万物简史英文版_比尔·布莱森-第58章

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　while　still　buried。　in　2001；　a　team　from　tel　aviv　university　argued　thatb。　permians　were　almost　identical　to　a　strain　of　modern　bacteria；　bacillus　marismortui；　foundin　the　dead　sea。　only　two　of　its　genetic　sequences　differed；　and　then　only　slightly。

鈥渁re　we　to　believe；鈥潯�the　israeli　researchers　wrote；　鈥渢hat　in　250　million　years　b。　permianshas　accumulated　the　same　amount　of　genetic　differences　that　could　be　achieved　in　just　3鈥�7days　in　the　laboratory？鈥潯�in　reply；　vreeland　suggested　that　鈥渂acteria　evolve　faster　in　the　labthan　they　do　in　the　wild。鈥�

maybe。

it　is　a　remarkable　fact　that　well　into　the　space　age；　most　school　textbooks　divided　the　worldof　the　living　into　just　two　categories鈥攑lant　and　animal。　microorganisms　hardly　featured。

amoebas　and　similar　single…celled　organisms　were　treated　as　proto…animals　and　algae　asproto…plants。　bacteria　were　usually　lumped　in　with　plants；　too；　even　though　everyone　knewthey　didn鈥檛　belong　there。　as　far　back　as　the　late　nineteenth　century　the　german　naturalisternst　haeckel　had　suggested　that　bacteria　deserved　to　be　placed　in　a　separate　kingdom；　whichhe　called　monera；　but　the　idea　didn鈥檛　begin　to　catch　on　among　biologists　until　the　1960s　andthen　only　among　some　of　them。　（i　note　that　my　trusty　american　heritage　desk　dictionaryfrom　1969　doesn鈥檛　recognize　the　term。）many　organisms　in　the　visible　world　were　also　poorly　served　by　the　traditional　division。

fungi；　the　group　that　includes　mushrooms；　molds；　mildews；　yeasts；　and　puffballs；　were　nearlyalways　treated　as　botanical　objects；　though　in　fact　almost　nothing　about　them鈥攈ow　theyreproduce　and　respire；　how　they　build　themselves鈥攎atches　anything　in　the　plant　world。

structurally　they　have　more　in　mon　with　animals　in　that　they　build　their　cells　from　chitin；a　material　that　gives　them　their　distinctive　texture。　the　same　substance　is　used　to　make　theshells　of　insects　and　the　claws　of　mammals；　though　it　isn鈥檛　nearly　so　tasty　in　a　stag　beetle　as　ina　portobello　mushroom。　above　all；　unlike　all　plants；　fungi　don鈥檛　photosynthesize；　so　theyhave　no　chlorophyll　and　thus　are　not　green。　instead　they　grow　directly　on　their　food　source；which　can　be　almost　anything。　fungi　will　eat　the　sulfur　off　a　concrete　wall　or　the　decayingmatter　between　your　toes鈥攖wo　things　no　plant　will　do。　almost　the　only　plantlike　quality　theyhave　is　that　they　root。

even　less　fortably　susceptible　to　categorization　was　the　peculiar　group　of　organismsformally　called　myxomycetes　but　more　monly　known　as　slime　molds。　the　name　no　doubthas　much　to　do　with　their　obscurity。　an　appellation　that　sounded　a　little　more　dynamic鈥斺�渁mbulant　self…activating　protoplasm；鈥潯�say鈥攁nd　less　like　the　stuff　you　find　when　you　reachdeep　into　a　clogged　drain　would　almost　certainly　have　earned　these　extraordinary　entities　amore　immediate　share　of　the　attention　they　deserve；　for　slime　molds　are；　make　no　mistake；among　the　most　interesting　organisms　in　nature。　when　times　are　good；　they　exist　as　one…celled　individuals；　much　like　amoebas。　but　when　conditions　grow　tough；　they　crawl　to　acentral　gathering　place　and　bee；　almost　miraculously；　a　slug。　the　slug　is　not　a　thing　ofbeauty　and　it　doesn鈥檛　go　terribly　far鈥攗sually　just　from　the　bottom　of　a　pile　of　leaf　litter　to　thetop；　where　it　is　in　a　slightly　more　exposed　position鈥攂ut　for　millions　of　years　this　may　wellhave　been　the　niftiest　trick　in　the　universe。

