万物简史英文版_比尔·布莱森-第85章

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all　the　elements　would　appear　to　have　been　in　place　for　the　rapid　evolution　of　a　potentbrain；　and　yet　that　seems　not　to　have　happened。　for　over　three　million　years；　lucy　and　herfellow　australopithecines　scarcely　changed　at　all。　their　brain　didn鈥檛　grow　and　there　is　no　signthat　they　used　even　the　simplest　tools。　what　is　stranger　still　is　that　we　now　know　that　forabout　a　million　years　they　lived　alongside　other　early　hominids　who　did　use　tools；　yet　theaustralopithecines　never　took　advantage　of　this　useful　technology　that　was　all　around　them。

at　one　point　between　three　and　two　million　years　ago；　it　appears　there　may　have　been　asmany　as　six　hominid　types　coexisting　in　africa。　only　one；　however；　was　fated　to　last：　homo；which　emerged　from　the　mists　beginning　about　two　million　years　ago。　no　one　knows　quitewhat　the　relationship　was　between　australopithecines　and　homo；　but　what　is　known　is　thatthey　coexisted　for　something　over　a　million　years　before　all　the　australopithecines；　robust　andgracile　alike；　vanished　mysteriously；　and　possibly　abruptly；　over　a　million　years　ago。　no　oneknows　why　they　disappeared。　鈥減erhaps；鈥潯�suggests　matt　ridley；　鈥渨e　ate　them。鈥�

conventionally；　the　homo　line　begins　with　homo　habilis；　a　creature　about　whom　we　knowalmost　nothing；　and　concludes　with　us；　homo　sapiens　（literally　鈥渕an　the　thinker鈥潱�。　inbetween；　and　depending　on　which　opinions　you　value；　there　have　been　half　a　dozen　otherhomo　species：　homo　ergaster；　homo　neanderthalensis；　homo　rudolfensis；　homoheidelbergensis；　homo　erectus；　and　homo　antecessor。

homo　habilis　（鈥渉andy　man鈥潱�　was　named　by　louis　leakey　and　colleagues　in　1964　and　wasso　called　because　it　was　the　first　hominid　to　use　tools；　albeit　very　simple　ones。　it　was　a　fairlyprimitive　creature；　much　more　chimpanzee　than　human；　but　its　brain　was　about　50　percentlarger　than　that　of　lucy　in　gross　terms　and　not　much　less　large　proportionally；　so　it　was　theeinstein　of　its　day。　no　persuasive　reason　has　ever　been　adduced　for　why　hominid　brainssuddenly　began　to　grow　two　million　years　ago。　for　a　long　time　it　was　assumed　that　big　brainsand　upright　walking　were　directly　related鈥攖hat　the　movement　out　of　the　forests　necessitatedcunning　new　strategies　that　fed　off　of　or　promoted　braininess鈥攕o　it　was　something　of　asurprise；　after　the　repeated　discoveries　of　so　many　bipedal　dullards；　to　realize　that　there　wasno　apparent　connection　between　them　at　all。

鈥渢here　is　simply　no　pelling　reason　we　know　of　to　explain　why　human　brains　gotlarge；鈥潯�says　tattersall。　huge　brains　are　demanding　organs：　they　make　up　only　2　percent　of　thebody鈥檚　mass；　but　devour　20　percent　of　its　energy。　they　are　also　paratively　picky　in　whatthey　use　as　fuel。　if　you　never　ate　another　morsel　of　fat；　your　brain　would　not　plainbecause　it　won鈥檛　touch　the　stuff。　it　wants　glucose　instead；　and　lots　of　it；　even　if　it　means　short…changing　other　organs。　as　guy　brown　notes：　鈥渢he　body　is　in　constant　danger　of　beingdepleted　by　a　greedy　brain；　but　cannot　afford　to　let　the　brain　go　hungry　as　that　would　rapidlylead　to　death。鈥潯�a　big　brain　needs　more　food　and　more　food　means　increased　risk。

tattersall　thinks　the　rise　of　a　big　brain　may　simply　have　been　an　evolutionary　accident。　hebelieves　with　stephen　jay　gould　that　if　you　replayed　the　tape　of　life鈥攅ven　if　you　ran　it　backonly　a　relatively　short　way　to　the　dawn　of　hominids鈥攖he　chances　are　鈥渜uite　unlikely鈥潯�thatmodern　humans　or　anything　like　them　would　be　here　now。

