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1、WhatpromptedearlyhumanstoleaveAfricaforthefirsttimeDiscussiononthereasonsandevidenceforthefirsttimethatearlyhumansleftAfricaIntroductionThispaperdiscussesthetopicofnofactorcanexplainthefirsttimethatearlyhumansleftAfrica.Earlyhumansareancienthumansintheearlystageofhumanevolutionfromapestohumans,inclu
2、dingthehumanoidanimalsatthistime.ThefirstdeparturefromAfricareferstothefirstoutwardmigrationofearlyhumanbeingsfromtheAfricancontinent.ThispaperdiscussestheevidenceandreasonsofearlyhumanleavingAfricaforthefirsttimefromthreeaspects:thetestimonyprovidedbyhumanfossils,theevidenceprovidedbyclimatechangea
3、ndthetestimonyprovidedbyhumangeneticmappinganalysis.Thispaperbelievesthattheestablishmentoftheperiodofhumanfossilsandhumanremainsbyarchaeologistscancorroborateeachotherwiththeclimateanalysisandhumangenemapextensionofpaleoclimatology,andcanprovethatearlyhumansleftAfricaforthefirsttimeduetoclimatechan
4、geanddeteriorationoflivingenvironment,andspreadtotheEurasiancontinentandotherterritories.1. DirectevidencefromhumanfossilsHumanfossilsareallthathumanancestorsleftintheworld,andarealsoimportantevidencetorevealthepathandcauseofhumanmigration.In1924,archaeologistsfoundtheoldestancienthumanfossilinalime
5、stonecaveinDrimolen,nearJohannesburg,SouthAfrica,andnameditAustralopithecusAfricanus.Amongmorethan900ancienthumanremains,oneofthemwas3millionyearsago(Dennell,Roebroeks,2005).In1990,researchersfoundtheearliestancienthumanfossilsattheDemanisisiteinGeorgia,whichwereearlierthanthoseinAfrica.Theseskullfo
6、ssilsandbonefossilshavebeenprovedthatancienthumansatthattimewereveryshort,only1.5meterstall,andthebraincapacitywasonlyonethirdofthatofmodernhumans(Agust,Lordkipanidze,2011).TheemergenceoftheDemanianancientsextendedtheearliesttimeofhumanexistenceinAsiato1.8millionyearsago.Later,archaeologistsfoundthe
7、earliestEuropeanfossilsatthearchaeologicalsiteofAtapulcainSpain,whicharehumantoothbonesdatingmorethan1.4millionyearsago(Forster,Matsumura,2005).Accordingtothetimejudgmentofarchaeologistsonthefossilsofancientapesandhumans,noearlierhumanfossilremainshavebeenfoundonthecontinentoutsideAfrica.Fromtheevid
8、enceprovidedbyancienthumanfossils,asearlyas2.5MaBPto3.0MaBPthereweresignsofancienthumanandhumanlifeinAfrica.TheearliestsurvivaltimeofhumanintheSouthCaucasuswas1.7MaBPto1.8MaBP,whiletheevidenceoftheearliesthumanlifeinWesternEuropecouldbeextendedto1.4MaBP(Derricourt,2005).Accordingtothetimejudgmentofa
9、rchaeologistsonthefossilsofancientapesandhumans,noearlierhumanfossilremainshavebeenfoundonthecontinentoutsideAfrica.TheevidenceprovidedbyancienthumanfossilsshowsthattheancienthumanfossilsinthesouthernCaucasusandwesternEuropearemoreadvancedthanthoseofAfricanancienthumansintermsofbraincapacity,heighta
10、ndotheraspects,althoughtheseancienthumansarestillverybackwardcomparedwiththebraincapacity,heightandphysicalabilityofmodernhumans.ThetimepointoftheappearanceofancienthumanfossilscaneffectivelyprovethatAfricansfirstappearedancienthumansandbecametheearliestancestorsofmankind.Stonesandotherearlyinstrume
11、ntsunearthedfromarchaeologicalsitescanalsoprovethatancienthumansandhumanoidanimalslivinginAfricagatheredandmigratedduringtheprocessofforagingandhunting.ThereisnoevidenceofearlierhumanandanimalproliferationinothercontinentsexceptAfrica(Balter,Gibbons,2020).Atthesametime,alargenumberoffossilsfromtheSo
12、uthAfricanGardenfoundintheEastAfricanRiftValley,theeastbankofLakeTurnerinKenya,andtheTanzanianValleyhaveprovedthattheyhavetheabilitytowalkuprightandusesimpletools.TheseevidencescanprovethatearlyhumanbeingshavetheabilitytomigrateandliveingroupsforlongdistancesinAfrica.Itcanthelpthinkingthatearlyhuman
