《A Short History of Nearly Everything》第152章

to　prove；　or　disprove；　from　fossils。　in　1999；　archeologists　in　portugal　found　theskeleton　of　a　child　about　four　years　old　that　died　24；500　years　ago。　the　skeleton　was　modernoverall；　but　with　certain　archaic；　possibly　neandertal；　characteristics：　unusually　sturdy　legbones；　teeth　bearing　a　distinctive　“shoveling”　pattern；　and　（though　not　everyone　agrees　on　it）an　indentation　at　the　back　of　the　skull　called　a　suprainiac　fossa；　a　feature　exclusive　toneandertals。　erik　trinkaus　of　washington　university　in　st。　louis；　the　leading　authority　onneandertals；　announced　the　child　to　be　a　hybrid：　proof　that　modern　humans　and　neandertalsinterbred。　others；　however；　were　troubled　that　the　neandertal　and　modern　features　weren’tmore　blended。　as　one　critic　put　it：　“if　you　look　at　a　mule；　you　don’t　have　the　front　endlooking　like　a　donkey　and　the　back　end　looking　like　a　horse。”
ian　tattersall　declared　it　to　be　nothing　more　than　“a　chunky　modern　child。”　he　accepts　thatthere　may　well　have　been　some　“hanky…panky”　between　neandertals　and　moderns；　butdoesn’t　believe　it　could　have　resulted　in　reproductively　successful　offspring。
1“i　don’t　knowof　any　two　organisms　from　any　realm　of　biology　that　are　that　different　and　still　in　the　samespecies；”　he　says。
with　the　fossil　record　so　unhelpful；　scientists　have　turned　increasingly　to　genetic　studies；in　particular　the　part　known　as　mitochondrial　dna。　mitochondrial　dna　was　only　discoveredin　1964；　but　by　the　1980s　some　ingenious　souls　at　the　university　of　california　at　berkeley　hadrealized　that　it　has　two　features　that　lend　it　a　particular　convenience　as　a　kind　of　molecularclock：　it　is　passed　on　only　through　the　female　line；　so　it　doesn’t　bee　scrambled　withpaternal　dna　with　each　new　generation；　and　it　mutates　about　twenty　times　faster　than　normalnuclear　dna；　making　it　easier　to　detect　and　follow　genetic　patterns　over　time。　by　tracking　therates　of　mutation　they　could　work　out　the　genetic　history　and　relationships　of　whole　groups　ofpeople。
in　1987；　the　berkeley　team；　led　by　the　late　allan　wilson；　did　an　analysis　of　mitochondrialdna　from　147　individuals　and　declared　that　the　rise　of　anatomically　modern　humansoccurred　in　africa　within　the　last　140；000　years　and　that　“all　present…day　humans　aredescended　from　that　population。”　it　was　a　serious　blow　to　the　multiregionalists。　but　thenpeople　began　to　look　a　little　more　closely　at　the　data。　one　of　the　most　extraordinary　points—almost　too　extraordinary　to　credit　really—was　that　the　“africans”　used　in　the　study　wereactually　african…americans；　whose　genes　had　obviously　been　subjected　to　considerablemediation　in　the　past　few　hundred　years。　doubts　also　soon　emerged　about　the　assumed　ratesof　mutations。
by　1992；　the　study　was　largely　discredited。　but　the　techniques　of　genetic　analysiscontinued　to　be　refined；　and　in　1997　scientists　from　the　university　of　munich　managed　toextract　and　analyze　some　dna　from　the　arm　bone　of　the　original　neandertal　man；　and　thistime　the　evidence　stood　up。　the　munich　study　found　that　the　neandertal　dna　was　unlike　anydna　found　on　earth　now；　strongly　indicating　that　there　was　no　genetic　connection　betweenneandertals　and　modern　humans。　now　this　really　was　a　blow　to　multiregionalism。
1one　possibility　is　that　neandertals　and　cro…magnons　had　different　numbers　of　chromosomes；　a　plicationthat　monly　arises　when　species　that　are　close　but　not　quite　identical　conjoin。　in　the　equine　world；　forexample；　horses　have　64　chromosomes　and　donkeys　62。　mate　the　two　and　you　get　an　offspring　with　areproductively　useless　number　of　chromosomes；　63。　you　have；　in　short；　a　sterile　mule。
then　in　late　2000　nature　and　other　publications　reported　on　a　swedish　study　of　themitochondrial　dna　of　fifty…three　people；　which　suggested　that　all　modern　humans　emergedfrom　africa　within　the　past　100；000　years　and　came　from　a　breeding　stock　of　no　more　than10；000　individuals。　soon　afterward；　eric　lander；　director　of　the　whiteheadinstitute/massachusetts　institute　of　technology　center　for　genome　research；　announced　thatmodern　europeans；　and　perhaps　people　farther　afield；　are　descended　from　“no　more　than　afew　hundred　africans　who　left　their　homeland　as　recently　as　25；000　years　ago。”
as　we　have　noted　elsewhere　in　the　book；　modern　human　beings　show　remarkably　littlegenetic　variability—“there’s　more　diversity　in　one　social　group　of　fifty…five　chimps　than　inthe　entire　human　population；”　as　one　authority　has　put　it—and　this　would　explain　why。
because　we　are　recently　descended　from　a　small　founding　population；　there　hasn’t　been　timeenough　or　people　enough　to　provide　a　source　of　great　variability。　it　seemed　a　pretty　severeblow　to　multiregionalism。　“after　this；”　a　penn　state　academic　told　the　washington　post；“people　won’t　be　too　concerned　about　the　multiregional　theory；　which　has　very　littleevidence。”
but　all　of　this　overlooked　the　more　or　less　infinite　capacity　for　surprise　offered　by　theancient　mungo　people　of　western　new　south　wales。　in　early　2001；　thorne　and　his　colleaguesat　the　australian　national　university　reported　that　they　had　recovered　dna　from　the　oldest　ofthe　mungo　specimens—now　dated　at　62；000　years—and　that　this　dna　proved　to　be“genetically　distinct。”
the　mungo　man；　according　to　these　findings；　was　anatomically　modern—just　like　you　andme—but　carried　an　extinct　genetic　lineage。　his　mitochondrial　dna　is　no　longer　found　inliving　humans；　as　it　should　be　if；　like　all　other　modern　people；　he　was　descended　from　peoplewho　left　africa　in　the　recent　past。
“it　turned　everything　upside　down　again；”　says　thorne　with　undisguised　delight。
then　other　even　more　curious　anomalies　began　to　turn　up。　rosalind　harding；　a　populationgeneticist　at　the　institute　of　biological　anthropology　in　oxford；　while　studying　betaglobingenes　in　modern　people；　found　two　variants　that　are　mon　among　asians　and　theindigenous　people　of　australia；　but　hardly　exist　in　africa。　the　variant　genes；　she　is　certain；arose　more　than　200；000　years　ago　not　in　africa；　but　in　east　asia—long　before　modern　homosapiens　reached　the　region。　the　only　way　to　account　for　them　is　to　say　that　ancestors　ofpeople　now　living　in　asia　included　archaic　hominids—java　man　and　the　like。　inte