A Short History of Nearly Everything-第91章

按键盘上方向键 ← 或 → 可快速上下翻页，按键盘上的 Enter 键可回到本书目录页，按键盘上方向键 ↑ 可回到本页顶部！
————未阅读完？加入书签已便下次继续阅读！


xample—are　caused　by　lone　dysfunctional　genes；　but　as　a　rule　disruptivegenes　are　weeded　out　by　natural　selection　long　before　they　can　bee　permanentlytroublesome　to　a　species　or　population。　for　the　most　part　our　fate　and　fort—and　even　oureye　color—are　determined　not　by　individual　genes　but　by　plexes　of　genes　working　inalliance。　that’s　why　it　is　so　hard　to　work　out　how　it　all　fits　together　and　why　we　won’t　beproducing　designer　babies　anytime　soon。

in　fact；　the　more　we　have　learned　in　recent　years　the　more　plicated　matters　have　tendedto　bee。　even　thinking；　it　turns　out；　affects　the　ways　genes　work。　how　fast　a　man’s　beardgrows；　for　instance；　is　partly　a　function　of　how　much　he　thinks　about　sex　（because　thinkingabout　sex　produces　a　testosterone　surge）。　in　the　early　1990s；　scientists　made　an　even　moreprofound　discovery　when　they　found　they　could　knock　out　supposedly　vital　genes　fromembryonic　mice；　and　the　mice　were　not　only　often　born　healthy；　but　sometimes　were　actuallyfitter　than　their　brothers　and　sisters　who　had　not　been　tampered　with。　when　certain　importantgenes　were　destroyed；　it　turned　out；　others　were　stepping　in　to　fill　the　breach。　this　wasexcellent　news　for　us　as　organisms；　but　not　so　good　for　our　understanding　of　how　cells　worksince　it　introduced　an　extra　layer　of　plexity　to　something　that　we　had　barely　begun　tounderstand　anyway。

it　is　largely　because　of　these　plicating　factors　that　cracking　the　human　genome　becameseen　almost　at　once　as　only　a　beginning。　the　genome；　as　eric　lander　of　mit　has　put　it；　is　likea　parts　list　for　the　human　body：　it　tells　us　what　we　are　made　of；　but　says　nothing　about　howwe　work。　what’s　needed　now　is　the　operating　manual—instructions　for　how　to　make　it　go。

we　are　not　close　to　that　point　yet。

so　now　the　quest　is　to　crack　the　human　proteome—a　concept　so　novel　that　the　termproteome　didn’t　even　exist　a　decade　ago。　the　proteome　is　the　library　of　information　thatcreates　proteins。　“unfortunately；”　observed　scientific　american　in　the　spring　of　2002；　“theproteome　is　much　more　plicated　than　the　genome。”

that’s　putting　it　mildly。　proteins；　you　will　remember；　are　the　workhorses　of　all　livingsystems；　as　many　as　a　hundred　million　of　them　may　be　busy　in　any　cell　at　any　moment。　that’sa　lot　of　activity　to　try　to　figure　out。　worse；　proteins’　behavior　and　functions　are　based　notsimply　on　their　chemistry；　as　with　genes；　but　also　on　their　shapes。　to　function；　a　protein　mustnot　only　have　the　necessary　chemical　ponents；　properly　assembled；　but　then　must　also　befolded　into　an　extremely　specific　shape。　“folding”　is　the　term　that’s　used；　but　it’s　amisleading　one　as　it　suggests　a　geometrical　tidiness　that　doesn’t　in　fact　apply。　proteins　loopand　coil　and　crinkle　into　shapes　that　are　at　once　extravagant　and　plex。　they　are　more　likefuriously　mangled　coat　hangers　than　folded　towels。

moreover；　proteins　are　（if　i　may　be　permitted　to　use　a　handy　archaism）　the　swingers　of　thebiological　world。　depending　on　mood　and　metabolic　circumstance；　they　will　allowthemselves　to　be　phosphorylated；　glycosylated；　acetylated；　ubiquitinated；　farneysylated；sulfated；　and　linked　to　glycophosphatidylinositol　anchors；　among　rather　a　lot　else。　often　ittakes　relatively　little　to　get　them　going；　it　appears。　drink　a　glass　of　wine；　as　scientificamerican　notes；　and　you　materially　alter　the　number　and　types　of　proteins　at　large　in　yoursystem。　this　is　a　pleasant　feature　for　drinkers；　but　not　nearly　so　helpful　for　geneticists　who　aretrying　to　understand　what　is　going　on。

it　can　all　begin　to　seem　impossibly　plicated；　and　in　some　ways　itis　impossiblyplicated。　but　there　is　an　underlying　simplicity　in　all　this；　too；　owing　to　an　equallyelemental　underlying　unity　in　the　way　life　works。　all　the　tiny；　deft　chemical　processes　thatanimate　cells—the　cooperative　efforts　of　nucleotides；　the　transcription　of　dna　into　rna—evolved　just　once　and　have　stayed　pretty　well　fixed　ever　since　across　the　whole　of　nature。　asthe　late　french　geneticist　jacques　monod　put　it；　only　half　in　jest：　“anything　that　is　true　of　e。

coli　must　be　true　of　elephants；　except　more　so。”

every　living　thing　is　an　elaboration　on　a　single　original　plan。　as　humans　we　are　mereincrements—each　of　us　a　musty　archive　of　adjustments；　adaptations；　modifications；　andprovidential　tinkerings　stretching　back　3。8　billion　years。　remarkably；　we　are　even　quiteclosely　related　to　fruit　and　vegetables。　about　half　the　chemical　functions　that　take　place　in　abanana　are　fundamentally　the　same　as　the　chemical　functions　that　take　place　in　you。

it　cannot　be　said　too　often：　all　life　is　one。　that　is；　and　i　suspect　will　forever　prove　to　be；　themost　profound　true　statement　there　is。

part　　vithe　road　to　usdescended　from　the　apes！　my　dear；let　us　hope　that　it　is　not　true；　but　if　it　is；let　us　pray　that　it　will　not　beegenerally　known。

