Demographic Transition Egeo 312 1 DEMOGRAPHIC TRANSITION MODEL.
Rethinking the Demographic Transition
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Transcript of Rethinking the Demographic Transition
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RethinkingtheDemographicTransitionRethinkingtheDemographicTransitionRethinkingtheDemographicTransitionRethinkingtheDemographicTransitionEdwardHugh
BarcelonaJanuary2006BarcelonaJanuary2006BarcelonaJanuary2006BarcelonaJanuary2006FirstDraftOnly,NotForQuotingFirstDraftOnly,NotForQuotingFirstDraftOnly,NotForQuotingFirstDraftOnly,NotForQuotingItwasthelateImreLakatoswhousedtoarguethattheimportantquestiontoaskaboutanyresearchprogramwaswhetheritwasinitsprogressiveorinitsdegenerativestage.ForLakatosaprogressiveresearchprogramwascharacterisedbygrowthandthediscoveryofnewandinterestingfactswhilstadegenerativeonewasmarkedbyalackofgrowth,andbyan
excessiveincreaseinwhathetermedthe"protectivebelt"whichsurroundstheprogram,andinparticularadegenerativeprogrammeisonewhichfindsitselfcontinuallyforcedtorespondtoanever-growinglistofcounter-examplesandnuances(Lakatos,2000.1976,1970).Onthisviewauxiliaryhypothesesfinallyend-upbeingtacked-ontotheoriginaltheoryinanincreasinglyadhoc-ocraticfashion.Atsomestageintheprocessaturningpointisreachedwhereitbecomeson-balancemoreandmoreinterestingtoabandontheoldandbreak-openthenew.Whathasallofthisgottodowithdemographictransitiontheory,well,Ithinkposingthequestionisalready,atleastinpart,toanswerit.
WhatIwillseektoargueinwhatfollowsisthataseriousargumentcannowbemountedthatthetimehascometoatleastaskourselvesthequestionwhethertheoriginaltheoryofthedemographictransitionmaynothavenowpassedintowhatLakatoswouldhavetermeditsdegenerativephase.Thetimehascome,andinmanywaysthequestionhasalreadybeenasked.InanintriguingandthoughtprovokingpaperPeterMcDonaldasks,whatis,averypertinentquestion:Thesearchforacommonsetofconditionsthatwillprevailineverysociety
asitexperiencestheonsetoffertilitydeclineisnecessarilyfruitlessbecausetheextentofvariationineconomies,cultures,socialandpoliticalstructuresandhealthconditionsofdifferentsocietiesattheonsetoffertilitydeclineisclearlyvast.Whywouldweexpectthatasingleexplanationcouldbefoundtocoverthisvastarrayofsituations?(McDonald,2001).Whyindeed?McDonaldsresposetothefactthatithasprovedimpossibletoidentifyanysinglevariablewhichcanexplainsuchanarrayofsituationsis,inmyopinion,tocedegroundunnecessarily,andasascientificmethodologyreasonablerobustdefenceofthehighgroundmightbeabetterapproach.Now,McDonaldargues,isnottheeraofgrandtheories,whichinanyevent
mayoftenturnouttobemorevaccuousthaninformative.Farbetter,hesuggests,wouldbetoengageinwhatRobertMertondescribedasthesearch
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formiddle-rangetheories(Merton1957).Thiswillnotbetheapproachwhichistakenhere,evenifmypointofdepartureissomewhatsimilartothatofMcDonald.AireyandWilsonnotethatOnereactiontothelackofresilienceoftransitiontheorytoempiricaltestinghasbeentotakethetheorytoanevengranderlevel(AireyandWilson)anddespitetheevidentrisksthisis
preciselywhatIwilltrytodo,notabandonthetheory,butincorporateitinawidermoregeneraltheory,orintheterminologyofImreLakatos,inanewresearchprogramme.Certainly,basingouselvessolelyonsimpleOccamitecriteriaitisnottoohardtoarguethatthe"protectivebelt"whichadornstransitiontheoryhasbeengrowingratherrapidlyoflate,andthatsomekindofsimplificationprocessmightbecalledfor.Equallyitcouldbesaidthatthetheory,ratherthanexplainingtoolittle,infactexplainstoomuch.ThistoomuchfactorwasaptlysummedupbyHirschmanwhenhehetartlyobserveredthattransitiontheoryhasroomforeverycausalvariable(Hirschman,1994,211).Whilst
heedingcarefullysuchstricturesweshouldnotgosofarasLivvi-Bacciwho,itwillberecalled,oncedeclaredthat"weshouldjustdestroyallthisnonsenseoftransitiontheory."(citedinCoale1994).RatherletusheedthespiritofAnselyCoalewhowrotethatfertilityreduction"cannotyetbeexplainedbyanysimpleuniversallyvalidmodelorgeneralizeddescription..."(Coale1967).Thekeywordhereshouldbeyet.