and　it　doesn鈥檛　stop　there。　having　hauled　itself　up　to　a　more　favorable　locale；　the　slimemold　transforms　itself　yet　again；　taking　on　the　form　of　a　plant。　by　some　curious　orderlyprocess　the　cells　reconfigure；　like　the　members　of　a　tiny　marching　band；　to　make　a　stalk　atopof　which　forms　a　bulb　known　as　a　fruiting　body。　inside　the　fruiting　body　are　millions　ofspores　that；　at　the　appropriate　moment；　are　released　to　the　wind　to　blow　away　and　beesingle…celled　organisms　that　can　start　the　process　again。

for　years　slime　molds　were　claimed　as　protozoa　by　zoologists　and　as　fungi　by　mycologists；though　most　people　could　see　they　didn鈥檛　really　belong　anywhere。　when　genetic　testingarrived；　people　in　lab　coats　were　surprised　to　find　that　slime　molds　were　so　distinctive　andpeculiar　that　they　weren鈥檛　directly　related　to　anything　else　in　nature；　and　sometimes　not　evento　each　other。

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鈥攌ingdoms；　as　they　are　known鈥攃alledanimalia；　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鈥檚　new　scheme　was　a　great　improvement；　protista　remained　ill　defined。

some　taxonomists　reserved　it　for　large　unicellular　organisms鈥攖he　eukaryotes鈥攂ut　otherstreated　it　as　the　kind　of　odd　sock　drawer　of　biology；　putting　into　it　anything　that　didn鈥檛　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鈥檚　a　lot　of　odd　socks。

ironically；　just　as　whittaker鈥檚　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鈥攐r　about　as　early　as　it　was　possible　to　do　so鈥攈e　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鈥檛　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；　鈥渓ike　learning　about　animals　from　visiting　zoos。鈥�

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鈥攕omething　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鈥攐r　at　least　the　little　bit　of　it　that　was　paying　attention鈥攂yredrawing　the　tree　of　life　to　incorporate　not　five　main　divisions；　but　twenty…three。　these　hegrouped　under　three　new　principal　categories鈥攂acteria；　archaea；　and　eukarya　（sometimesspelled　eucarya）鈥攚hich　he　called　domains。

woese鈥檚　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；　鈥渇elt　bitterly　disappointed。鈥潯�but　slowly　his　new　scheme　began　to　catchon　among　microbiologists。　botanists　and　zoologists　were　much　slower　to　admire　its　virtues。

it鈥檚　not　hard　to　see　why。　on　woese鈥檚　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。

鈥渢hese　folks　were　brought　up　to　classify　in　terms　of　gross　morphological　similarities　anddifferences；鈥潯�woese　told　an　interviewer　in　1996。　鈥渢he　idea　of　doing　so　in　terms　of　molecularsequence　is　a　bit　hard　for　many　of　them　to　swallow。鈥潯�in　short；　if　they　couldn鈥檛　see　a　differencewith　their　own　eyes；　they　didn鈥檛　like　it。　and　so　they　persisted　with　the　traditional　five…kingdom　division鈥攁n　arrangement　that　woese　called　鈥渘ot　very　useful鈥潯�in　his　mildermoments　and　鈥減ositively　misleading鈥潯�much　of　the　rest　of　the　time。　鈥渂iology；　like　physicsbefore　it；鈥潯�woese　wrote；　鈥渉as　moved　to　a　level　where　the　objects　of　interest　and　theirinteractions　often　cannot　be　perceived　through　direct　observation。鈥�

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鈥斺�渆mpires鈥�

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

the　specifics　of　mayr鈥檚　criticisms　are　too　technical　to　need　extensive　airing　here鈥攖heyinvolve　issues　of　meiotic　sexuality；　hennigian　cladification；　and　controversial　interpretationsof　the　genome　of　methanobacterium　thermoautrophicum；　among　rather　a　lot　else鈥攂utessentially　he　argues　that　woese鈥檚　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鈥斺�渂ut　hardlymore　than　that。鈥潯�by　contrast；　the　eukaryotic　realm鈥攖hat　is；　the　plicated　organisms　withnucleated　cells；　like　us鈥攏umbers　already　in　the　millions。　for　the　sake　of　鈥渢he　principle　ofbalance；鈥潯�mayr　argues　for　bining　the　simple　bacterial　organisms　in　a　single　category；prokaryota；　while　placing　the　more　plex　and　鈥渉ighly　evolved鈥潯�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　鈥渋swhere