandfeedingalchemists'desiretomanufacturegold(oncebelievedtobethemostpotentanti-agingsubstanceinexistence).Butthehawkingofanti-aging“therapies”hastakenaparticularlytroublingturnoflate.Disturbinglylargenumbersofentrepreneursareluringgullibleandfrequentlydesperatecustomersofallagesto“longevity”clinics,claimingascientificbasisfortheanti-agingproductstheyrecommendand,often,sell.Atthesametime,theInternethasenabledthosewhoseeklucrefromsupposedanti-agingproductstonewcustomerswithease.努力与衰老作斗争并延长人类的寿命至少可以追溯到公元前3500年前，从那时起那些自诩的专家就一直兜售抗衰老长生不老药，的确，长生不老一直对人们具有普遍的吸引力，促使亚历山大大帝和庞塞·德·里昂寻找传说中的“青春之泉”，并满足炼金术士们制造黄金的欲望（人们一度认为它是目前最有效的抗衰老物质）。但是抗衰老的兜售方式的转变令人担忧。令人不安的是，大量的企业家都在引诱各个年龄层的易受骗和常常是绝望的顾客去“长寿”诊所，声称他们所推荐的抗衰老产品有科学的依据，并常常把产品卖给他们。与此同时，互联网使那些从所谓的抗衰老产品中寻找利润的人可以轻松地接触到新客户。Alarmedbythesetrends,scientistswhostudyaginghaveissuedapositionstatementcontainingthiswarning:nocurrentlymarketedintervention－none－hasyetbeenprovedtoslow,stoporreversehumanaging,andsomecanbedownrightdangerous.研究老化问题的科学家对这些趋势感到震惊，他们发表了一份立场声明，其中包含了这样的警告：目前还没有市场上的干预措施能够减缓、阻止或逆转人类的衰老，其中一些措施可能是非常危险的。Anydiscussionofagingshouldfirstclarifyitsterms.Variousdefinitionshavebeenproposed,butwethinkofagingastheaccumulationofrandomdamagetothebuildingblocksoflife－especiallytoDNA,certainproteins,carbohydratesandlipids(fats)－thatbeginslifeearlyinlifeandeventuallyexceedsthebody'sself-repaircapabilities.Thisdamagegraduallyimpairsthefunctioningofcells,tissues,organsandorgansystems,therebyvulnerabilitytodiseaseandgivingrisetothecharacteristicmanifestationsofaging,suchasalossofmuscleandbonemass,adeclineinreactiontime,compromisedhearingandvision,andreducedelasticityofskin.任何关于衰老的讨论都应该首先澄清它的术语。人们提出了各种不同的定义，但我们认为衰老是对生命构成要素的随机损伤的积累——特别是对DNA、某些蛋白质、碳水化合物和脂类（脂肪）--这种损伤开始于生命早期，最终超过了身体的自我修复能力。这种损害逐渐损害细胞、组织、器官和器官系统的功能，从而易患病，并导致衰老的典型表现，如肌肉萎缩和骨量疏松，反应时间下降，听力和视力受损，皮肤弹性降低。Aging,inourview,makesusevermoresusceptibletosuchillsasheartdisease,Alzheimer'sdisease,strokeandcancer,buttheseage-relatedconditionsaresuperimposedonaging,notequivalenttoit.Therefore,evenifsciencecouldeliminatetoday'sleadingkillersofolderindividuals,agingwouldcontinuetooccur,ensuringthatdifferentmaladieswouldtaketheirplace.Inaddition,itwouldguaranteethatonecrucialbodycomponentoranother－say,thecardiovascularsystem－wouldeventuallyexperienceacatastrophicfailure.Itisaninescapablebiologicalrealitythatoncetheengineoflifeswitcheson,thebodyinevitablysowstheseedsofitsowndestruction.在我们看来，衰老使我们更易得心脏病、阿尔茨海默病、中风和癌症等疾病，但这些与年龄相关的疾病是衰老带来的附加物，并不等同于衰老。因此，即使科学能够消灭当今导致老年人死亡的主要杀手，衰老也会继续发生，会让不同的疾病取代他们。此外，衰老也会让人体的某个或几个重要的组成部分-比如心血管系统，最终会经历一场灾难性的失败。这是一个不可避免的生物现实，一旦生命的引擎启动，身体就不可避免地播下自我毁灭的种子。Menandwomeninthedevelopedworldtypicallylivelongernow(75and80years,respectively)thantheydidthroughoutmuchofhistory(about25years)becausehumaningenuity－whichbroughtussanitationsystems,vaccines,antibioticsandsoon－hashadphenomenalsuccessinthwartingtheinfectiousandparasiticdiseasesresponsibleforagreatdealofprematuredeath.Welivelongernownotbecausewehavealteredthewayweagebutbecausewehavealteredthewaywelive.发达国家的男性和女性通常比他们在整个历史（大约25年）中活得更久（分别为75岁和80岁），因为人类的智慧，卫生系统、疫苗、抗生素等为我们带来了非凡的成功，阻止了传染病和寄生虫引起的疾病带来的大量的早逝。我们现在的寿命更长，不是因为改变了衰老的方式，而是因为我们改变了我们的生活方式。Thoughinevitable,agingisnot,assomemightthink,ageneticallyprogrammedprocess,playingitselfoutonarigidlypredeterminedtimeschedule.Thewayevolutionworksmakesitimpossibleforustopossessgenesthatarespecificallydesignedtocausephysiologicaldeclinewithageortocontrolhowlongwelive.Justasanautomobiledoesnothaveabuilt-inplanfordeclinewritteninitsblueprints,wedonotpossessgeneticintructionsthattellourbodieshowtoageorwhentodie.虽然衰老是不可避免的，但衰老并不是一些人所认为的那样，一个基因编程的过程，而是按照预定的时间表执行的。进化的方式使得我们不可能拥有特定设计的基因，这些基因会随着年龄的增长而引起生理上的衰退，或者控制我们的寿命。就像汽车蓝图中没有内置的衰退计划一样，我们也没有基因指令告诉我们的身体如何衰老或何时死亡。Withoutadoubt,ahostofourgenesinfluenceaging,buttheydosoindirectly,asaninadvertentby-productofprocessesinvolvedingrowth,development,andthemaintenanceofhealthandvigor.Thelackofaspecificgeneticprogramforaginganddeathmeansthattherearenoquickfixesthatwillpermitustotreatagingasifitwereadisease.Asinglegeneticinterventioninanorganismascomplexasahumanbeingwouldhavelittlechanceofcombatingtheprobablyvastarrayofgenesandbiologicalactivitiesthatplaysubtle,unpredictablepartinthetimingofourultimatedemise.毫无疑问，我们的很多基因都会影响衰老，但它们是间接的，是生长、发育、保持健康和活力过程中的副产品。缺乏针对衰老和死亡的特定基因计划意味着，我们没有快速的解决办法，可以把衰老当作一种疾病来对待。对一个像人类这样复杂的有机体进行单一的基因干预，就几乎没有机会与在我们最终灭亡的时间安排中扮演微妙、不可预测角色的大量基因和生物活动作斗争。Onwhatgroundsdoweassertsovehementlythatnopurpotedanti-aginginterventionhasbeenprovedtomodifyaging?Toassesswhetheraninterventionhasaffectedabiologicalprocess,researchersneedayardstickformeasuringthatprocess.Inthiscase,nosingleoraggregateage-relatedphenomenonhasprovedtobeareliableindicatoroftherateofaginginhumansorotherspecies.Withoutayardstick,therecanbenoassurancethataninterven