ProblemsWithTheConceptProblemsWithTheConceptProblemsWithTheConceptProblemsWithTheConcept
Incontemporarysocialsciencewhenpeoplethinkdemographictransitiontheytendtothinkofaprocesswhichworksinphases,andmosttypicallytherearefoursuchphases(Lee,2003).Infact,demographictransitiontheoryappearstohavebeenconceptualisedinphasesrightfromthestart,withWarrenS.Thompsonsclassic,"Population",paperbreakingdemographicchangedownintoevolutionarystagesaccordingtothevariouslevelslevelsofthebirth,deathandnaturalgrowthrates.Thompsoninfactclassifiedcountriesintothreegroups(groupsA,BandC)basedonthetrendsintheirratesofnaturalpopulationincrease.HeassumedthatcountrieswouldprogressfromGroupC(highbirthanddeathrates)toGroupB(highbirthratesbutdecliningdeathrates)toGroupA(lowbirthanddeathrates,
seeThompson,1929).Thiswasthenatransitioninthreephaes.Subsequently,andinparticularinthewakeofthegrowingawarenessthattherewasisnonaturalend-pointforfertilityatthereplacement-reproductionlevel,thephasestructurewasammended,andanewsecondtransitionwasadded(VandeKaa,1987,Lestaeghe,1995).Morerecently-intheworkofKohler,BillariandOrtega-athird,discrete,'postponement'transitionhasbeenproposed(Kohleretal,2003).Atwhatstage,weareentitledtoask,willallthiscometoanend?Justhowmanytransitionsaretheregoingtobe?Attheveryleastthistendencytospawnphasesandsub-oradditional-
transitionshasbecomeincreasinglyaestheticallyirritatingand,inanyevent,itwouldseemtoviolateoneofEinstein'skeymethodologicalprescriptionsfor
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anyusefultheory:thatitbeassimpleasthecomplexityoftheproblemallows.Asfertilitycontinuestodecline,andlifeexpectancycontinuestorisethearrayofspecialcasepleadingsandimprovisedadd-onsofferedtoenablethe
theorytoexplaineachnewphenomenonwhicharriveshasbecomeevermoreexotic,andyet,asWolfgangLutzsorighlysays(Lutzetal,2005),wehavenosoundtheoreticalreasonforassumingthatanygivenleveloffertilityiseitherhomeostaticoracandidateinandofitselfforconstitutingabottomlimit.AtthesametimeJamesVaupelhasargued,andwithequaljustification,thatthereisseeminglynoevidentnaturallimittothehumanlifespan(Vaupel,2004).Infactgloballifeexpectancyhasmorethandoubledoverthepasttwohundredyears,climbingfromanestimated25yearsin1800,tothepresent
levelof65formenand70forwomen(Riley2001).Maximumlifeexpectancyhasrisensteadilybymorethantwoyearsadecade(OeppenandVaupel,2002),adramaticimprovementwhichindicatesthatwemayneedtolookfornewanswerstooldquestionsaboutprogrammedsenescenceandthepresenceofbiologicallydeterminedmaximallife-spans(WachterandFinch1997;Austad1999).Althoughmuchoftheincreaseinlifeexpectancyinthe19thcenturymaybeattributabletoacombinationofbettersanitation,modernmedicine,andimproveddiets,thereisaconsiderableamountofevidencethatthegeneralpatternofalonglifespanisnotuniquetothepastcentury,andthatcurrent
increasesinlifespanmaybeaconsequenceofamoregeneralplasticityinourevolvedhumanlifehistory.Thereisalsogrowingevidencethatlivingintooldageisnotuniquetomodernpopulations,ortoeventhosewhohavehadaccesstosystematicagriculture(cf.Washburn1981).Dataamongextantforagerswithlittleornoaccesstomedicalattentionnormodernfoods,includinggroupslikethe!Kung,theAche,andtheHadza,showthatwomenwhosurviveto45cansubsequentlyexpecttoliveanadditional20-22years,evenifmeanlifeexpectanciesatbirthremaininthe30-37range(BlurtonJonesetal.2002).Extrapolationsbasedoncomparativeanalysesofbrainweightsandbody
sizesamongnon-humanprimatessuggestamaximumlifespanbetween66-78forHomoSapiens(HammerandFoley1996).Thereisalsomountingevidencethatestimatesoflifespanamongextantforagersdepictauniquelifehistorycharacteristicthatcannotbeexplainedasanartifactofmodernconditions(BlurtonJonesetal.2002).Howeverthisgrowingawarenessamongdemographersthatthedemographictransitionasinitiallyconceivedmaycontainmoreintrinsiclimitationsthanwasfirstrecognisedcertainlyhasnotalwayspercolateddowntonon-demographersworkingwithappliedversionsofthetransitiontheory,andin
particular,ithasnotyetpassedundertheradarofmanypracticingeconomists.DespiteLeibensteinsstatementthat:
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"WhilethetheoryoftheDemographicTransitionisofimportancetodemographers(includingthosetrainedaseconomists),itisnotthesortoftheorythatfitsthemind-setoftheoreticallytrainedeconomists.Itwas,andis,inaverydifferentintellectualmoldthanmicroeconomictheory.Forthemost
partitseemslikeagrandhistoricalgeneralizationbuttressedbyavarietyofadhoccausalassertions."(Leibenstein,1974)
thedemographictransitionisstillanotionwhichiswidelyacceptedineconomicsgrowththeory..CharlesJones,intermswhichshouldbeseenasthenormratherthantheexceptionincontemporaryeconomicgrowththeory,putsitlikethis:AssummarizedbyCohen(1995)andEasterlin(1996),thedemographictransitionconsistsoftwophases.Inthefirst,calledamortalityrevolution,mortalityratesfallsharply,whilebirthrateseitherremainrelativelyconstant