13、beingssetoutfromtheAfricancontinentandcrossedthedesertnorthward,enteredtheCaucasusfromSuez,andfurthermigratedtoIndiaandWesternEurope.ThestoneaxeandothertoolsunearthedinGeorgiaevenprovedthatearlyhumanshadbeenverycruelandviciousintheprocessofleavingtheAfricancontinentandmigratingtotheMiddleEast.Theyev
14、endirectlycompetedwithwildcarnivoresforfood.Therefore,thechronologicalsequence,evolutionarycharacteristicsandthecharacteristicsoftoolsusedbyearlyhumansexcavatedbyarchaeologistsfromallovertheworldcansupporteachotherandsupporttheviewthatearlyhumansleftAfricaforthefirsttime.2. Climatetransformationmake
15、smankindleaveAfricaClimatechangeforcedearlyhumanstoleaveAfricaandbegintomigratebychangingthelivingenvironmentofhumans.AccordingtotheresearchofQuaternarypaleoclimatologists,theglobalpaleoclimatehasundergonesignificantadjustmentbetween2.5and2.8MaBRAtthistime,theearthenteredtheQuaternaryIceAge(Thomas,B
16、urrough,2012).MostofEuropeandNorthAmericabegantofreezerapidly,andmostofthelandinthenorthernhemispherewascoveredbyglaciers.TheScandinavianGlacierCenter,SiberianGlacierCenterandGreenlandGlacierCenterinthenorthernhemispherebegantoextendtothesouth(Timmermann,Friedrich,2016).Theexpansionofglaciersintheno
17、rthernhemispherehasmadetheclimatemovesouthward.Atthesametime,theclimateoftheAfricancontinentbegantobecomeunusuallydry,andtheairhumidityandprecipitationonthecontinentdecreasedrapidly.ThelivingenvironmentofancienthumansontheAfricancontinentisnolongersuitableforhumanhabitationduetotherapiddegradationof
18、vegetationandthedryingupofriversandlakes(Van,2011).Atthesametime,archaeologistshaveprovedthroughhumanfossilsandhumantracesthatearlyhumanbeingscrossedtheSaharaDesertwhenleavingtheAfricancontinentandreachedtheThomasQuarrysiteareainMorocco,NorthAfrica,between1.0MaBPand0.8MaBP(Tierney,Menocal,Zander,201
19、7).Atthesametime,tracesofhumanactivitieswerealsofoundintheGabudPlateauofEthiopiaandAlgeria(Beyin,2006).Inaddition,archaeologistsfoundthatafterleavingAfricaforthefirsttime,earlyhumansmigratedtothemiddleandlowlatitudesofthesubtropicalzonewithawarmerclimateandmoreabundantfood,mainlyincludingthenon-trop
20、icalareasoftheEurasiancontinent.Atthistime,thewinterandnightinhigh-latitudeareasarelonger,andthefoodresourcesareless.Itisdifficultforearlyhumanstoadapttothenewliferhythmandfoodstructure,andmoneycanhardlymigratetohighlatitudeareas.Seekingbenefitsandavoidingharmistheinstinctofhumanbeings.Naturerecords
21、thisattributeinhumangenesthroughhumanevolution.Humanswillnaturallychooseamoresuitableenvironmenttolivein,whichincludesmorefood,sufficientwaterresourcesandasafeenvironment.Likeotheranimals,humanbeingsareverypassiveintheirabilitytoadapttoenvironmentalchanges.ThechangeofclimatedroughtontheAfricancontin
22、entcausedbytheiceagenotonlymovedtheancientpeoplefromthesafetreelifetotheground,butalsomadethepeoplemoveoutofthemorelivablehighlatitudeareaoftherefrigeratorontheAfricancontinentinordertosurvive.PaleoclimatologistscanprovideastrongexplanationfortheglobalclimatechangeduringtheIceAge,especiallythedrough
23、tchangeoftheclimateintheAfricancontinent,forthefirsttimethatearlyhumanslefttheAfricancontinent.Thevegetationdegradationandfoodreductioncausedbyclimatedroughtforcedancienthumanstomigrateandfindtheirnewsettlements.Theinsecurityofmovingfromtreestothegroundmadeancienthumanslearntoliveingroups,whichalsop
24、rovidedsocialconditionsforthemigrationofancienthumans.TheageandcharacteristicsofhumanfossilsfoundbyarchaeologistsinthemiddleandlowlatitudesoutsidetheAfricancontinent,aswellastheunearthedpaleolithictools,canalsofullyprovethelivingconditionsofancienthumanmigrationinordertoavoiddrought,likethoseoftheco
25、ntinentoutsideAfrica.Therefore,thechangesinhumanlivingenvironmentcausedbythearidclimateoftheAfricancontinentintheiceageandthecoldiceclimateinthehighlatituderegionshavebecometheimportantreasonsforhumanmigrationfromtheAfricancontinent.Thefindingsofclimatologistsandarchaeologistsintheirrespectivefields
