the.lost.world-第35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！


tually　the　extinct　predecessors　of　living　animals。　The　implications　of　Darwin's　idea　upset　lots　of　people。　They　didn't　like　to　think　of　God's　creations　changing；　and　they　didn't　like　to　think　of　monkeys　in　their　family　trees。　It　was　embarrassing　and　offensive。　The　debate　was　fierce。　But　Darwin　amassed　a　tremendous　amount　of　factual　data　…　he　had　made　an　overwhelming　case。　So　gradually　his　idea　of　evolution　was　accepted　by　scientists；　and　by　the　world　at　large。　But　the　question　remained：　how　does　evolution　happen？　For　that；　Darwin　didn't　have　a　good　answer。〃
　　　　〃　Natural　selection；〃　Arby　said。
　　　　〃Yes；　that　was　Darwin's　explanation。　The　environment　exerts　pressure　which　favors　certain　animals；　and　they　breed　more　often　in　subsequent　generations；　and　that's　how　evolution　occurs。　But　as　many　people　realized；　natural　selection　isn't　really　an　explanation。　It's　just　a　definition：　if　an　animal　succeeds；　it　must　have　been　selected　for。　But　what　in　the　animal　is　favored？　And　how　does　natural　selection　actually　operate？　Darwin　had　no　idea。　And　neither　did　anybody　else　for　another　fifty　years。〃
　　　　〃But　it's　genes；〃　Kelly　said。
　　　　〃Okay；〃　Malcolm　said。　〃Fine。　We　e　to　the　twentieth　century。　Mendel's　work　with　plants　is　rediscovered。　Fischer　and　Wright　do　population　studies。　Pretty　soon　we　know　genes　control　heredity…whatever　genes　are。　Remember；　through　the　first　half　of　the　century；　all　during　World　War　I　and　World　War　II；　nobody　had　any　idea　what　a　gene　was。　After　Watson　and　Crick　in　1953；　we　knew　that　genes　were　nucleotides　arranged　in　a　double　helix。　Great。　And　we　knew　about　mutation。　So　by　the　late　twentieth　century；　we　have　a　theory　of　natural　selection　which　says　that　mutations　arise　spontaneously　in　genes；　that　the　environment　favors　the　mutations　that　are　beneficial；　and　out　of　this　selection　process　evolution　occurs。　It's　simple　and　straightforward。　God　is　not　at　work。　No　higher　organizing　principle　involved。　In　the　end；　evolution　is　just　the　result　of　a　bunch　of　mutations　that　either　Survive　or　die。　Right？〃
　　　　〃Right；〃　Arby　said。
　　　　〃But　there　are　problems　with　that　idea；〃　Malcolm　said。　〃First　of　all；　there's　a　time　problem。　A　single　bacterium　…　the　earliest　form　of　life　has　two　thousand　enzymes。　Scientists　have　estimated　how　long　it　would　take　to　randomly　assemble　those　enzymes　from　a　primordial　soup。　Estimates　run　from　forty　billion　years　to　one　hundred　billion　years。　But　the　earth　is　only　four　billion　years　old。　So；　chance　alone　seems　too　slow。　Particularly　since　we　know　bacteria　actually　appeared　only　four　hundred　million　years　after　the　earth　began。　Life　appeared　very　fast　…　which　is　why　some　scientists　have　decided　life　on　earth　must　be　of　extraterrestrial　origin。　Although　I　think　that's　just　evading　the　issue。〃
　　　　〃Okay。。。〃
　　　　〃Second；　there's　the　coordination　problem。　If　you　believe　the　current　theory；　then　all　the　wonderful　plexity　of　life　is　nothing　but　the　accumulation　of　chance　events　…　a　bunch　of　genetic　accidents　strung　together。　Yet　when　we　look　closely　at　animals；　it　appears　as　if　many　elements　must　have　evolved　simultaneously。　Take　bats；　which　have　echolocation…they　navigate　by　sound。　To　do　that；　many　things　must　evolve。　Bats　need　a　specialized　apparatus　to　make　sounds；　they　need　specialized　ears　to　hear　echoes；　they　need　specialized　brains　to　interpret　the　sounds；　and　they　need　specialized　bodies　to　dive　and　swoop　and　catch　insects。　If　all　these　things　don't　evolve　simultaneously；　there's　no　advantage。　And　to　imagine　all　these　things　happen　purely　by　chance　is　like　imagining　that　a　tornado　can　hit　a　junkyard　and　assemble　the　Parts　into　a　working　747　airplane。　It's　very　hard　to　believe。〃
　　　　〃Okay；〃　Thorne　said。　〃I　agree。〃
