万物简史英文版_比尔·布莱森-第72章

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ry　second　from　every　direction。　even　for　its　full…time　occupants　theinside　of　a　cell　is　a　hazardous　place。　each　strand　of　dna　is　on　average　attacked　or　damagedonce　every　8。4　seconds鈥攖en　thousand　times　in　a　day鈥攂y　chemicals　and　other　agents　thatwhack　into　or　carelessly　slice　through　it；　and　each　of　these　wounds　must　be　swiftly　stitched　upif　the　cell　is　not　to　perish。

the　proteins　are　especially　lively；　spinning；　pulsating；　and　flying　into　each　other　up　to　abillion　times　a　second。　enzymes；　themselves　a　type　of　protein；　dash　everywhere；　performingup　to　a　thousand　tasks　a　second。　like　greatly　speeded　up　worker　ants；　they　busily　build　andrebuild　molecules；　hauling　a　piece　off　this　one；　adding　a　piece　to　that　one。　some　monitorpassing　proteins　and　mark　with　a　chemical　those　that　are　irreparably　damaged　or　flawed。　onceso　selected；　the　doomed　proteins　proceed　to　a　structure　called　a　proteasome；　where　they　arestripped　down　and　their　ponents　used　to　build　new　proteins。　some　types　of　protein　existfor　less　than　half　an　hour；　others　survive　for　weeks。　but　all　lead　existences　that　areinconceivably　frenzied。　as　de　duve　notes；　鈥渢he　molecular　world　must　necessarily　remainentirely　beyond　the　powers　of　our　imagination　owing　to　the　incredible　speed　with　whichthings　happen　in　it。鈥�

but　slow　things　down；　to　a　speed　at　which　the　interactions　can　be　observed；　and　thingsdon鈥檛　seem　quite　so　unnerving。　you　can　see　that　a　cell　is　just　millions　of　objects鈥攍ysosomes；endosomes；　ribosomes；　ligands；　peroxisomes；　proteins　of　every　size　and　shape鈥攂umping　intomillions　of　other　objects　and　performing　mundane　tasks：　extracting　energy　from　nutrients；assembling　structures；　getting　rid　of　waste；　warding　off　intruders；　sending　and　receivingmessages；　making　repairs。　typically　a　cell　will　contain　some　20；000　different　types　of　protein；and　of　these　about　2；000　types　will　each　be　represented　by　at　least　50；000　molecules。　鈥渢hismeans；鈥潯�says　nuland；　鈥渢hat　even　if　we　count　only　those　molecules　present　in　amounts　of　morethan　50；000　each；　the　total　is　still　a　very　minimum　of　100　million　protein　molecules　in　eachcell。　such　a　staggering　figure　gives　some　idea　of　the　swarming　immensity　of　biochemicalactivity　within　us。鈥�

it　is　all　an　immensely　demanding　process。　your　heart　must　pump　75　gallons　of　blood　anhour；　1；800　gallons　every　day；　657；000　gallons　in　a　year鈥攖hat鈥檚　enough　to　fill　four　olympic…sized　swimming　pools鈥攖o　keep　all　those　cells　freshly　oxygenated。　（and　that鈥檚　at　rest。　duringexercise　the　rate　can　increase　as　much　as　sixfold。）　the　oxygen　is　taken　up　by　themitochondria。　these　are　the　cells鈥櫋�power　stations；　and　there　are　about　a　thousand　of　them　in　atypical　cell；　though　the　number　varies　considerably　depending　on　what　a　cell　does　and　howmuch　energy　it　requires。

you　may　recall　from　an　earlier　chapter　that　the　mitochondria　are　thought　to　have　originatedas　captive　bacteria　and　that　they　now　live　essentially　as　lodgers　in　our　cells；　preserving　theirown　genetic　instructions；　dividing　to　their　own　timetable；　speaking　their　own　language。　youmay　also　recall　that　we　are　at　the　mercy　of　their　goodwill。　here鈥檚　why。　virtually　all　the　foodand　oxygen　you　take　into　your　body　are　delivered；　after　processing；　to　the　mitochondria；where　they　are　converted　into　a　molecule　called　adenosine　triphosphate；　or　atp。

you　may　not　have　heard　of　atp；　but　it　is　what　keeps　you　going。　atp　molecules　areessentially　little　battery　packs　that　move　through　the　cell　providing　energy　for　all　the　cell鈥檚processes；　and　you　get　through　a　lot　of　it。　at　any　given　moment；　a　typical　cell　in　your　bodywill　have　about　one　billion　atp　molecules　in　it；　and　in　two　minutes　every　one　of　them　willhave　been　drained　dry　and　another　billion　will　have　taken　their　place。　every　day　you　produceand　use　up　a　volume　of　atp　equivalent　to　about　half　your　body　weight。　feel　the　warmth　ofyour　skin。　that鈥檚　your　atp　at　work。