26、caneffectivelysupporttheseviews.3. HumangenestransmitthepathofhumanmigrationThemappingandanalysisofhumangenescanprovidenewevidenceforearlyhumansleavingAfricaforthefirsttime.In2012,theInternationalGoldResearchGroupmappedandanalyzedthechromosomesof1062menfrom22differentcountriesandregions,includingAus
27、tralia,theUnitedStates,Mali,Sudan,Ethiopia,Japan,PakistanandCambodia.ThescientistsoftheInternationalGenomeResearchGroupanalyzedthedifferenceofYchromosomeofthesemenanddrewthegenepedigreemap.Throughanalysis,theYchromosomeofthesemencanbetracedbacktoAfricaabout1.9millionyearsago.Thatistosay,thesemenhadt
28、hesameAfricanman1.9millionyearsago(Cordaux,Stoneking,2013).Atthesametime,anthropologistshavefoundgenesfromAfricansinthegenesofCairnsaboriginesofAustralianaborigines.ThedenseblackcurlyhairandthicklipsoftheCaimsaborigineswereoriginallythegeneticcodefromAfricaintheirgeneticsequence.DNAinhumancellmitoch
29、ondriaisthecodeusedbynaturetorecordandtransmithumancharacteristics(Reed,Tishkoff,2006).Humannotonlyinheritsthenatureandabilityacquiredbyhumaninthelongnaturalevolutionthroughgenes,butalsochangesinhumanlivingenvironmentandactivitieswillleadtohumangenevariation.Thatistosay,humangenescannotonlyhelptrace
30、humanbeings,butalsodeterminethechangeprocessofhumanlivingenvironmentandlivinghabitsthroughthedifferenceofhumangenes.GenefragmentsfromhumanancestorsofAfricancontinentcanbefoundinhumangenesofdifferentregionsandracesaroundtheworld(Templeton,1997).Thiscanfullyprovethattheearliestancestorofmankindexistsi
31、ntheancientAfricancontinent.Theycontinuetospreadthroughdiffusion,andgraduallyentertheMiddleEast,WesternEurope,EastAsia,NorthAsia,andevenentertheAustralianmainlandtobecomeindigenousresidentshere60000yearsago(Harpending,1993).Thegeneticinheritancepathofthehumangeneticmapandthepathofarchaeologiststolea
32、vetheAfricancontinentandmigrateintheworldforthefirsttimecansupporteachother.ThetimeofhumanskeletonfossilsandthecharacteristicsofhumanremainsfoundbyarchaeologistsatarchaeologicalsitesaroundtheworldcanbethepathofhumanmigrationfromtheAfricancontinenttotheworldforthefirsttime(Semino,1999).Theseevidences
33、caneffectivelyprovethatearlyhumanslefttheAfricancontinentforthefirsttimeandgraduallyoccupiedtheEurasiancontinent,theAmericancontinentandAustralia.TheseevidencescanstronglyprovetheviewthatearlyhumanslefttheAfricancontinentforthefirsttime.4. ConclusionThispaperdiscussesthereasonsandconditionsofearlyhu
34、manleavingAfricaforthefirsttimefromthreeaspects:theevidenceofhumanfossilsdiscoveredbyarchaeologists,theevidenceofclimatechangeintheiceagediscoveredbypaleoclimatologistsandtheevidenceprovidedbyhumangeneticmapping.Archaeologistsfoundthroughthetimetestofhumanfossilsthathumansbegantheirfirstmigrationfro
35、mAfrica2millionyearsago.Accordingtotheevidenceprovidedbymeteorologists,theworldisnowenteringtheQuaternaryIceAge.Thenorthernhemispherebegantobecoveredbyglaciersandbecamecold,whiletheAfricancontinentbecameextremelydry.ClimatechangeforcedearlyhumanstomigratefromtheAfricancontinenttothemiddleandlowlatit
36、udesoftheEurasiancontinent.HumanfossilsfoundbyarchaeologistsinGeorgiaandWesternEuropecanalsoprovethatatthistime,earlyhumansbegantomigratefromtheAfricancontinenttotheMiddleEastandWesternEurope.Thisisinlinewiththeneedsofearlyhumanbeingsforthelivingenvironment.Theanalysisofthehumangeneticmapcanprovetha
37、ttoday,peopleofdifferentracesindifferentregionshavethesameAfricanancestry.ThisprovesthatthescatteredhumanbeingsallovertheworldcomefromtheancientAfricancontinent.TheseevidencescanproveandexplainthatearlyhumansleftAfricaforthefirsttime.ReferenceListDennell,R.,Roebroeks,W.(2005).4AnAsianperspectiveonea
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