《A Short History of Nearly Everything》第146章

i　had　been　told　that　they　were　posed　like　that　because　during　the　building　of　the　dioramathe　female　figure　kept　toppling　over；　but　ian　tattersall　insists　with　a　laugh　that　the　story　isuntrue。　“obviously　we　don’t　know　whether　the　male　had　his　arm　around　the　female　or　not；but　we　do　know　from　the　stride　measurements　that　they　were　walking　side　by　side　and　closetogether—close　enough　to　be　touching。　it　was　quite　an　exposed　area；　so　they　were　probablyfeeling　vulnerable。　that’s　why　we　tried　to　give　them　slightly　worried　expressions。”
i　asked　him　if　he　was　troubled　about　the　amount　of　license　that　was　taken　in　reconstructingthe　figures。　“it’s　always　a　problem　in　making　re…creations；”　he　agreed　readily　enough。　“youwouldn’t　believe　how　much　discussion　can　go　into　deciding　details　like　whether　neandertalshad　eyebrows　or　not。　it　was　just　the　same　for　the　laetoli　figures。　we　simply　can’t　know　thedetails　of　what　they　looked　like；　but　we　can　convey　their　size　and　posture　and　make　somereasonable　assumptions　about　their　probable　appearance。　if　i　had　it　to　do　again；　i　think　i　mighthave　made　them　just　slightly　more　apelike　and　less　human。　these　creatures　weren’t　humans。
they　were　bipedal　apes。”
until　very　recently　it　was　assumed　that　we　were　descended　from　lucy　and　the　laetolicreatures；　but　now　many　authorities　aren’t　so　sure。　although　certain　physical　features　（theteeth；　for　instance）　suggest　a　possible　link　between　us；　other　parts　of　the　australopithecineanatomy　are　more　troubling。　in　their　book　extinct　humans；　tattersall　and　schwartz　point　outthat　the　upper　portion　of　the　human　femur　is　very　like　that　of　the　apes　but　not　of　theaustralopithecines；　so　if　lucy　is　in　a　direct　line　between　apes　and　modern　humans；　it　meanswe　must　have　adopted　an　australopithecine　femur　for　a　million　years　or　so；　then　gone　back　toan　ape　femur　when　we　moved　on　to　the　next　phase　of　our　development。　they　believe；　in　fact；that　not　only　was　lucy　not　our　ancestor；　she　wasn’t　even　much　of　a　walker。
“lucy　and　her　kind　did　not　loote　in　anything　like　the　modern　human　fashion；”　insiststattersall。　“only　when　these　hominids　had　to　travel　between　arboreal　habitats　would　they　findthemselves　walking　bipedally；　‘forced’　to　do　so　by　their　own　anatomies。”　johanson　doesn’taccept　this。　“lucy’s　hips　and　the　muscular　arrangement　of　her　pelvis；”　he　has　written；　“wouldhave　made　it　as　hard　for　her　to　climb　trees　as　it　is　for　modern　humans。”
matters　grew　murkier　still　in　2001　and　2002　when　four　exceptional　new　specimens　werefound。　one；　discovered　by　meave　leakey　of　the　famous　fossil…hunting　family　at　laketurkana　in　kenya　and　called　kenyanthropus　platyops　（“kenyan　flat…face”）；　is　from　about　thesame　time　as　lucy　and　raises　the　possibility　that　it　was　our　ancestor　and　lucy　was　anunsuccessful　side　branch。　also　found　in　2001　were　ardipithecus　ramidus　kadabba；　dated　atbetween　5。2　million　and　5。8　million　years　old；　and　orrorin　tugenensis；　thought　to　be　6　millionyears　old；　making　it　the　oldest　hominid　yet　found—but　only　for　a　brief　while。　in　the　summerof　2002　a　french　team　working　in　the　djurab　desert　of　chad　（an　area　that　had　never　beforeyielded　ancient　bones）　found　a　hominid　almost　7　million　years　old；　which　they　labeledsahelanthropus　tchadensis。　（some　critics　believe　that　it　was　not　human；　but　an　early　ape　andtherefore　should　be　called　sahelpithecus。）　all　these　were　early　creatures　and　quite　primitivebut　they　walked　upright；　and　they　were　doing　so　far　earlier　than　previously　thought。
bipedalism　is　a　demanding　and　risky　strategy。　it　means　refashioning　the　pelvis　into　a　fullload…bearing　instrument。　to　preserve　the　required　strength；　the　birth　canal　must　beparatively　narrow。　this　has　two　very　significant　immediate　consequences　and　one　longer…term　one。　first；　it　means　a　lot　of　pain　for　any　birthing　mother　and　a　greatly　increased　dangerof　fatality　to　mother　and　baby　both。　moreover　to　get　the　baby’s　head　through　such　a　tightspace　it　must　be　born　while　its　brain　is　still　small—and　while　the　baby；　therefore；　is　stillhelpless。　this　means　long…term　infant　care；　which　in　turn　implies　solid　male–female　bonding。
all　this　is　problematic　enough　when　you　are　the　intellectual　master　of　the　planet；　but　whenyou　are　a　small；　vulnerable　australopithecine；　with　a　brain　about　the　size　of　an　orange；3therisk　must　have　been　enormous。
3absolute　brain　size　does　not　tell　you　everything…or　possibly　sometimes　even　much。　elephants　and　whales　bothhave　brains　larger　than　ours；　but　you　wouldnt　have　much　trouble　outwitting　them　in　contract　negotiations。　it　isrelative　size　that　matters；　a　point　that　is　often　overlooked。　as　gould　notes；　a。　africanus　had　a　brain　of　only　450cubic　centimeters；　smaller　than　that　of　a　gorilla。　but　a　typical　africanus　male　weighed　less　than　a　hundredpounds；　and　a　female　much　less　still；　whereas　gorillas　can　easily　top　out　at　600　pounds　（gould　pp。　181…83）。
so　why　did　lucy　and　her　kind　e　down　from　the　trees　and　out　of　the　forests？　probablythey　had　no　choice。　the　slow　rise　of　the　isthmus　of　panama　had　cut　the　flow　of　waters　fromthe　pacific　into　the　atlantic；　diverting　warming　currents　away　from　the　arctic　and　leading　tothe　onset　of　an　exceedingly　sharp　ice　age　in　northern　latitudes。　in　africa；　this　would　haveproduced　seasonal　drying　and　cooling；　gradually　turning　jungle　into　savanna。　“it　was　not　somuch　that　lucy　and　her　like　left　the　forests；”　john　gribbin　has　written；　“but　that　the　forestsleft　them。”
but　stepping　out　onto　the　open　savanna　also　clearly　left　the　early　hominids　much　moreexposed。　an　upright　hominid　could　see　better；　but　could　also　be　seen　better。　even　now　as　aspecies；　we　are　almost　preposterously　vulnerable　in　the　wild。　nearly　every　large　animal　youcan　care　to　name　is　stronger；　faster；　and　toothier　than　us。　faced　with　attack；　modern　humanshave　only　two　advantages。　we　have　a　good　brain；　with　which　we　can　devise　strategies；　andwe　have　hands　with　which　we　can　fling　or　brandish　hurtful　objects。　we　are　the　only　creaturethat　can　harm　at　a　distance。　we　can　thus　afford　to　be　physically　vulnerable。
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。　fo