A Short History of Nearly Everything-第89章

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；　the　technique　perfected　by　linus　pauling。

crystallography　had　been　used　successfully　to　map　atoms　in　crystals　（hence“crystallography”）；　but　dna　molecules　were　a　much　more　finicky　proposition。　only　franklinwas　managing　to　get　good　results　from　the　process；　but　to　wilkins’s　perennial　exasperationshe　refused　to　share　her　findings。

if　franklin　was　not　warmly　forthing　with　her　findings；　she　cannot　be　altogetherblamed。　female　academics　at　king’s　in　the　1950s　were　treated　with　a　formalized　disdain　thatdazzles　modern　sensibilities　（actually　any　sensibilities）。　however　senior　or　acplished；they　were　not　allowed　into　the　college’s　senior　mon　room　but　instead　had　to　take　theirmeals　in　a　more　utilitarian　chamber　that　even　watson　conceded　was　“dingily　pokey。”　on　topof　this　she　was　being　constantly　pressed—at　times　actively　harassed—to　share　her　results　witha　trio　of　men　whose　desperation　to　get　a　peek　at　them　was　seldom　matched　by　more　engagingqualities；　like　respect。　“i’m　afraid　we　always　used　to　adopt—let’s　say　a　patronizing　attitudetoward　her；”　crick　later　recalled。　two　of　these　men　were　from　a　peting　institution　and　thethird　was　more　or　less　openly　siding　with　them。　it　should　hardly　e　as　a　surprise　that　shekept　her　results　locked　away。

that　wilkins　and　franklin　did　not　get　along　was　a　fact　that　watson　and　crick　seem　to　haveexploited　to　their　benefit。　although　crick　and　watson　were　trespassing　rather　unashamedlyon　wilkins’s　territory；　it　was　with　them　that　he　increasingly　sided—not　altogether　surprisinglysince　franklin　herself　was　beginning　to　act　in　a　decidedly　queer　way。　although　her　resultsshowed　that　dna　definitely　was　helical　in　shape；　she　insisted　to　all　that　it　was　not。　towilkins’s　presumed　dismay　and　embarrassment；　in　the　summer　of　1952　she　posted　a　mocknotice　around　the　king’s　physics　department　that　said：　“it　is　with　great　regret　that　we　have　toannounce　the　death；　on　friday　18th　july　1952　of　d。n。a。　helix。　。　。　。　it　is　hoped　that　dr。　m。h。f。

wilkins　will　speak　in　memory　of　the　late　helix。”

the　oute　of　all　this　was　that　in　january　1953；　wilkins　showed　watson　franklin’simages；　“apparently　without　her　knowledge　or　consent。”　it　would　be　an　understatement　to　callit　a　significant　help。　years　later　watson　conceded　that　it　“was　the　key　event　。　。　。　it　mobilizedus。”　armed　with　the　knowledge　of　the　dna　molecule’s　basic　shape　and　some　importantelements　of　its　dimensions；　watson　and　crick　redoubled　their　efforts。　everything　now　seemedto　go　their　way。　at　one　point　pauling　was　en　route　to　a　conference　in　england　at　which　hewould　in　all　likelihood　have　met　with　wilkins　and　learned　enough　to　correct　themisconceptions　that　had　put　him　on　the　wrong　line　of　inquiry；　but　this　was　the　mccarthy　eraand　pauling　found　himself　detained　at　idlewild　airport　in　new　york；　his　passport　confiscated；on　the　grounds　that　he　was　too　liberal　of　temperament　to　be　allowed　to　travel　abroad。　crickand　watson　also　had　the　no　less　convenient　good　fortune　that　pauling’s　son　was　working　atthe　cavendish　and　innocently　kept　them　abreast　of　any　news　of　developments　and　setbacks　athome。

still　facing　the　possibility　of　being　trumped　at　any　moment；　watson　and　crick　appliedthemselves　feverishly　to　the　problem。　it　was　known　that　dna　had　four　chemical1in　1968；　harvard　university　press　canceled　publication　of　the　double　helix　after　crick　and　wilkinsplained　about　its　characterizations；　which　the　science　historian　lisa　jardine　has　described　as　〃gratuitouslyhurtful。〃　the　descriptions　quoted　above　are　after　watson　softened　his　ments。

ponents—called　adenine；　guanine；　cytosine；　and　thiamine—and　that　these　paired　up　inparticular　ways。　by　playing　with　pieces　of　cardboard　cut　into　the　shapes　of　molecules；　watsonand　crick　were　able　to　work　out　how　the　pieces　fit　together。　from　this　they　made　a　meccano…like　model—perhaps　the　most　famous　in　modern　science—consisting　of　metal　plates　boltedtogether　in　a　spiral；　and　invited　wilkins；　franklin；　and　the　rest　of　the　world　to　have　a　look。

any　informed　person　could　see　at　once　that　they　had　solved　the　problem。　it　was　withoutquestion　a　brilliant　piece　of　detective　work；　with　or　without　the　boost　of　franklin’s　picture。

the　april　25；　1953；　edition　of　nature　carried　a　900…word　article　by　watson　and　crick　titled“a　structure　for　deoxyribose　nucleic　acid。”　acpanying　it　were　separate　articles　bywilkins　and　franklin。　it　was　an　eventful　time　in　the　world—edmund　hillary　was　just　about　toclamber　to　the　top　of　everest　while　elizabeth　ii　was　imminently　to　be　crowned　queen　ofengland—so　the　discovery　of　the　secret　of　life　was　mostly　overlooked。　it　received　a　smallmention　in　the　news　chronicle　and　was　ignored　elsewhere。

