3.2CivilizationBetween4000and3000B.C.,significanttechnologicaldevelopmentsbegantotransformtheNeolithictowns.Theinventionofwritingenabledrecordstobekept,andtheuseofmetalsmarkedanewlevelofhumancontrolovertheenvironmentanditsresources.Alreadybefore4000B.C.,craftspeoplehaddiscoveredthatmetal-bearingrockscouldbeheatedtoliquefymetals,whichcouldthenbecastinmoldstoproducetoolsandweaponsthatweremoreusefulthanstoneinstruments.Althoughcopperwasthefirstmetaltobeutilizedinproducingtools,after4000B.C.craftspeopleinwesternAsiadiscoveredthatacombinationofcopperandtinproducedbronze,amuchharderandmoredurablemetalthancopper.ItswidespreadusehasledhistorianstospeakofaBronzeAgefromaround3000to1200B.C.,whenbronzewasincreasinglyreplacedbyiron.Atfirst,Neolithicsettlementswerehardlymorethanvillages.Butastheirinhabitantsmasteredtheartoffarming,theygraduallybegantogivebirthtomorecomplexhumansocieties.Aswealthincreased,suchsocietiesbegantodeveloparmiesandtobuildwalledcities.BythebeginningoftheBronzeAge,theconcentrationoflargernumbersofpeopleintherivervalleysofMesopotamiaandEgyptwasleadingtoawholenewpatternforhumanlife.Aswehaveseen,earlyhumanbeingsformedsmallgroupsthatdevelopedasimpleculturethatenabledthemtosurvive.Ashumansocietiesgrewanddevelopedgreatercomplexity,anewformofhumanexistence-calledcivilization-cameintobeing.Acivilizationisacomplexcultureinwhichlargenumbersofhumanbeingsshareanumberofcommonelements.Historianshaveidentifiedanumberofbasiccharacteristicsofcivilization,mostofwhichareevidentintheMesopotamianandEgyptiancivilizations.Theseinclude(1)anurbanrevolution;citiesbecamethefocalpointsforpolitical,economic,social,cultural,andreligiousdevelopment;(2)adistinctreligiousstructure;thegodsweredeemedcrucialtothecommunity’ssuccess,andprofessionalpriestlyclasses,asstewardsofthegods’property,regulatedrelationswiththegods;(3)newpoliticalandmilitarystructures;anorganizedgovernmentbureaucracyarosetomeettheadministrativedemandsofthegrowingpopulationwhilearmieswereorganizedtogainlandandpower;(4)anewsocialstructurebasedoneconomicpower;whilekingsandanupperclassofpriests,politicalleaders,andwarriorsdominated,therealsoexistedlargegroupsoffreepeople(farmers,artisans,craftspeople)andattheverybottom,socially,aclassofslaves;(5)thedevelopmentofwriting;kings,priests,merchants,andartisansusedwritingtokeeprecords;and(6)newformsofsignificantartisticandintellectualactivity,suchasmonumentalarchitecturalstructures,usuallyreligious,occupiedaprominentplaceinurbanenvironments.Whyearlycivilizationsdevelopedremainsdifficulttoexplain.SincecivilizationsdevelopedindependentlyinIndia,China,Mesopotamia,andEgypt,cangeneralcausesbeidentifiedthatwouldexplainwhyallofthesecivilizationsemerged?Anumberofpossibleexplanationsofthebeginningofcivilizationhavebeensuggested.Atheoryofchallengeandresponsemaintainsthatchallengesforcedhumanbeingstomakeeffortsthatresultedintheriseofcivilization.Somescholarshaveadheredtoamaterialexplanation.Materialforces,suchasthegrowthoffoodsurpluses,madepossiblethespecializationoflaboranddevelopmentoflargecommunitieswithbureaucraticorganization.ButtheareaoftheFertileCrescent,inwhichMesopotamiancivilizationemerged,wasnotnaturallyconducivetoagriculture.Abundantfoodcouldonlybeproducedwithamassivehumanefforttocarefullymanagethewater,aneffortthatcreatedtheneedfororganizationandbureaucraticcontrolandledtocivilizedcities.Somehistorianshavearguedthatnonmaterialforces,primarilyreligious,providedthesenseofunityandpurposethatmadesuchorganizedactivitiespossible.Finally,somescholarsdoubtthatwearecapableofeverdiscoveringtheactualcausesofearlycivilization.