A Short History of Nearly Everything- 第66部分

in　1969；　in　an　attempt　to　bring　some　order　to　the　growing　inadequacies　of　classification；　anecologist　from　cornell　university　named　r。　h。　whittaker　unveiled　in　the　journalscience　aproposal　to　divide　life　into　five　principal　branches—kingdoms；　as　they　are　known—calledanimalia；　plantae；　fungi；　protista；　and　monera。　protista；　was　a　modification　of　an　earlierterm；　protoctista；　which　had　been　suggested　a　century　earlier　by　a　scottish　biologist　namedjohn　hogg；　and　was　meant　to　describe　any　organisms　that　were　neither　plant　nor　animal。

though　whittaker’s　new　scheme　was　a　great　improvement；　protista　remained　ill　defined。

some　taxonomists　reserved　it　for　large　unicellular　organisms—the　eukaryotes—but　otherstreated　it　as　the　kind　of　odd　sock　drawer　of　biology；　putting　into　it　anything　that　didn’t　fitanywhere　else。　it　included　（depending　on　which　text　you　consulted）　slime　molds；　amoebas；and　even　seaweed；　among　much　else。　by　one　calculation　it　contained　as　many　as　200；000different　species　of　organism　all　told。　that’s　a　lot　of　odd　socks。

ironically；　just　as　whittaker’s　five…kingdom　classification　was　beginning　to　find　its　wayinto　textbooks；　a　retiring　academic　at　the　university　of　illinois　was　groping　his　way　toward　adiscovery　that　would　challenge　everything。　his　name　was　carl　woese　（rhymes　with　rose）；　andsince　the　mid…1960s—or　about　as　early　as　it　was　possible　to　do　so—he　had　been　quietlystudying　genetic　sequences　in　bacteria。　in　the　early　days；　this　was　an　exceedingly　painstakingprocess。　work　on　a　single　bacterium　could　easily　consume　a　year。　at　that　time；　according　towoese；　only　about　500　species　of　bacteria　were　known；　which　is　fewer　than　the　number　ofspecies　you　have　in　your　mouth。　today　the　number　is　about　ten　times　that；　though　that　is　stillfar　short　of　the　26；900　species　of　algae；　70；000　of　fungi；　and　30；800　of　amoebas　and　relatedorganisms　whose　biographies　fill　the　annals　of　biology。

it　isn’t　simple　indifference　that　keeps　the　total　low。　bacteria　can　be　exasperatingly　difficultto　isolate　and　study。　only　about　1　percent　will　grow　in　culture。　considering　how　wildlyadaptable　they　are　in　nature；　it　is　an　odd　fact　that　the　one　place　they　seem　not　to　wish　to　live　isa　petri　dish。　plop　them　on　a　bed　of　agar　and　pamper　them　as　you　will；　and　most　will　just　liethere；　declining　every　inducement　to　bloom。　any　bacterium　that　thrives　in　a　lab　is　bydefinition　exceptional；　and　yet　these　were；　almost　exclusively；　the　organisms　studied　bymicrobiologists。　it　was；　said　woese；　“like　learning　about　animals　from　visiting　zoos。”

genes；　however；　allowed　woese　to　approach　microorganisms　from　another　angle。　as　heworked；　woese　realized　that　there　were　more　fundamental　divisions　in　the　microbial　worldthan　anyone　suspected。　a　lot　of　little　organisms　that　looked　like　bacteria　and　behaved　likebacteria　were　actually　something　else　altogether—something　that　had　branched　off　frombacteria　a　long　time　ago。　woese　called　these　organisms　archaebacteria；　later　shortened　toarchaea。

it　has　be　said　that　the　attributes　that　distinguish　archaea　from　bacteria　are　not　the　sort　thatwould　quicken　the　pulse　of　any　but　a　biologist。　they　are　mostly　differences　in　their　lipids　andan　absence　of　something　called　peptidoglycan。　but　in　practice　they　make　a　world　ofdifference。　archaeans　are　more　different　from　bacteria　than　you　and　i　are　from　a　crab　orspider。　singlehandedly　woese　had　discovered　an　unsuspected　division　of　life；　so　fundamentalthat　it　stood　above　the　level　of　kingdom　at　the　apogee　of　the　universal　tree　of　life；　as　it　israther　reverentially　known。

in　1976；　he　startled　the　world—or　at　least　the　little　bit　of　it　that　was　paying　attention—byredrawing　the　tree　of　life　to　incorporate　not　five　main　divisions；　but　twenty…three。　these　hegrouped　under　three　new　principal　categories—bacteria；　archaea；　and　eukarya　（sometimesspelled　eucarya）—which　he　called　domains。

woese’s　new　divisions　did　not　take　the　biological　world　by　storm。　some　dismissed　them　asmuch　too　heavily　weighted　toward　the　microbial。　many　just　ignored　them。　woese；　accordingto　frances　ashcroft；　“felt　bitterly　disappointed。”　but　slowly　his　new　scheme　began　to　catchon　among　microbiologists。　botanists　and　zoologists　were　much　slower　to　admire　its　virtues。

it’s　not　hard　to　see　why。　on　woese’s　model；　the　worlds　of　botany　and　zoology　are　relegatedto　a　few　twigs　on　the　outermost　branch　of　the　eukaryan　limb。　everything　else　belongs　tounicellular　beings。