orperhapsevenriseslightly.Theresultisanincreaseinthepopulationgrowthrate.Thesecondphaseisthefertilityrevolution,characterizedbyabirthratethatnowfallsmorequicklythantherelativelylowbutstilldecliningmortalityrate.Theresultisadeclineinthepopulationgrowthrate.Thisideathatthedemographictransitionimpliesamortalityratewhichremainsbelowadecliningbutultimatelystabilisingfertilityratewasacoreassumptionoftheoriginaltransitiontheory,andtheideaofreplacementlevelhomeostasiscoupledwithslowlyrisinglifeexpectancycontinuestoenjoywideacceptancetoday,despitethefactthatanincreasingnumberofcounter-examplestothispossibilitymaybereadilyidentified,andthenumberofthese
counter-examplesseemssettogrowratherthandeclineovertheyearstocome.TheliteraturesurroundingthepostWorldWarIIfertilitydeclinehasbeenrichandvaried,anddemographersarestillfarfromachievinganykindofconsensusonpreciselywhichfactorsareresponsiblefortriggeringandsustainingit(BulataoandCasterline,2001;Casterline,2001).Oneauthordescribesthevarietyofcircumstancesunderwhichfertilitydeclinehasoccurredasbewilderingsinceithasoccured"bothwheneconomicconditionshavebeenimprovingandwhentheyhavedeteriorated;inpopulationswithhighstandardsoflivingandinthosewherelivingstandards
arelow;incountrieswithstronglinkstotheglobalconsumercultureandinthosewheresuchlinksareweak;andtotopitallithashashappenedunderthewidestimaginablearrayofpoliticalregimesandpolicysettings"(Cleland2001).Wherethenmaywelookforthecommonthreadinthisstory?Wherethenmaywelookforthecommonthreadinthisstory?Wherethenmaywelookforthecommonthreadinthisstory?Wherethenmaywelookforthecommonthreadinthisstory?Togetrighttotheheartoftheissue,oneoftheprincipalproblemswithclassicdemographictransitiontheorytheorymaywelllieinthescopeofthe
theoryitselfandinthefactthatitstookasitsstartingpointtheonsetofmodernitywiththearrivaloftheprocesswhichsubsequentlybecameknown
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astheindustrialrevolution.Assuchthetheorymayhavebecomethevictimofitsowninitialcontextandhorizons,andforthisreasonmaybebetterthoughtofasademographicapproximatetothefertilityandmortalitydynamicsofindustrialsocieties.Forjustassoonaswemovebeyondthesesocieties,whetherthisbebackwardstowardstheagriculturalone,orforwards
towardstheknowledge,information,(orwhatever-you-want)society,thetheorynolongerworksinthewayitshould,andcannolongerexplainwhat,inprinciple,itoughttobeabletoexplain.
Maybethen,inmovingbothbackwardsandforwardsintime,weshouldgoforthe'bigpicture'evenifthisimpliesassumingtheriskofwhatPeterMcDonaldhas-rathercritically-calledtakingthetheoryontoan'evergranderlevel'.Someworkhascertainlymovedinthisdirection.WilsonandAirey,inarguingforamuchmoregeneralised'homeostatic'versionofthe
theorymaketheveryreasonablepointthatthereisnowconsiderableevidencetoindicatethat,overthepasttwomillenia,therehavebeensubstantiallong-runchangesinratesofpopulationgrowth(WilsonandAirey1999).Astheysay,therehavebeenperiodsofsustainedpopulationgrowthfollowedbyperiodsofsustaineddecline.Dependingonwhereintimewesituateourselvesinthisprocess,wemaywellcometoviewtransitiontheoryverydifferentlytothewayinwhichNotestein,Davisetaldid.Oneresponsetothisrecognition,anditisinfactthepathwhichWilsonandAireychoosetotake,istoarguethatsuchfluctuationssuggestthatthereisaverylong-runprocessatwork,andthatonesuchpossibleprocessmightbe
homeostasis,asituationwhereby,wheneverpopulationandresourcesgetoutofbalance,mechanismscomeintoplaytorestorethatbalance(WilsonandAirey1999).Oneoftheprincipalmodernproponentsofthisviewhas,ofcourse,beentheItaliandemographerMassimoLivvi-Bacci(LivviBacci,2001).
AnothermodeloflongrunpopulationgrowthwouldbethatoriginallyoutlinedbyRonaldLeeinthe1980s(Lee,1987,1988)andsubsequentlytakenupbynumerouseconomistsworkingintheneo-classicalgrowthtradition(Kremer,1993,Lucas,2002HansenandPrescott,2002,Galor2005,GalorandWeil,2000).InthisaccountLeecombinestheMalthusianandtheBoserupian
(Boserup,1965)versionsofhistorytogenerateamodelwherehumanagentsareconstantlyforcedtogeneratenewtechnologyasthepressuresofincreasingpopulationpushagainstthelimitsofresourcesupply.Thisaccounthasthevirtueofsimplicity,andofprovidingaprettygoodfitwiththeevolutionofglobalpopulationforaperiodofabout10,000years(fromtheagricultutralrevolutiontothemiddleofthetwentiethcentury).Ithasthestrongdisadvantagethatnothingwithinthetheoryeitherpredicts,forseesorisabletoaccountforbelowreplacementfertility.Sothetheoryisfineasastatementofwhathashappened(alookingbackwardscapacity),butitdoesnotseemtodescribethepresentrealityofthedevelopedworld,anddoesnotseemtohavewhatLakatoswouldhaveconsideredanessentialfeaturefora
progressiveresearchprogramme:theabilitytopredictinterestingnewfacts(alookingforwardscapacity).