鈥渙ne　of　the　hardest　ideas　for　humans　to　accept；鈥潯�he　says；　鈥渋s　that　we　are　not　theculmination　of　anything。　there　is　nothing　inevitable　about　our　being　here。　it　is　part　of　ourvanity　as　humans　that　we　tend　to　think　of　evolution　as　a　process　that；　in　effect；　wasprogrammed　to　produce　us。　even　anthropologists　tended　to　think　this　way　right　up　until　the1970s。鈥潯�indeed；　as　recently　as　1991；　in　the　popular　textbook　the　stages　of　evolution；　c。

loring　brace　stuck　doggedly　to　the　linear　concept；　acknowledging　just　one　evolutionary　deadend；　the　robust　australopithecines。　everything　else　represented　a　straightforwardprogression鈥攅ach　species　of　hominid　carrying　the　baton　of　development　so　far；　then　handingit　on　to　a　younger；　fresher　runner。　now；　however；　it　seems　certain　that　many　of　these　earlyforms　followed　side　trails　that　didn鈥檛　e　to　anything。

luckily　for　us；　one　did鈥攁　group　of　tool　users；　which　seemed　to　arise　from　out　of　nowhereand　overlapped　with　the　shadowy　and　much　disputed　homo　habilis。　this　is　homo　erectus；　thespecies　discovered　by　eug猫ne　dubois　in　java　in　1891。　depending　on　which　sources　youconsult；　it　existed　from　about　1。8　million　years　ago　to　possibly　as　recently　as　twenty　thousandor　so　years　ago。

according　to　the　java　man　authors；　homo　erectus　is　the　dividing　line：　everything　thatcame　before　him　was　apelike　in　character；　everything　that　came　after　was　humanlike。　homoerectus　was　the　first　to　hunt；　the　first　to　use　fire；　the　first　to　fashion　plex　tools；　the　first　toleave　evidence　of　campsites；　the　first　to　look　after　the　weak　and　frail。　pared　with　all　thathad　gone　before；　homo　erectus　was　extremely　human　in　form　as　well　as　behavior；　itsmembers　long…limbed　and　lean；　very　strong　（much　stronger　than　modern　humans）；　and　withthe　drive　and　intelligence　to　spread　successfully　over　huge　areas。　to　other　hominids；　homoerectus　must　have　seemed　terrifyingly　powerful；　fleet；　and　gifted。

erectus　was　鈥渢he　velociraptor　of　its　day；鈥潯�according　to　alan　walker　of　penn　stateuniversity　and　one　of　the　world鈥檚　leading　authorities。　if　you　were　to　look　one　in　the　eyes；　itmight　appear　superficially　to　be　human；　but　鈥測ou　wouldn鈥檛　connect。　you鈥檇　be　prey。鈥�

according　to　walker；　it　had　the　body　of　an　adult　human　but　the　brain　of　a　baby。

although　erectus　had　been　known　about　for　almost　a　century　it　was　known　only　fromscattered　fragments鈥攏ot　enough　to　e　even　close　to　making　one　full　skeleton。　so　it　wasn鈥檛until　an　extraordinary　discovery　in　africa　in　the　1980s　that　its　importance鈥攐r；　at　the　veryleast；　possible　importance鈥攁s　a　precursor　species　for　modern　humans　was　fully　appreciated。

the　remote　valley　of　lake　turkana　（formerly　lake　rudolf）　in　kenya　is　now　one　of　theworld鈥檚　most　productive　sites　for　early　human　remains；　but　for　a　very　long　time　no　one　hadthought　to　look　there。　it　was　only　because　richard　leakey　was　on　a　flight　that　was　divertedover　the　valley　that　he　realized　it　might　be　more　promising　than　had　been　thought。　a　teamwas　dispatched　to　investigate；　but　at　first　found　nothing。　then　late　one　afternoon　kamoyakimeu；　leakey鈥檚　most　renowned　fossil　hunter；　found　a　small　piece　of　hominid　brow　on　a　hillwell　away　from　the　lake。　such　a　site　was　unlikely　to　yield　much；　but　they　dug　anyway　out　ofrespect　for　kimeu鈥檚　instincts　and　to　their　astonishment　found　a　nearly　plete　homo　erectusskeleton。　it　was　from　a　boy　aged　between　about　nine　and　twelve　who　had　died　1。54　millionyears　ago。　the　skeleton　had　鈥渁n　entirely　modern　body　structure；鈥潯�says　tattersall；　in　a　way　thatwas　without　precedent。　the　turkana　boy　was　鈥渧ery　emphatically　one　of　us。鈥�

also　found　at　lake　turkana　by　kimeu　was　knm…er　1808；　a　female　1。7　million　years　old；which　gave　scientists　their　first　clue　that　homo　erectus　was　more　interesting　and　plexthan　previously　thought。　the　woman鈥檚　bones　were　deformed　and　covered　in　coarse　growths；the　result　of　an　agonizing　condition　called　hypervitaminosis　a；　which　can　e　only　fromeating　the　liver　of　a　carnivore。　this　told　us　first　of　all　that　homo　erectus　was　eating　meat。

