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in thEBirth orDErBook why youArE thE wAy youArE (2004),Dr. kEvin lEmAn notEs thAt 21 oF thE First 23AmEriCAns in spACE wErE First-Born mAlEs or only ChilDrEn. morE thAn hAlF oF unitED stAtEs prEsiDEnts hAvE BEEn First-Borns or First-Born Boys. it’s A prEtty signiFiCAnt FinDing historiCAlly, BECAusE FAmiliEs usED to BE BiggEr thAn thEy ArE toDAy. in ADDition to BEing high AChiEvErs, olDEr ChilDrEn Also gEnErAlly hAvE highEr iqs (智商) thAn youngEr onEs. rEsEArChErs hAvE notED thAt thE morE kiDs A FAmily hAs, thE lowEr EACh ChilD’s inDiviDuAl iq tEnDs to BE. thEy givE A FEw rEAsons For this. pArEnts only hAvE so muCh timE, AttEntion, AnD monEy. thE morE kiDs thEy hAvE, thE morE thEsE things ArE DiviDED、First-Borns initiAlly gEt thE EntirE pArEntAl-timE piE. whAt’s morE, thE rAtio oF grown-ups to kiDs DECrEAsEs with EACh nEw BABy. {{u}}so thE youngEr onEs ArE surrounDED By morE ChilDrEn’s lAnguAgE on AvErAgE thAn thE olDEr kiDs{{/u}}. somE rEsEArChErs think pArEntAl AttEntion is thE kEy to pErsonAlity Birth-orDEr DiFFErEnCEs. in his BookBorn to rEBEl, psyChologist FrAnk sullowAy sAys CompEtition For mom AnDDAD’s AttEntion is thE thing thAt rEAlly shApEs our pErsonAlitiEs AnD, in FACt hAs shApED history. hE ArguEs thAt wE ADApt our pErsonAlitiEs As pArt oF our strAtEgy to sEEk FAvor From mom AnDDAD、youngEr siBlings (兄弟姐妹) tEnD to BEComE rEBEls. sullowAy stuDiED politiCAl ACtivists AnD FounD thAt lAtEr-Born ACtivists wErE morE rADiCAl thAn thEir First-Born pEErs. thE ConClusion oF his Book is thAt siBling CompEtition For pArEntAl AttEntion CAn AFFECt soCiEty As A wholE in timEs oF rEvolution. thomAs jEFFErson, kArl mArx, AnD FiDElCAstro wErE All youngEr siBlings, For ExAmplE. As CompElling As this All is, it’s Also somEthing wE shoulD proBABly tAkE with CAution, thErE ArE othEr things thAt hAppEn to us in liFE BEsiDEs thE ADDition oF siBlings to our FAmiliEs.A、pArEnt CAn DiE; A hurriCAnE CAn lEAvE us homElEss; wE CAn CAtCh A liFE-thrEAtEning DisEAsE.Any onE oF thEsE things will proBABly hAvE morE oF An EFFECt on our pErsonAlitiEs thAn thE prEsEnCE oF siBlings. A、2002 stuDy BorE this out.AFtEr intErviEwing 535 unDErgrADuAtEs, rEsEArChErs ConCluDED thAt pErsonAlity DiFFErEnCEs rElAtED to Birth orDEr wErE "FolklorE", Although iq AnD AChiEvEmEnt DiFFErEnCEs wErE wiDEly supportED By rEsEArCh.

whiCh oF thE Following is not mEntionED As A FACtor shAping pErsonAlityA．DEAth oF A pArEnt.
B．ChilDrEn’s lAnguAgE.
C．A、nAturAl DisAstEr.
D．A、FAtAl DisEAsE.