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Ofcourseinthehistoryofscienceithasbecomeatruismtostatethatwhatyouputinverymuchconditionswhatyougetbackout,andinparticular(followingBacon)thatthequestionswhichyouputtonatureverymuch
conditiontheanswerswhichsheoffersinreply.Demographictransitiontheoryisnoexceptionhere.Thekeyanalyticquestionwhichwasdeveloped(andbecame*the*highpriorityresearchissueontheagendaofthedemographicprofession)washowtoidentifythespecificsocietalchangeswhicharelikelytotriggerthedesiredreductionsinfertilityinhighfertilitysocieties.Simplyaskingthisquestionnaturallywastheprimummobileforanattempttoachieveamuchmorefocusedtheoreticalframeworkascomparedwiththeearlierfixationonclassifyingthetransitionbystages.Thiswasanimportantshiftsinceanswerstosuchquestionswouldnotonlybeoftheoreticalinterestbutcouldalsoguidepoliciesdirectedatfertilitydecline,andthiswasofcourse'thegrail'formanypractisingdemographers.
Researchinthesetermscontainedtwobasiccomponents:theconstructionofdetailedtimeseriesdataonfertilityandtheidentificationofappropriatedemographicandsocio-economicvariables,acrossavarietyofpopulations,tofacilitatetheestablishmentofaninformedpolicyframework.Thehighwatermarkoftheseambitionswas,ofcourse,theEuropeanFertilityProject(EFP),oneoftheearliest(andinitsdaycertainlyoneofthemostambitious)large-scaleresearchprojectseverundertakeninthesocialsciences.BasedinPrinceton,theprojectwasinauguratedin1963.Initiallytheobjectivewassimplytopresentasystematiccollectionofstatisticaldatadocumentingfertilityandrelatedsocio-economicchangesinseveralhundredprovincesof
Europeduringtheyearsofthemajorfertilitydecline.Theideaessentiallywasthatthedocumentationsoassembledwouldenablethetestingofclassicdemographictransitiontheory-thatis,thetestingoftheclaimedassociationsbetweenspecificmodernisationindicatorsandfertilitydecline.
Reallygiventhewaytheprojectwassetuptheoutcomewasprettymuchthechronicleofadeathforetold:theprojectteamconcluded(seeCoaleandWatkins,1986)thatthetimingoftheonsetofthefertilityreductionswasnotstronglylinkedtoanyidentifiableprovince-specificlevelsofsocio-economicmodernisationandindeedseemedtobemorestronglyassociatedwith
language,ethnicorreligiousdifferences.Inparticularresearchersfoundithardtoidentifyanystrongassociationbetweentheonsetofthefertilitytransitionandchangesintheeconomicvalueofchildren(KnodelandvandeWalle,1986).
Now,morerecentresearchbasedonGermanandotherdatahasbeguntocastdoubtonthegeneralisedvalidityoftheEFPfindings.Inparticulartheissueofthevalidityofusingaggregatedatainthewaytheydidhasbeenraised(Gallowayetal,1994,Brownetal,2002).Howeverthisisbesidethepoint.CoulditnotbethattheEFPwasmistakenastoitsobjectives?Andinprincipal.Mightitnotbethatwhatisneededfirstandforemostisamotor,and
ageneraltheoreticalmodelwhichcanexplainwhytheunderlyingchangesinfertilityoccur,whichcanexplainwhatdrivestheprocess?
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PeterMcDonaldhasarguedsomethingsimilar,namelythatempiricaltestingofdemographictransitiontheoryfocusedheavilyondiscoveringtheconditionswhichleadtotheonsetofthetransition,butgavemuchless
importancetoitsprogressionand,inparticular,toitsendstate(McDonald,2001).Casterline,ontheotherhand,hasconcludedthatconfrontedbythefindingsofthePrincetonproject,scholarsturnedtootherexplanationstoaugment,oreventosupplant,thedominanttheoreticalframeworkinwhichtheprimarycausalforcesunderlyingfertilitydeclineweremortalitydeclineandtheparadigmaticeconomicandsocialchangesthatoccurredinEuropeinthenineteenthandearlytwentiethcenturies(Casterline2001b,p.2).
Theprincipalalternativeswhichwereproposedhavebeenlooselycollectedunderthelabeldiffusiontheories.ThisterminologyowessomethingtosomeearlyworkbyCarlsson(Carlsson,1966)wherehedrewadistinction-
concerningtransitiononset-betweeninnovationanddiffusion,andsinceCarlssontransitionanalysishasnormallybeendividedbetweenthosetheorieswhichemphasisetheprocessofadjustment(oradaptation)tochangingsocioeconomicordemographiccircumstances,andthosewhichemphasisetheimportanceofthediffusionofinnovationeffects.Carlssonhimself,forexample,focusedonthediffusionofaninnovation,inthiscasetheuseofcontraceptionandabortion.Conceptualisationofthetransitionnowbecamefocusedonwhatwhatwasbeingtransmitted(theinnovation)andonhowitwasbeingtransmitted(thediffusionofinnovationamongindividualsandfamilies).AsClelandputit:
theengineofdemographicchangeisthestructuraltransformationofsocieties,anddiffusionisthelubricant(Cleland,2001,p.45).Puttingthisanotherway,AnsleyCoalefamouslydeclaredthatfertilityreductionswouldoccurwhencoupleswere"ready,willingandabletocontrolfamilysize"(Coale,1973).