even　more　surprising　was　that　the　amount　of　growth　showed　that　she　had　lived　weeks　or　evenmonths　with　the　disease。　someone　had　looked　after　her。　it　was　the　first　sign　of　tenderness　inhominid　evolution。

it　was　also　discovered　that　homo　erectus　skulls　contained　（or；　in　the　view　of　some；　possiblycontained）　a　broca鈥檚　area；　a　region　of　the　frontal　lobe　of　the　brain　associated　with　speech。

chimps　don鈥檛　have　such　a　feature。　alan　walker　thinks　the　spinal　canal　didn鈥檛　have　the　sizeand　plexity　to　enable　speech；　that　they　probably　would　have　municated　about　as　wellas　modern　chimps。　others；　notably　richard　leakey；　are　convinced　they　could　speak。

for　a　time；　it　appears；　homo　erectus　was　the　only　hominid　species　on　earth。　it　was　hugelyadventurous　and　spread　across　the　globe　with　what　seems　to　have　been　breathtaking　rapidity。

the　fossil　evidence；　if　taken　literally；　suggests　that　some　members　of　the　species　reached　javaat　about　the　same　time　as；　or　even　slightly　before；　they　left　africa。　this　has　led　some　hopefulscientists　to　suggest　that　perhaps　modern　people　arose　not　in　africa　at　all；　but　in　asia鈥攚hichwould　be　remarkable；　not　to　say　miraculous；　as　no　possible　precursor　species　have　ever　beenfound　anywhere　outside　africa。　the　asian　hominids　would　have　had　to　appear；　as　it　were；spontaneously。　and　anyway　an　asian　beginning　would　merely　reverse　the　problem　of　theirspread；　you　would　still　have　to　explain　how　the　java　people　then　got　to　africa　so　quickly。

there　are　several　more　plausible　alternative　explanations　for　how　homo　erectus　managedto　turn　up　in　asia　so　soon　after　its　first　appearance　in　africa。　first；　a　lot　of　plus…or…minusinggoes　into　the　dating　of　early　human　remains。　if　the　actual　age　of　the　african　bones　is　at　thehigher　end　of　the　range　of　estimates　or　the　javan　ones　at　the　lower　end；　or　both；　then　there　isplenty　of　time　for　african　erects　to　find　their　way　to　asia。　it　is　also　entirely　possible　that　oldererectus　bones　await　discovery　in　africa。　in　addition；　the　javan　dates　could　be　wrongaltogether。

now　for　the　doubts。　some　authorities　don鈥檛　believe　that　the　turkana　finds　are　homoerectus　at　all。　the　snag；　ironically；　was　that　although　the　turkana　skeletons　were　admirablyextensive；　all　othererectus　fossils　are　inconclusively　fragmentary。　as　tattersall　and　jeffreyschwartz　note　in　extinct　humans；　most　of　the　turkana　skeleton　鈥渃ouldn鈥檛　be　pared　withanything　else　closely　related　to　it　because　the　parable　parts　weren鈥檛　known！鈥潯�the　turkanaskeletons；　they　say；　look　nothing　like　any　asian　homo　erectus　and　would　never　have　beenconsidered　the　same　species　except　that　they　were　contemporaries。　some　authorities　insist　oncalling　the　turkana　specimens　（and　any　others　from　the　same　period）　homo　ergaster。

tattersall　and　schwartz　don鈥檛　believe　that　goes　nearly　far　enough。　they　believe　it　wasergaster鈥渙r　a　reasonably　close　relative鈥潯�that　spread　to　asia　from　africa；　evolved　intohomo　erectus；and　then　died　out。

what　is　certain　is　that　sometime　well　over　a　million　years　ago；　some　new；　parativelymodern；　upright　beings　left　africa　and　boldly　spread　out　across　much　of　the　globe。　theypossibly　did　so　quite　rapidly；　increasing　their　range　by　as　much　as　twenty…five　miles　a　year　onaverage；　all　while　dealing　with　mountain　ranges；　rivers；　deserts；　and　other　impediments　andadapting　to　differences　in　climate　and　food　sources。　a　particular　mystery　is　how　they　passedalong　the　west　side　of　the　red　sea；　an　area　of　famously　punishing　aridity　now；　but　even　drierin　the　past。　it　is　a　curious　irony　that　the　conditions　that　prompted　them　to　leave　africa　wouldhave　made　it　much　more　difficult　to　do　so。　yet　somehow　they　managed　to　find　their　wayaround　every　barrier　and　to　thrive　in　the　lands　beyond。

and　that；　i鈥檓　afraid；　is　where