…remark　attributed　to　the　wife　ofthe　bishop　of　worcester　afterdarwin’s　theory　of　evolution　was　explained　to　her

。d　xs　



27ICE　TIME

…小……说。网
i　had　a　dream；　which　was　notall　a　dream。

the　bright　sun　wasextinguish’d；　and　the　starsdid　wander　。　。　。

—byron；　“darkness”

in　1815　on　the　island　of　sumbawa　in　indonesia；　a　handsome　and　long…quiescent　mountainnamed　tambora　exploded　spectacularly；　killing　a　hundred　thousand　people　with　its　blast　andassociated　tsunamis。　it　was　the　biggest　volcanic　explosion　in　ten　thousand　years—150　timesthe　size　of　mount　st。　helens；　equivalent　to　sixty　thousand　hiroshima…sized　atom　bombs。

news　didn’t　travel　terribly　fast　in　those　days。　in　london；　the　times　ran　a　small　story—actually　a　letter　from　a　merchant—seven　months　after　the　event。　but　by　this　time　tambora’seffects　were　already　being　felt。　thirty…six　cubic　miles　of　smoky　ash；　dust；　and　grit　haddiffused　through　the　atmosphere；　obscuring　the　sun’s　rays　and　causing　the　earth　to　cool。

sunsets　were　unusually　but　blearily　colorful；　an　effect　memorably　captured　by　the　artist　j。　m。

w。　turner；　who　could　not　have　been　happier；　but　mostly　the　world　existed　under　anoppressive；　dusky　pall。　it　was　this　deathly　dimness　that　inspired　the　byron　lines　above。

spring　never　came　and　summer　never　warmed：　1816　became　known　as　the　year　withoutsummer。　crops　everywhere　failed　to　grow。　in　ireland　a　famine　and　associated　typhoidepidemic　killed　sixty…five　thousand　people。　in　new　england；　the　year　became　popularlyknown　as　eighteen　hundred　and　froze　to　death。　morning　frosts　continued　until　june　andalmost　no　planted　seed　would　grow。　short　of　fodder；　livestock　died　or　had　to　be　prematurelyslaughtered。　in　every　way　it　was　a　dreadful　year—almost　certainly　the　worst　for　farmers　inmodern　times。　yet　globally　the　temperature　fell　by　only　about　1。5　degrees　fahrenheit。　earth’snatural　thermostat；　as　scientists　would　learn；　is　an　exceedingly　delicate　instrument。

the　nineteenth　century　was　already　a　chilly　time。　for　two　hundred　years　europe　and　northamerica　in　particular　had　experienced　a　little　ice　age；　as　it　has　bee　known；　whichpermitted　all　kinds　of　wintry　events—frost　fairs　on　the　thames；　ice…skating　races　along　dutchcanals—that　are　mostly　impossible　now。　it　was　a　period；　in　other　words；　when　frigidity　wasmuch　on　people’s　minds。　so　we　may　perhaps　excuse　nineteenth…century　geologists　for　beingslow　to　realize　that　the　world　they　lived　in　was　in　fact　balmy　pared　with　former　epochs；and　that　much　of　the　land　around　them　had　been　shaped　by　crushing　glaciers　and　cold　thatwould　wreck　even　a　frost　fair。

they　knew　there　was　something　odd　about　the　past。　the　european　landscape　was　litteredwith　inexplicable　anomalies—the　bones　of　arctic　reindeer　in　the　warm　south　of　france；　hugerocks　stranded　in　improbable　places—and　they　often　came　up　with　inventive　but　not　terriblyplausible　explanations。　one　french　naturalist　named　de　luc；　trying　to　explain　how　graniteboulders　had　e　to　rest　high　up　on　the　limestone　flanks　of　the　jura　mountains；　suggestedthat　perhaps　they　had　been　shot　there　by　pressed　air　in　caverns；　like　corks　out　of　apopgun。　the　term　for　a　displaced　boulder　is　an　erratic；　but　in　the　nineteenth　century　theexpression　seemed　to　apply　more　often　to　the　theories　than　to　the　rocks。

the　great　british　geologist　arthur　hallam　has　suggested　that　if　james　hutton；　the　father　ofgeology；　had　visited　switzerland；　he　would　have　seen　at　once　the　significance　of　the　carvedvalleys；　the　polished　striations；　the　telltale　strand　lines　where　rocks　had　been　dumped；　and　theother　abundant　clues　that　point　to　passing　ice　sheets。　unfortunately；　hutton　was　not　a　traveler。

but　even　with　nothing　better　at　his　disposal　than　secondhand　accounts；　hutton　rejected　out　ofhand　the　idea　that　huge　boulders　had　been　carried　three　thousand　feet　up　mountainsides　byfloods—all　the　water　in　the　world　won’t　make　a　boulder　float；　he　pointed　out—and　becameone　of　the　first　to　argue　for　widespread　glaciation。　unfortunately　his　ideas　escaped　notice；　andfor　another　half　century　most　naturalists　continued　to　insist　that　the　gouges　on　rocks　could　beattributed　to　passing　carts　or　even　the　scrape　of　hobnailed　boots。

local　　peasants；　　uncontaminated　　by　　scientific　orthodoxy；　knew　better；　however。　thenaturalist　jean　de　charpentier　told　the　story　of　how　in　1834　he　was　walking　along　a　countrylane　with　a　swiss　woodcutter　wh