Butthisisjustthepoint.Innovationtheoryexplainshowwomenwereabletocontrolfertility,diffusiontheoryexplainswhytheyarewillingtodoso,butwhichpartofthetheoryexplainswhytheyarereadysotodo?Takingthepointfurther,andbendingjustalittleCoale'soriginalstatementwecouldsaythatthefundamentalchallengefacingdemographictransitiontheoryisto
explainwhymodernwomeninhighlydevelopedeconomiesandsocietiesseem"*evenmore*ready,willingandabletocontrolfamilysizethantheyeverwerebefore".Fromaperfunctoryglanceatthegeneralisedavailablityofthemosteffectiveformsofbirthcontroltechnologyeverknowntomankindwecaneasilyappreciatethefactthatwomenarebetterabletocontroltheirfertilitythanever,andwecanseeinthecontextofthewidevarietyofsociologicalandideationalexplanationswhytheymightbeexceedinglywilling,butwhyisitthattheyaresoreadytodoso?Addingperhapsalittlemorecuttingedgetothisapproach,Oppenheimersuggestedthattheincreasingeducationofwomenraiseswomens
aspirationsregardingthequalificationstheyincreasinglyfind'essential'whendefiningtheirfutureidealspouse.This'upgrading'initselfprolongsthe
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searchinthemarriagemarketandthuspostponesmarriageorpartnershipformation,eventotheextentofprecludingitentirelyshouldtheappropriatepartnernotappear(Oppenheimer,1988).
BackToOurRootsBackToOurRootsBackToOurRootsBackToOurRoots
AsIsayabove,ratherthanbeginingafertilitytheorywitheventswhichoccurattheendoftheeighteenthcentury,togetanadequatehandleonmortalityandfertilitydynamicsperhapsitwouldmakemoresensetobeginouraccountsome10,000yearsearlier,withtheoriginsofsystematicagriculture.Thereare,inthefirstplace,goodtheoreticalargumentsfordoingthis,sincetheagriculturalrevolutionseemstohavemarkedwhatmanyevolutionary
biologists,anthropologistsandpsychologistsregardasbeingattheveryleastasignificantwatershedinourbiologicaladaptiveevolution,ifnottheterminationoftheeffectivebiologicaladaptiveprocessformodernhumans.Thereisalso,inthesecondplace,aclearempiricaljustificationforthischoice,sincethearrivalofagricultureclearlymarksthetransitionfromonefertilityregimetoanother.Systematicagricultureconstitutesabreakpointinanothersense:itmarksatransitioninthehumanreproductivecyclefromwhattheanthropologistHillardKaplantermsexclusivelysomaticformsofenergyaccumulation,toasystemofenergyaccumulationwhereinthereisacombinationofboth
somaticandnon-somaticforms(KaplanandGangestead,2004).Priortotheagriculturalrevolutionitispossibletoarguethat,viatheprocesseswhichhavecometobeknownas'naturalfertility'(Henry,1961),humanfertilitywashomeostaticallyregulated.Such'naturalfertility'waseffectivelycomprisedbyacombinationoffluctuatingfirst-birth-agesandchangesinthedistributionofbirths,andthesewereregulatedbyacombinationoftaboosandsocialpracticesandbychangesinnutritionandotherenvironmentalfactors.Thatsuchmechanismsexistinhumanpopulationsishardlysurprisingsincevirtuallyallcomplexorganismsexhibitsomesortofflexibilityinbothage-at-first-reproductionandfertilityrates.
Naturalselectionitseemshasresultedintheappearanceofphysiologicalandpsychologicalmechanismsbywhichbothorganismsandindividualsadjustfertilityonsetandfertilityratesinrelationtochangingenvironmentalconditions.Inthecaseofpre-agriculturalhunter-gatherersocietythisregulationseemstohavebeenachievedbymeansofavarietyofreproductivestrategies-suchas,forexample,extendedlactation,orfluctuatingageatmenarche-manyofwhichhavethecharacteristicofbeingbiologicalresponsestoaconstantlychangingexternalenvironment(Ellison,2001).Putinotherwordstheymaybedescribedas'naturescontraceptives'.
However,withtheadoptionofagriculturesomethingnewhappens,andthis
somethingnewmaybeconsideredtoformthevertebralcomponentofafromthenonongoingprocess,aprocesswhichhassubsequentlycontinued
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throughtheindustrialrevolution,andindeedcanbethoughtofascarryingstraighton,inonebroadsweep,intotheso-calledinformationsociety.
LifeHistoryTheoryLifeHistoryTheoryLifeHistoryTheoryLifeHistoryTheory
Accordingtothetheoryofevolutionbynaturalselection,theevolutionoflifeistheoutcomeofaprocessinwhichvariantformscompetetoharvestenergyfromanenvironmentandconverttheenergysoharvestedintoreplicatesoftheformsthemselves(Kaplanetal,2004,Kaplanetal2003).Theformswhicharemoreeffectiveincapturingenergyandinconvertingitmoreefficientlyintooffspringbecomemoreprevalentthroughtime.Thisprevalancecanalsobeconsideredasanexpressionofwhatbiologistscall'fitness'.Fertilitywhenviewedinthislightmaybethoughtofascontributingdirectlyto
fitness,andindeed,allotherfitnesscomponents,suchasmortality,maybeconsideredtoaffectfitnessonlythroughtheireffectsonfertility.Mortalityrates,forexample,affectfitnessbyaffectingtheprobabilityoflivingtothenextreproductiveevent.Thus,otherthingsbeingequal,anyincreaseinfertilityis,inandofitself,anincreaseinanorganism'sfitness.Howeverlifeisneverthatsimple.Twotrade-offshavebeenidentifiedwhichaffectthewayinwhichnaturalselectionactsonfertility.(Charnov1993,Lessells1991,Roff1992,Stearns1992)
a)Thefirstoftheseisthetrade-offbetweenpresentandfuturereproduction.Thecentralissuehereisgrowth.Bygrowing,anorganismcanincreaseitsenergy-capture-rateinthefutureandthusincreaseitsfuturefertility.Ontheotherhandearlyreproductionmaybethoughtofasfavouringfertilitybylengtheningthereproductivelife.Atthesametimetheearlyinitiationofreproductionshortensgenerationlength,andinthiswayincreasesthelineage.Thedecisionthereforeis:noworlater.b)Thesecondtrade-offistheonebetweenquantityandqualityofoffspring.Qualityhereisafunctionofparentalinvestmentinanoffspringandtheoutcomeofthisinvestmentisdirectlyreflectedinitsabilitytosurviveand
reproduce.NowtheresearchprogrammeknownasLifeHistoryTheorypostulatesthatanoptimallifehistorywouldchoseoffspringinvestmentandmortalityreductionjustsoastomaximisetotalexpectedsurplusenergyoverthelifecourse.Alsolifehistoriesmaybethoughtofasbeingcomposedbyspecialized,co-adaptedbundlesoffeaturesthatregulateageschedulesoffertilityandmortality,andrespondflexiblytolocalecology.Fromthisperspectivethehumanlifehistory,whichevolvedduringtheforagingniche,ischaracterised
bythefollowingfeatures:aninitiallearning-andbrain-intensivedevelopmentstagewherethereissubstantialandextensivedependencyon
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parentsandwhichisbothprolongedandresourcecostly,anextremelyproductiveadulthood,andalonglifespanwhichfacilitatesathreegenerationalsystemofresourceflowsinwhichgrandparentsaswellasparentsactivelyprovisionchildrenandadolescents.