　　　　〃Next　problem。　Evolution　doesn't　always　act　like　a　blind　force　should。　Certain　environmental　niches　don't　get　filled。　Certain　plants　don't　get　eaten。　And　certain　animals　don't　evolve　much。　Sharks　haven't　changed　for　a　hundred　and　sixty　million　years。　Opossums　haven't　changed　since　dinosaurs　became　extinct；　sixty…five　million　years　ago。　The　environments　for　these　animals　have　changed　dramatically；　but　the　animals　have　remained　almost　the　same。　Not　exactly　the　same；　but　almost。　In　other　words；　it　appears　they　haven't　responded　to　their　environment。〃
　　　　〃Maybe　they're　still　well　adapted；〃　Arby　said。
　　　　〃Maybe。　Or　maybe　there's　something　else　going　on　that　we　don't　understand。〃
　　　　〃　Like　what？〃
　　　　〃Like　other　rules　that　influence　the　oute。〃
　　　　Thorne　said；　〃Are　you　saying　evolution　is　directed？〃
　　　　〃No；〃　Malcolm　said。　〃That's　Creationism　and　it's　wrong。　Just　plain　wrong。　But　I　am　saying　that　natural　selection　acting　on　genes　is　probably　not　the　whole　story。　It's　too　simple。　Other　forces　are　also　at　work。　The　hemoglobin　molecule　is　a　protein　that　is　folded　like　a　sandwich　around　a　central　iron　atom　that　binds　oxygen。　Hemoglobin　expands　and　contracts　when　it　takes　on　and　gives　up　oxygen…like　a　tiny　molecular　lung。　Now；　we　know　the　sequence　of　amino　acids　that　make　up　hemoglobin。　But　we　don't　know　how　to　fold　it。　Fortunately；　we　don't　need　to　know　that；　because　if　you　make　the　molecule；　it　folds　all　by　itself。　It　organizes　itself。　And　it　turns　out；　again　and　again；　that　living　things　seem　to　have　a　self…organizing　quality。　Proteins　fold。　Enzymes　interact。　Cells　arrange　themselves　to　form　organs　and　the　organs　arrange　themselves　to　form　a　coherent　individual。　Individuals　organize　themselves　to　make　a　population。　And　populations　organize　themselves　to　make　a　coherent　biosphere。　From　plexity　theory；　we're　starting　to　have　a　sense　of　how　this　self…organization　may　happen；　and　what　it　means。　And　it　implies　a　major　change　in　how　we　view　evolution。〃
　　　　〃But；〃　Arby　said；　〃in　the　end；　evolution　still　must　be　the　result　of　the　environment　acting　on　genes。〃
　　　　〃I　don't　think　it's　enough；　Arb；〃　Malcolm　said。　〃I　think　more　is　involved　…　I　think　there　has　to　be　more；　even　to　explain　how　our　own　species　arose。〃

〃About　three　million　years　ago；〃　Malcolm　said；　〃some　African　apes　that　had　been　living　in　trees　came　down　to　the　ground。　There　was　nothing　special　about　these　apes。　Their　brains　were　small　and　they　weren't　especially　smart。　They　didn't　have　claws　or　sharp　teeth　for　weapons。　They　weren't　particularly　strong；　or　fast。　They　were　certainly　no　match　for　a　leopard。　But　because　they　were　short；　they　started　standing　upright　on　their　hind　legs；　to　see　over　the　tall　African　grass。　That's　how　it　began。　just　some　ordinary　apes；　looking　out　over　the　grass。
　　　　〃As　time　went　on；　the　apes　stood　upright　more　and　more　of　the　time。　That　left　their　hands　free　to　do　things。　Like　all　apes；　they　were　tool…users。　Chimps；　for　example；　use　twigs　to　fish　for　termites。　That　sort　of　thing。　As　time　went　on；　our　ape　ancestors　developed　more　plex　tools。　That　stimulated　their　brains　to　grow　in　size　and　plexity。　It　began　a　spiral：　more　plex　tools　provoked　more　plex　brains　which　provoked　more　plex　tools。　And　our　brains　literally　exploded；　in　evolutionary　terms。　Our　brains　more　than　doubled　in　size　in　about　a　million　years。　And　that　caused　problems　for　us。〃
　　　　〃Like　what？〃