when　cells　are　no　longer　needed；　they　die　with　what　can　only　be　called　great　dignity。　theytake　down　all　the　struts　and　buttresses　that　hold　them　together　and　quietly　devour　theirponent　parts。　the　process　is　known　as　apoptosis　or　programmed　cell　death。　every　daybillions　of　your　cells　die　for　your　benefit　and　billions　of　others　clean　up　the　mess。　cells　canalso　die　violently鈥攆or　instance；　when　infected鈥攂ut　mostly　they　die　because　they　are　told　to。

indeed；　if　not　told　to　live鈥攊f　not　given　some　kind　of　active　instruction　from　another　cell鈥攃ells　automatically　kill　themselves。　cells　need　a　lot　of　reassurance。

when；　as　occasionally　happens；　a　cell　fails　to　expire　in　the　prescribed　manner；　but　ratherbegins　to　divide　and　proliferate　wildly；　we　call　the　result　cancer。　cancer　cells　are　really　justconfused　cells。　cells　make　this　mistake　fairly　regularly；　but　the　body　has　elaboratemechanisms　for　dealing　with　it。　it　is　only　very　rarely　that　the　process　spirals　out　of　control。　onaverage；　humans　suffer　one　fatal　malignancy　for　each　100　million　billion　cell　divisions。

cancer　is　bad　luck　in　every　possible　sense　of　the　term。

the　wonder　of　cells　is　not　that　things　occasionally　go　wrong；　but　that　they　manageeverything　so　smoothly　for　decades　at　a　stretch。　they　do　so　by　constantly　sending　andmonitoring　streams　of　messages鈥攁　cacophony　of　messages鈥攆rom　all　around　the　body：

instructions；　queries；　corrections；　requests　for　assistance；　updates；　notices　to　divide　or　expire。

most　of　these　signals　arrive　by　means　of　couriers　called　hormones；　chemical　entities　such　asinsulin；　adrenaline；　estrogen；　and　testosterone　that　convey　information　from　remote　outpostslike　the　thyroid　and　endocrine　glands。　still　other　messages　arrive　by　telegraph　from　the　brainor　from　regional　centers　in　a　process　called　paracrine　signaling。　finally；　cells　municatedirectly　with　their　neighbors　to　make　sure　their　actions　are　coordinated。

what　is　perhaps　most　remarkable　is　that　it　is　all　just　random　frantic　action；　a　sequence　ofendless　encounters　directed　by　nothing　more　than　elemental　rules　of　attraction　and　repulsion。

there　is　clearly　no　thinking　presence　behind　any　of　the　actions　of　the　cells。　it　all　just　happens；smoothly　and　repeatedly　and　so　reliably　that　seldom　are　we　even　conscious　of　it；　yet　somehowall　this　produces　not　just　order　within　the　cell　but　a　perfect　harmony　right　across　the　organism。

in　ways　that　we　have　barely　begun　to　understand；　trillions　upon　trillions　of　reflexive　chemicalreactions　add　up　to　a　mobile；　thinking；　decision…making　you鈥攐r；　e　to　that；　a　rather　lessreflective　but　still　incredibly　organized　dung　beetle。　every　living　thing；　never　forget；　is　awonder　of　atomic　engineering。

indeed；　some　organisms　that　we　think　of　as　primitive　enjoy　a　level　of　cellular　organizationthat　makes　our　own　look　carelessly　pedestrian。　disassemble　the　cells　of　a　sponge　（by　passingthem　through　a　sieve；　for　instance）；　then　dump　them　into　a　solution；　and　they　will　find　theirway　back　together　and　build　themselves　into　a　sponge　again。　you　can　do　this　to　them　overand　over；　and　they　will　doggedly　reassemble　because；　like　you　and　me　and　every　other　livingthing；　they　have　one　overwhelming　impulse：　to　continue　to　be。

and　that鈥檚　because　of　a　curious；　determined；　barely　understood　molecule　that　is　itself　notalive　and　for　the　most　part　doesn鈥檛　do　anything　at　all。　we　call　it　dna；　and　to　begin　tounderstand　its　supreme　importance　to　science　and　to　us　we　need　to　go　back　160　years　or　so　tovictorian　england　and　to　the　moment　when　the　naturalist　charles　darwin　had　what　has　beencalled　鈥渢he　single　best　idea　that　anyone　has　ever　had鈥濃�攁nd　then；　for　reasons　that　take　a　littleexplaining；　locked　it　away　in　a　drawer　for　the　next　fifteen　years。