Duringthethousandsofgenerationswhichpassedwhilehumansbecamegraduallyadaptedtotheskill-intensiveforagingniche,naturalselectionactedonhumanpsychologyinsuchawayastoleadhumanstobecomesensitivetoenvironmentalvariationinlearningopportunitiesandtotheirpayoffs.Asaresultofthiswearearguablywell-adaptedtoadjustbothourinvestmentsinown-learningandourinvestmentsinthedevelopmentofourchildreninresponsetosuchenvironmentalvariation.Nowwhenallwealtheithertakestheformoffoodenergydirectlyconsumedortheformof'crystalised'energy(acquiredknowledgetobefoundintheskillandcultureofthegroup),adirectlinkcanbeseenbetweenparental
investmentandtheenergeticsofreproduction.Thislinkismediated-adaptive(thatistosayfitness-maximizing),andincreasesanddecreasesfertilityinresponsetochangingpayoffstoparentalinvestment.Inthecontextofmoderneconomic,technological,andsocialconditions,however,thisevolvedpsychologyandreproductivephysiologymaybeconsideredtoproduceresponsesthatdonotmaximizefitnessasitisclassicallyunderstood.(Kaplanetal,2003).Theseresponsesdo,nevertheless,followtheirownlogic,andtryingtounderstandthislogicreallyconstitutestheprincipalchallengefacingacomprehensiveversionofdemographictransitiontheory.Infact,whenwecometotryandanalysesit,thereasonwhyourmodern
reproductiveresponsesdonotmaximisefitnessis,initself,interesting.Thekeypointtonoteisthatitwastheemergenceofextra-somaticwealth(i.e.,land,livestock,andotherformsofphysicalandtransferablecapital)co-extensivelywiththeevolutionofagriculturewhichlargelybroketheclassiclinkbetweenparentalinvestmentandtheenergeticsofreproduction.(Isaylargelybroke,sinceofcoursenobreakis,inandofitself,totallyabruptandcompleteone.Inbiologicaltheorywemightfindthisnotionincorporatedintheideaofredundancy,inthecontextofKaplan'senergetics,itmightwellbearguedthatthecrystalisedenergyofthepre-agriculturalepochwasnotnecessarilyasexclusivelyfitnessmaximisingashasbeensuggested.The
transitionfromcrystalisedenergyformedandcarriedaroundinthegroup,andnon-somaticenergystoredinabarnwasnotanovernightone,andtheprocessdoubtlesslastedformanygenerationsandformanythousandsofyears).However,fromthetimeofsystematicnon-somaticenergycreationonwardschangesinfertilitymaybeconsideredtobetheproductofacircular-causalityprocess,aprocessinwhichcontinuinginteractionwithacontinually-transformedandtransformingenvironment(whichisincreasinglyaninstitutionallymediatedone)produceschangesinbraintissue(changesthatisinthewaythebrain'frames'itsenvironment),changesintheideas-content
ofthethoughtprocess,andfinallychangesintheconstantlyevolvingtechnologyitself,changeswhich,in-their-turn,oncemoretransformthe
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environment,andsoon.Thevertebralaxisofthisprocessistime,andtheconstantlyincreasingnumberofyearsforwhichitisworthsubsidisingthepreparationofchildren.Thiscircularprocessisitselffacilitatedbyasub-systemwhichworksasfollows:increasinglycomplextechnologymeansincreasedlearninginvestmentinordertobeabletouseanddevelopit,but
applicationofthetechnologyitselfenhanceslifeexpectancywhichinturnmakestheinvestmentinincreasedchildhoodpreparationworthwhilesincetherearemore'peakadultyears'inwhichtoexploitthebenefitsetc.etcetc.etc.Duringtheindustrialsocietyyears,forexample,newtechnologiesalteredthedistributionofavailableemployment,increasingintheprocessthebenefitsofschoolingandthevalueofon-the-jobtrainingforbothmenandwomen.Inthesecondplacethesetechnologiesincreasedtherelativepayoffsofmarket-orientedascomparedwithhome-orientedlabourforwomen,inthiswayincreasingthe(opportunity)costsofchild-rearingand(asaside-effect)
decreasingmaritalstability.Atthesametimeanassociatedincreasedefficiencyinbirthcontroltechnologies(andinparticularthearrivalofthebirthpill,thatmostefficientofalltheefficienttechnologiesofcontraception),gavewomenmoredirectcontrolovertheirbodiesandoverthereproductiveprocessitself.Itisperhapsworthmentioningjustonefurtherexampleofsub-systemfeedbackeffectsonthisprocess:thedecliningstrenousnessofworkandthetechnologically-facilitatedpressureonthewaywomen'stimeisnowdistributedbetweenhomeandwork.IntheUnitedStatesavarietyofstudies,usingprincipallydatafromtheUSBureauofLaborStatisticsDictionaryof