rosalind　franklin　did　not　share　in　the　nobel　prize。　she　died　of　ovarian　cancer　at　the　age　ofjust　thirty…seven　in　1958；　four　years　before　the　award　was　granted。　nobel　prizes　are　notawarded　posthumously。　the　cancer　almost　certainly　arose　as　a　result　of　chronic　overexposureto　x…rays　through　her　work　and　needn’t　have　happened。　in　her　much…praised　2002　biographyof　franklin；　brenda　maddox　noted　that　franklin　rarely　wore　a　lead　apron　and　often　steppedcarelessly　in　front　of　a　beam。　oswald　avery　never　won　a　nobel　prize　either　and　was　alsolargely　overlooked　by　posterity；　though　he　did　at　least　have　the　satisfaction　of　living　just　longenough　to　see　his　findings　vindicated。　he　died　in　1955。

watson　and　crick’s　discovery　wasn’t　actually　confirmed　until　the　1980s。　as　crick　said　inone　of　his　books：　“it　took　over　twenty…five　years　for　our　model　of　dna　to　go　from　being　onlyrather　plausible；　to　being　very　plausible　。　。　。　and　from　there　to　being　virtually　certainlycorrect。”

even　so；　with　the　structure　of　dna　understood　progress　in　genetics　was　swift；　and　by　1968the　journal　science　could　run　an　article　titled　“that　was　the　molecular　biology　that　was；”

suggesting—it　hardly　seems　possible；　but　it　is　so—that　the　work　of　genetics　was　nearly　at　anend。

in　fact；　of　course；　it　was　only　just　beginning。　even　now　there　is　a　great　deal　about　dna　thatwe　scarcely　understand；　not　least　why　so　much　of　it　doesn’t　actually　seem　to　do　anything。

ninety…seven　percent　of　your　dna　consists　of　nothing　but　long　stretches　of　meaninglessgarble—“junk；”　or　“non…coding　dna；”　as　biochemists　prefer　to　put　it。　only　here　and　therealong　each　strand　do　you　find　sections　that　control　and　organize　vital　functions。　these　are　thecurious　and　long…elusive　genes。

genes　are　nothing　more　（nor　less）　than　instructions　to　make　proteins。　this　they　do　with　acertain　dull　fidelity。　in　this　sense；　they　are　rather　like　the　keys　of　a　piano；　each　playing　asingle　note　and　nothing　else；　which　is　obviously　a　trifle　monotonous。　but　bine　the　genes；as　you　would　bine　piano　keys；　and　you　can　create　chords　and　melodies　of　infinite　variety。

put　all　these　genes　together；　and　you　have　（to　continue　the　metaphor）　the　great　symphony　ofexistence　known　as　the　human　genome。

an　alternative　and　more　mon　way　to　regard　the　genome　is　as　a　kind　of　instructionmanual　for　the　body。　viewed　this　way；　the　chromosomes　can　be　imagined　as　the　book’schapters　and　the　genes　as　individual　instructions　for　making　proteins。　the　words　in　which　theinstructions　are　written　are　called　codons；　and　the　letters　are　known　as　bases。　the　bases—theletters　of　the　genetic　alphabet—consist　of　the　four　nucleotides　mentioned　a　page　or　two　back：

adenine；　thiamine；　guanine；　and　cytosine。　despite　the　importance　of　what　they　do；　thesesubstances　are　not　made　of　anything　exotic。　guanine；　for　instance；　is　the　same　stuff　thatabounds　in；　and　gives　its　name　to；　guano。

the　shape　of　a　dna　molecule；　as　everyone　knows；　is　rather　like　a　spiral　staircase　ortwisted　rope　ladder：　the　famous　double　helix。　the　uprights　of　this　structure　are　made　of　a　typeof　sugar　called　deoxyribose；　and　the　whole　of　the　helix　is　a　nucleic　acid—hence　the　name“deoxyribonucleic　acid。”　the　rungs　（or　steps）　are　formed　by　two　bases　joining　across　thespace　between；　and　they　can　bine　in　only　two　ways：　guanine　is　always　paired　withcytosine　and　thiamine　always　with　adenine。　the　order　in　which　these　letters　appear　as　youmove　up　or　down　the　ladder　constitutes　the　dna　code；　logging　it　has　been　the　job　of　thehuman　genome　project。

now　the　particular　brilliance　of　dna　lies　in　its　manner　of　replication。　when　it　is　time　toproduce　a　new　dna　molecule；　the　two　strands　part　down　the　middle；　like　the　zipper　on　ajacket；　and　each　half　goes　off　to　form　a　new　partnership。　because　each　nucleotide　along　astrand　pairs　up　with　a　specific　other　nucleotide；　each　strand　serves　as　a　template　for　thecreation　of　a　new　matching　strand。　if　you　possessed　just　one　strand　of　your　own　dna；　youcould　easily　enough　reconstruct　the　matching　side　by　working　out　the　necessary　partnerships：

if　the　topmost　rung　on　one　strand　was　made　of　guanine；　then　you　would　know　that　thetopmost　rung　on　the　matching　strand　must　be　cytosine。　work　your　way　down　the　ladderthrough　all　the　nucleotide　pairings；　and　eventually　you　would　have　the　code　for　a　newmolecule。　that　is　just　what　happens　in　nature；　except　that　nature　does　it　really　quickly—inonly　a　matter　of　seconds；　which　is　quite　a　feat。

most　of　the　time　our　dna　replicates　with　dutiful　accuracy；　but　just　occasionally—abo