w锛穡锛巟i锛�osh锛祇txt。c锛痬



25　　　　DARWIN鈥橲　SINGULAR　NOTION

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in　the　late　summer　or　early　autumn　of　1859；　whitwell　elwin；　editor　of　the　respectedbritish　journal　the　quarterly　review；　was　sent　an　advance　copy　of　a　new　book　by　thenaturalist　charles　darwin。　elwin　read　the　book　with　interest　and　agreed　that　it　had　merit；　butfeared　that　the　subject　matter　was　too　narrow　to　attract　a　wide　audience。　he　urged　darwin　towrite　a　book　about　pigeons　instead。　鈥渆veryone　is　interested　in　pigeons；鈥潯�he　observedhelpfully。

elwin鈥檚　sage　advice　was　ignored；　and　on　the　origin　of　species　by　means　of　naturalselection；　or　the　preservation　of　favoured　races　in　the　struggle　for　life　was　published　in　latenovember　1859；　priced　at　fifteen　shillings。　the　first　edition　of　1；250　copies　sold　out　on　thefirst　day。　it　has　never　been　out　of　print；　and　scarcely　out　of　controversy；　in　all　the　time　since鈥攏ot　bad　going　for　a　man　whose　principal　other　interest　was　earthworms　and　who；　but　for　asingle　impetuous　decision　to　sail　around　the　world；　would　very　probably　have　passed　his　lifeas　an　anonymous　country　parson　known　for；　well；　for　an　interest　in　earthworms。

charles　robert　darwin　was　born　on　february　12；　1809；1in　shrewsbury；　a　sedate　markettown　in　the　west　midlands　of　england。　his　father　was　a　prosperous　and　well…regardedphysician。　his　mother；　who　died　when　charles　was　only　eight；　was　the　daughter　of　josiahwedgwood；　of　pottery　fame。

darwin　enjoyed　every　advantage　of　upbringing；　but　continually　pained　his　widowed　fatherwith　his　lackluster　academic　performance。　鈥測ou　care　for　nothing　but　shooting；　dogs；　and　rat…catching；　and　you　will　be　a　disgrace　to　yourself　and　all　your　family；鈥潯�his　father　wrote　in　a　linethat　nearly　always　appears　just　about　here　in　any　review　of　darwin鈥檚　early　life。　although　hisinclination　was　to　natural　history；　for　his　father鈥檚　sake　he　tried　to　study　medicine　at　edinburghuniversity　but　couldn鈥檛　bear　the　blood　and　suffering。　the　experience　of　witnessing　anoperation　on　an　understandably　distressed　child鈥攖his　was　in　the　days　before　anesthetics；　ofcourse鈥攍eft　him　permanently　traumatized。　he　tried　law　instead；　but　found　that　insupportablydull　and　finally　managed；　more　or　less　by　default；　to　acquire　a　degree　in　divinity　fromcambridge。

a　life　in　a　rural　vicarage　seemed　to　await　him　when　from　out　of　the　blue　there　came　a　moretempting　offer。　darwin　was　invited　to　sail　on　the　naval　survey　ship　hms　beagle；　essentiallyas　dinner　pany　for　the　captain；　robert　fitzroy；　whose　rank　precluded　his　socializing　withanyone　other　than　a　gentleman。　fitzroy；　who　was　very　odd；　chose　darwin　in　part　because　heliked　the　shape　of　darwin鈥檚　nose。　（it　betokened　depth　of　character；　he　believed。）　darwin　wasnot　fitzroy鈥檚　first　choice；　but　got　the　nod　when　fitzroy鈥檚　preferred　panion　dropped　out。

from　a　twenty…first…century　perspective　the　two　men鈥檚　most　striking　joint　feature　was　their1an　auspicious　date　in　history：　on　the　same　day　in　kentucky；　abraham　lincoln　was　born。

extreme　youthfulness。　at　the　time　of　sailing；　fitzroy　was　only　twenty…three；　darwin　justtwenty…two。

fitzroy鈥檚　formal　assignment　was　to　chart　coastal　waters；　but　his　hobby鈥攑assion　really鈥攚as　to　seek　out　evidence　for　a　literal；　biblical　interpretation　of　creation。　that　darwin　wastrained　for　the　ministry　was　central　to　fitzroy鈥檚　decision　to　have　him　aboard。　that　darwinsubsequently　proved　to　be　not　only　liberal　of　view　but　less　than　wholeheartedly　devoted　tochristian　fundamentals　became　a　source　of　lasting　friction　between　them。

darwin鈥檚　time　aboard　hms　beagle；　from　1831　to　1836；　was　obviou