OccupationalTitles,haverecentlyexaminedjobstrenuousnessratings(LakdawallaandPhilipson,2002;Cutleretal.,2003)insearchofinsightsintothecausesofthesteadyupwardtrendwhichhasbeenobservedinobesitybothintheUnitedStatesitselfandelsewhere.Ingeneralresearchershaveidentifiedaclearshiftawayfrommore-strenuousandmorestrength-demandingjobstowardslessstrenuousandlessstrength-demandingones,withthisshiftbeingevenmorepronouncedinthecaseoffemaleworkersthanithasbeenformaleones.TheshiftfromanagriculturaltoanindustrialeconomyandthentoaservicesonehasbeenemphasizedbyauthorssuchasPhilipson(2001)ineconomicanalysesofobesity,withattentionbeingdrawntothefactthatthistransitionhasbeenaccompaniedbyinnovations
thateconomiseontimepreviouslyallocatedtothenon-marketorhouseholdsector(intermsofthewidespreadadoptionofindustrialisedalternativesto'homecooking').Technologicalchangehasthusbothfacilitatedashiftinlabour-marketemphasisawayfromphysicallystrenuousjobsandtowardsanincreasedpressureonhome-timeatthesametimeasithasleadtotheintroductionoftheverytechnologywhichmakesthistimereductionpossible.EmbodiedCapitalEmbodiedCapitalEmbodiedCapitalEmbodiedCapital
Ashasbeensaidchildbirthpostponementformsacorepartofourinheritedfertilityregulatorymechanism,apartwhichhas(notcoincidentally)been
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revealinglycharacteristicofthemostrecentfertilitydeclineindevelopedsocieties.Inthispostponementprocesstwocentralfeaturesseemtostandout:1)Theever-increasedinvestmentsineducationandinplasticity(flexibility,
lifelongdevelopment)whichlabourmarketparticipationimposes.Theseinvestmentshaveperhapshadtheirmostnotableconsequencesintheirimpactonwomenandtheirreproductivebehaviour.2)Theincreaseinbothown-andoffspring-investmentshaspossiblyleadtogreaterselectivityonthepartoffemaleswhenidentifyingasuitablepartnerwithwhomtoco-investinchildren.Thisselectivityisontheonehandaresultofthecrucialroleofbothmaternalandpaternalskills-basedinvestmentsinthedevelopmentofoffspring,andtheunequaldistributionoftheseinvestmentsbetweenthesexes.Ontheotherhandthisselectivityisincreasinglyaproductofthechangingpatternsofpartnershipstabilitywhich
accompanythemodernlifecourse.
HillardKaplanhassuggestedthatonefruitfulwayoflookingatthiswholeprocessisviatheconceptof'embodiedcapital'alreadywell-knowninmacro-economicsforitsroleininvestmenttheoryandgrowthaccounding(Kaplan,2003).WhatKaplanproposesisthatthepresent/futurereproductiontrade-offmayperhapsbebestunderstoodintermsofoptimalinvestmentsinown-versusoffspring-embodiedcapitalwhichoccursthroughreproduction,andthatthequantity-qualitytrade-offcanitselfbeunderstoodintermsthesizeofofinvestmentsintheembodiedcapitalofoffspringvs.thenumberof
offspringproduced.Kaplanarguesthatembodiedcapitaltheoryallowsustoaddressproblemswhichstandardlifehistorymodelshadpreviouslybeenunabletohandle.Inthefirstplace,theexclusivefocusofclassiclifehistorytheoryonphysicalgrowthofferedonlyaratherpartialunderstandingofhumandevelopment.Thelargehumanbrain,forexample,embodiesastockofcapitalwhichincludesagreatdealofskillandknowledgeacquiredduringboththejuvenileandtheadultperiods.Inthissensegrowthintheformofknowledge(intensive,ratherthanextensivegrowth)maybejustasimportantasgrowthinbodyandbrainsizewhenconsideredwithrespecttotheprovisionof
benefitsthroughtime.Inthesecondplace,parentalinvestmentnotonlyaffectssurvivaltoadulthoodofoffspring,butalsotheadultincome(orproductivity)oftheoffspringproduced.Thisisjustastrueofhumansinmodernsocietiesasitwasamongstourancestorsthehunter-gatherers.Ashasbeensuggested,embodiedcapitalisaconceptwhichisfamiliartoeconomists,inparticularthisfamiliarityisduetoawell-knowndisputeingrowththeory,adisputewhichsubsequentlybecameknownasthe
'embodimentcontroversy'.Theembodimentcontroversyfamouslytookplaceinthe1960sbetweenthe'father'ofgrowthaccountingDaleJorgenson
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(Jorgenson,1966)andthe'grandfather'ofneo-classicalgrowththeoryRobertSolow(Solow(1960).ConvenientsummariesofthiscontroversymaybefoundinHulten(1992),Greenwoodetal(1997)andHercowitz(1998).Thedisputecenteredaroundtheimportancewhichshouldbeattributedto
capital-embodiedtechnologicalchange.Thereasoningbehindthecontroversygoesasfollows:iftechnologicalchangeisdisembodied,itaffectsoutputgrowthindependentlyofcapitalaccumulation,incontrast,embodiedtechnologicalchangerequiresinvestmentinordertoaffectoutput.Hence,determinationoftherelativeimportanceofthetwoformsoftechnologicalchangeiscrucialforunderstandingtheprecisetransmissionmechanismwhichexistsbetweentechnologicalprogressandoutputgrowth.Solowarguedthatembodiedtechnologicalchangeisthedominantpartner,andhence,investmentisthekeymechanism,whileJorgensonstressedtheimportanceofimprovementsinthe'quality'ofcapitalservicessupplied.