　　　　〃Like　getting　born；　for　one　thing。　Big　brains　can't　pass　through　the　birth　canal　…　which　means　that　both　mother　and　child　die　in　childbirth。　That's　no　good。　What's　the　evolutionary　response？　To　make　human　infants　born　very　early　in　development；　when　their　brains　are　still　small　enough　to　pass　through　the　pelvis。　It's　the　marsupial　solution　…　most　of　the　growth　occurs　outside　the　mother's　body。　A　human　child's　brain　doubles　during　the　first　year　of　life。　That's　a　good　solution　to　the　problem　of　birth；　but　it　creates　other　problems。　It　means　that　human　children　will　be　helpless　long　after　birth。　The　infants　of　many　mammals　can　walk　minutes　after　they're　born。　Others　walk　in　a　few　days；　or　weeks。　But　human　infants　can't　walk　for　a　full　year。　They　can't　feed　themselves　for　even　longer。　So　one　price　of　big　brains　was　that　our　ancestors　had　to　evolve　new；　stable　social　organizations　to　permit　long…term　child　care；　lasting　many　years；　These　big…brained；　totally　helpless　children　changed　society。　But　that's　not　the　most　important　consequence。〃
　　　　〃No？〃
　　　　〃No。　Being　born　in　an　immature　state　means　that　human　infants　have　unformed　brains。　They　don't　arrive　with　a　lot　of　built…in；　instinctive　behavior。　Instinctively；　a　newborn　infant　can　suck　and　grasp；　but　that's　about　all。　plex　human　behavior　is　not　instinctive　at　all。　So　human　societies　had　to　develop　education　to　train　the　brains　of　their　children。　To　teach　them　how　to　act。　Every　human　society　expends　tremendous　time　and　energy　teaching　its　children　the　right　way　to　behave。　You　look　at　a　simpler　society；　in　the　rain　forest　somewhere；　and　you　find　that　every　child　is　born　into　a　network　of　adults　responsible　for　helping　to　raise　the　child。　Not　only　parents；　but　aunts　and　uncles　and　grandparents　and　tribal　elders。　Some　teach　the　child　to　hunt　or　gather　food　or　weave；　some　teach　them　about　sex　or　war。　But　the　responsibilities　are　clearly　defined；　and　if　a　child　does　not　have；　say；　a　mother's　brother's　sister　to　do　a　specific　teaching　job；　the　people　get　together　and　appoint　a　substitute。　Because　raising　children　is；　in　a　sense；　the　reason　the　society　exists　in　the　first　place。　It's　the　most　important　thing　that　happens；　and　it's　the　culmination　of　all　the　tools　and　language　and　social　structure　that　has　evolved。　And　eventually；　a　few　million　years　later；　we　have　kids　using　puters。
　　　　〃Now；　if　this　picture　makes　sense；　where　does　natural　selection　act？　Does　it　act　on　the　body；　enlarging　the　brain？　Does　it　act　on　the　developmental　sequence；　pushing　the　kids　out　early？　Does　it　act　on　social　behavior；　provoking　cooperation　and　child…caring？　Or　does　it　act　everywhere　all　at　once　…　on　bodies；　on　development；　and　on　social　behavior？〃
　　　　〃Everywhere　at　once；〃　Arby　said。
　　　　〃I　think　so；〃　Malcolm　said。　〃But　there　may　also　be　parts　of　this　story　that　happen　automatically；　the　result　of　self…organization。　For　example；　infants　of　all　species　have　a　characteristic　appearance。　Big　eyes；　big　heads；　small　faces；　uncoordinated　movements。　That's　true　of　kids　and　puppies　and　baby　birds。　And　it　seems　to　provoke　adults　of　all　species　to　act　tenderly　toward　them。　In　a　sense；　you　might　say　infant　appearance　seems　to　self…organize　adult　behavior。　And　in　our　case；　a　good　thing；　too。〃
　　　　Thorne　said；　〃What　does　that　have　to　do　with　dinosaur　extinction？〃
　　　　〃Self…organizing　principles　can　act　for　better　or　worse。　Just　as　self…organization　can　coordinate　change；　it　can　also　lead　a　population　into　decline；　and　cause　it　to　lose　its　edge。　On　this　island；　my　hope　is　we'll　see　self…organizing　adaptations　in　the　behavior　of　real　dinosaurs　…　and　it'll　tell　us　why　they　became　extinct。　In　fact；　I'm　pretty　sure　we　already　know　why　the　dinosaurs　became　extinct。〃
　　　　The　radio　clicked。　〃Bravo；〃　Levine　said；　over　the　inter。　〃I　couldn't　have　put　it　better　myself。　But　perhaps　you　better　see　what　is　happening　out　here。　The　parasaurs　are　doing　something　very　interesting；　Ian。〃
　　　　〃What's　that？〃
　　　　〃e　and　look。〃
　　　　〃Kids；〃　Malcolm　said；　〃you　stay　here　and　watch　the　monitors。〃　He　pressed　the　radio　button。　〃Richard？　We're　on　our　way。〃

Parasaurs

Richard　Levine　gripped　the　railing　of　the　high　hide；　and　watched　tensely。　Direct