《A Short History of Nearly Everything》第131章

lly　through　the　pus　in　surgicalbandages；　miescher　found　a　substance　he　didn’t　recognize　and　called　it　nuclein　（because　itresided　in　the　nuclei　of　cells）。　at　the　time；　miescher　did　little　more　than　note　its　existence；　butnuclein　clearly　remained　on　his　mind；　for　twenty…three　years　later　in　a　letter　to　his　uncle　heraised　the　possibility　that　such　molecules　could　be　the　agents　behind　heredity。　this　was　anextraordinary　insight；　but　one　so　far　in　advance　of　the　day’s　scientific　requirements　that　itattracted　no　attention　at　all。
for　most　of　the　next　half　century　the　mon　assumption　was　that　the　material—nowcalled　deoxyribonucleic　acid；　or　dna—had　at　most　a　subsidiary　role　in　matters　of　heredity。　itwas　too　simple。　it　had　just　four　basic　ponents；　called　nucleotides；　which　was　like　havingan　alphabet　of　just　four　letters。　how　could　you　possibly　write　the　story　of　life　with　such　arudimentary　alphabet？　（the　answer　is　that　you　do　it　in　much　the　way　that　you　create　plexmessages　with　the　simple　dots　and　dashes　of　morse　code—by　bining　them。）　dna　didn’tdo　anything　at　all；　as　far　as　anyone　could　tell。　it　just　sat　there　in　the　nucleus；　possibly　bindingthe　chromosome　in　some　way　or　adding　a　splash　of　acidity　on　mand　or　fulfilling　someother　trivial　task　that　no　one　had　yet　thought　of。　the　necessary　plexity；　it　was　thought；had　to　exist　in　proteins　in　the　nucleus。
there　were；　however；　two　problems　with　dismissing　dna。　first；　there　was　so　much　of　it：
two　yards　in　nearly　every　nucleus；　so　clearly　the　cells　esteemed　it　in　some　important　way。　ontop　of　this；　it　kept　turning　up；　like　the　suspect　in　a　murder　mystery；　in　experiments。　in　twostudies　in　particular；　one　involving　the　pneumonococcus　bacterium　and　another　involvingbacteriophages　（viruses　that　infect　bacteria）；　dna　betrayed　an　importance　that　could　only　beexplained　if　its　role　were　more　central　than　prevailing　thought　allowed。　the　evidencesuggested　that　dna　was　somehow　involved　in　the　making　of　proteins；　a　process　vital　to　life；yet　it　was　also　clear　that　proteins　were　being　made　outside　the　nucleus；　well　away　from　thedna　that　was　supposedly　directing　their　assembly。
no　one　could　understand　how　dna　could　possibly　be　getting　messages　to　the　proteins。　theanswer；　we　now　know；　was　rna；　or　ribonucleic　acid；　which　acts　as　an　interpreter　betweenthe　two。　it　is　a　notable　oddity　of　biology　that　dna　and　proteins　don’t　speak　the　samelanguage。　for　almost　four　billion　years　they　have　been　the　living　world’s　great　double　act；　andyet　they　answer　to　mutually　inpatible　codes；　as　if　one　spoke　spanish　and　the　other　hindi。
to　municate　they　need　a　mediator　in　the　form　of　rna。　working　with　a　kind　of　chemicalclerk　called　a　ribosome；　rna　translates　information　from　a　cell’s　dna　into　terms　proteinscan　understand　and　act　upon。
however；　by　the　early　1900s；　where　we　resume　our　story；　we　were　still　a　very　long　wayfrom　understanding　that；　or　indeed　almost　anything　else　to　do　with　the　confused　business　ofheredity。
clearly　there　was　a　need　for　some　inspired　and　clever　experimentation；　and　happily　the　ageproduced　a　young　person　with　the　diligence　and　aptitude　to　undertake　it。　his　name　wasthomas　hunt　morgan；　and　in　1904；　just　four　years　after　the　timely　rediscovery　of　mendel’sexperiments　with　pea　plants　and　still　almost　a　decade　before　gene　would　even　bee　a　word；he　began　to　do　remarkably　dedicated　things　with　chromosomes。
chromosomes　had　been　discovered　by　chance　in　1888　and　were　so　called　because　theyreadily　absorbed　dye　and　thus　were　easy　to　see　under　the　microscope。　by　the　turn　of　thetwentieth　century　it　was　strongly　suspected　that　they　were　involved　in　the　passing　on　of　traits；but　no　one　knew　how；　or　even　really　whether；　they　did　this。
morgan　chose　as　his　subject　of　study　a　tiny；　delicate　fly　formally　called　drosophilamelanogaster；　but　more　monly　known　as　the　fruit　fly　（or　vinegar　fly；　banana　fly；　orgarbage　fly）。　drosophila　is　familiar　to　most　of　us　as　that　frail；　colorless　insect　that　seems　tohave　a　pulsive　urge　to　drown　in　our　drinks。　as　laboratory　specimens　fruit　flies　had　certainvery　attractive　advantages：　they　cost　almost　nothing　to　house　and　feed；　could　be　bred　by　themillions　in　milk　bottles；　went　from　egg　to　productive　parenthood　in　ten　days　or　less；　and　hadjust　four　chromosomes；　which　kept　things　conveniently　simple。
working　out　of　a　small　lab　（which　became　known　inevitably　as　the　fly　room）　inschermerhorn　hall　at　columbia　university　in　new　york；　morgan　and　his　team　embarked　ona　program　of　meticulous　breeding　and　crossbreeding　involving　millions　of　flies　（onebiographer　says　billions；　though　that　is　probably　an　exaggeration）；　each　of　which　had　to　becaptured　with　tweezers　and　examined　under　a　jeweler’s　glass　for　any　tiny　variations　ininheritance。　for　six　years　they　tried　to　produce　mutations　by　any　means　they　could　think　of—zapping　the　flies　with　radiation　and　x…rays；　rearing　them　in　bright　light　and　darkness；　bakingthem　gently　in　ovens；　spinning　them　crazily　in　centrifuges—but　nothing　worked。　morgan　wason　the　brink　of　giving　up　when　there　occurred　a　sudden　and　repeatable　mutation—a　fly　thathad　white　eyes　rather　than　the　usual　red　ones。　with　this　breakthrough；　morgan　and　hisassistants　were　able　to　generate　useful　deformities；　allowing　them　to　track　a　trait　throughsuccessive　generations。　by　such　means　they　could　work　out　the　correlations　betweenparticular　characteristics　and　individual　chromosomes；　eventually　proving　to　more　or　lesseveryone’s　satisfaction　that　chromosomes　were　at　the　heart　of　inheritance。
the　problem；　however；　remained　the　next　level　of　biological　intricacy：　the　enigmatic　genesand　the　dna　that　posed　them。　these　were　much　trickier　to　isolate　and　understand。　aslate　as　1933；　when　morgan　was　awarded　a　nobel　prize　for　his　work；　many　researchers　stillweren’t　convinced　that　genes　even　existed。　as　morgan　noted　at　the　time；　there　was　noconsensus　“as　to　what　the　genes　are—whether　they　are　real　or　purely　fictitious。”　it　may　seemsurprising　that　scientists　could　struggle　to　accept　the　physical　reality　of　something　sofundamental　to　cellular　activity；　but　as　wallace；　king；　and　sanders　point　out　in　biology：　thescience　of　life　（that　rarest　thing：　a　readable　college　text）；　w