“these　folks　were　brought　up　to　classify　in　terms　of　gross　morphological　similarities　anddifferences；”　woese　told　an　interviewer　in　1996。　“the　idea　of　doing　so　in　terms　of　molecularsequence　is　a　bit　hard　for　many　of　them　to　swallow。”　in　short；　if　they　couldn’t　see　a　differencewith　their　own　eyes；　they　didn’t　like　it。　and　so　they　persisted　with　the　traditional　five…kingdom　division—an　arrangement　that　woese　called　“not　very　useful”　in　his　mildermoments　and　“positively　misleading”　much　of　the　rest　of　the　time。　“biology；　like　physicsbefore　it；”　woese　wrote；　“has　moved　to　a　level　where　the　objects　of　interest　and　theirinteractions　often　cannot　be　perceived　through　direct　observation。”

in　1998　the　great　and　ancient　harvard　zoologist　ernst　mayr　（who　then　was　in　his　ninety…fourth　year　and　at　the　time　of　my　writing　is　nearing　one　hundred　and　still　going　strong）　stirredthe　pot　further　by　declaring　that　there　should　be　just　two　prime　divisions　of　life—“empires”

he　called　them。　in　a　paper　published　in　the　proceedings　of　the　national　academy　of　sciences；mayr　said　that　woese’s　findings　were　interesting　but　ultimately　misguided；　noting　that“woese　was　not　trained　as　a　biologist　and　quite　naturally　does　not　have　an　extensivefamiliarity　with　the　principles　of　classification；”　which　is　perhaps　as　close　as　onedistinguished　scientist　can　e　to　saying　of　another　that　he　doesn’t　know　what　he　is　talkingabout。

the　specifics　of　mayr’s　criticisms　are　too　technical　to　need　extensive　airing　here—theyinvolve　issues　of　meiotic　sexuality；　hennigian　cladification；　and　controversial　interpretationsof　the　genome　of　methanobacterium　thermoautrophicum；　among　rather　a　lot　else—butessentially　he　argues　that　woese’s　arrangement　unbalances　the　tree　of　life。　the　bacterialrealm；　mayr　notes；　consists　of　no　more　than　a　few　thousand　species　while　the　archaean　has　amere　175　named　specimens；　with　perhaps　a　few　thousand　more　to　be　found—“but　hardlymore　than　that。”　by　contrast；　the　eukaryotic　realm—that　is；　the　plicated　organisms　withnucleated　cells；　like　us—numbers　already　in　the　millions。　for　the　sake　of　“the　principle　ofbalance；”　mayr　argues　for　bining　the　simple　bacterial　organisms　in　a　single　category；prokaryota；　while　placing　the　more　plex　and　“highly　evolved”　remainder　in　the　empireeukaryota；　which　would　stand　alongside　as　an　equal。　put　another　way；　he　argues　for　keepingthings　much　as　they　were　before。　this　division　between　simple　cells　and　plex　cells　“iswhere　the　great　break　is　in　the　living　world。”

the　distinction　between　halophilic　archaeans　and　methanosarcina　or　between　flavobacteriaand　gram…positive　bacteria　clearly　will　never　be　a　matter　of　moment　for　most　of　us；　but　it　isworth　remembering　that　each　is　as　different　from　its　neighbors　as　animals　are　from　plants。　ifwoese’s　new　arrangement　teaches　us　anything　it　is　that　life　really　is　various　and　that　most　ofthat　variety　is　small；　unicellular；　and　unfamiliar。　it　is　a　natural　human　impulse　to　think　ofevolution　as　a　long　chain　of　improvements；　of　a　never…ending　advance　toward　largeness　andplexity—in　a　word；　toward　us。　we　flatter　ourselves。　most　of　the　real　diversity　inevolution　has　been　small…scale。　we　large　things　are　just　flukes—an　interesting　side　branch。　ofthe　twenty…three　main　divisions　of　life；　only　three—plants；　animals；　and　fungi—are　largeenough　to　be　seen　by　the　human　eye；　and　even　they　contain　species　that　are　microscopic。

indeed；　according　to　woese；　if　you　totaled　up　all　the　biomass　of　the　planet—every　livingthing；　plants　included—microbes　would　account　for　at　least　80　percent　of　all　there　is；　perhapsmore。　the　world　belongs　to　the　very　small—and　it　has　for　a　very　long　time。

so　why；　you　are　bound　to　ask　at　some　point　in　your　life；　do　microbes　so　often　want　to　hurtus？　what　possible　satisfaction　could　there　be　to　a　microbe　in　having　us　grow　feverish　orchilled；　or　disfigured　with　sores；　or　above　all　expire？　a　dead　host；　after　all；　is　hardly　going　toprovide　long…term　hospitality。

to　begin　with；　it　is　worth　remembering　that　most　microorganisms　are　neutral　or　evenbeneficial　to　human　well…being。　the　most　rampantly　infectious　organism　on　earth；　abacterium　called　wolbachia；　doesn’t　hurt　humans　at　all—or；　e　to　that；　any　othervertebrates—but　if　you　are　a　shrimp　or　worm　or　fruit　fly；　it　can　make　you　wish　you　had　neverbeen　born。　altogether；　only　about　one　microbe　in　a　thousand　is　a　pathogen　for　humans；according　to　national　geographic　—though；　knowing　what　some　of　them　can　do；　we　couldbe　forgiven　for　thinking　that　that　is　quite　enough。　even　if　mostly　benign；　microbes　are　still　thenumber…three　killer　in　the　western　world；　and　even　many　less　lethal　ones　of　course　make　usdeeply　rue　their　existence。

making　a　host　unwell　has　certain　benefits　for　the　microbe。　the　sym