Tocontextualisethisalittle,economictheorysuggeststhattherearefourpossiblesourcesofproductivitygrowth:bettertrainedorbettereducatedworkers,betterwaysoforganizingproduction,moreinvestmentincapital(equipment,buildings,andsoforth),andlastly,improvedqualityofcapital,thatis,equipmentthatworksfasterorbetterinsomeway.Itisthislastsourcewhichhasbecomeknownintheliteratureastheembodiedtechnologicalchangecomponent.Duringtheinternetboomofthelate90s,forexample,manyobserversattributedmuchoftheproductivitysurgetoembodiedtechnicalchange.
Solowhimselfacknowledges(inhisNobelPrizelectureforexample,seeSolow,1987)thathisoriginalversionoftheneo-classicalgrowthmodelomittedtheembodimentmechanism,andthatthisabsencewouldclearlyleadtoabiasawayfromtheinvestmentprocessinthegrowthaccountingexerciseswhichwerecarriedoutusinghisinitialmodel.Solowlatermodifiedhisinitialgrowthmodel(Solow,1957),andinthenewversiontheeffectivenessofinnovationinincreasingoutputwasreflectedbytherateofgrossinvestment.Apolicytoincreaseinvestmentwouldthusleadnaturallynotonlytohighercapitalintensity,whichmightnotormightnotbeakeyfactor,butalsotothefastertransferofnewtechnologyintocurrentproduction,andthisobviouslywouldbe.
Theintriguingpointhereisthattheremaywellbeaparalleltobefoundbetweeninvestmentandembodimentinfixedcapitalandininvestmentinthehumanvariety,sincebraingrowthalsoembodiesimprovedhumanbrainquality.Oneoftheconsequencesoflookingatthingsthiswaymightbe,forexample,thatoneisthenabletoaskthefollowingquestion:whatproportionoftheincreaseinhumanperformanceoverthatofotherhigherprimatesisduetotheincreasesinhumanbrainsize(orgreaterenergeticinvestmentinitself)andwhatproportioncomesfromincreasedqualitywheretheimprovementsaredrivenbycontinuinginteractionwithanexternalenvironment?Inthelattercaseanincreasing-returnslearning-by-doing
elemententersthecalculations,sincethesamequantitiesofenergy-throughputarerecycledtoachieveahigherbrain-outputadvantage,andthis
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learning-by-doingbothimplicitlyaltersthemostfavourablefertilitytrade-offpath,together,conceivablywiththeendstatewhichisultimatelyachieved.Takingthisideaonestepfurther,itmightbenotedthatoneverythoughtprovokingsetofmodelswhichKaplanandhisco-workershaveproduced
triestoarguesomethingwhichimpliesjustthis:thatinvestmentsinembodiedcapitalaffectingadult-income,orratesofenergy-capture,shouldbeconsideredtoco-evolvewithinvestmentsaffectingmortalityandlongevity(Kaplan,1996;Kaplanetal.,2000;KaplanandRobson,2001).Hencethelongerthetimespentgrowingandlearningpriortoreproducing,themorenaturalselectionisgoingtofavourinvestmentsinstayingalivetoreaptheaccumulatedbenefits(thehigherratesofreturnfromskills-basedproductivity)ofthoseinvestments.Similarly,anyinvestmentsthatproduceincreasedenergy-capture-ratesinmiddle-ageinherentlyselectforthedesireabilityofadditionalinvestmentstoreachtheolderages.Soitcanbe
seenthatecologicalfeaturesorinvestmentsthatincreasetheprobabilityofsurvivaltoolderagesalsoproduceselectionforgreaterinvestmentsinincome-relatedembodiedcapital.Itisnotdifficulttoarguethatsuchco-evolutionaryeffectshavebeenparticularlyimportantintheirconsequencesforhumanlifehistoryevolution.
NotunsurprisinglyallofthisfitsextraordinarilywellwiththekindofworkthatJamesVaupelandothersaredoing(Vaupel,2004).ForagingToAgricultureForagingToAgricultureForagingToAgricultureForagingToAgriculture
Soifthecourseofactionbeingadvocatedhereisthatofrollingbacktheclock10,000years,thenitisobviouslyimportanttoaskourselvesjustwhatempiricalevidencethereactuallyisthatthechangefromforagingtoagriculturewasoneawayfromfitness-driven'naturalfertility'toafertilityregimewhichwasassociatedwithaquitedifferenttypeofmechanics.Well,studiesofthefertilitytransitionfromforagingtoagriculturehavecertainlytendedtofindthat(cry'sofshame,shamefromtheCaldwellsnotwithstanding:seeCaldwellandCaldwell,2003)onbalance,fertilityinintensiveagricultureismarginallyhigherthanitisinforagingsocieties
(KramerandBoone,2002).KramerandBoonebasetheirevaluationonavarietyofpriorstudies(CampbellandWood,1988,Hewlett,1991,Bentley,Jasienska,andGoldberg1993,Bentley,Goldberg,andJasienska1993).IndeedCampbellandWoodelaborateacross-culturaltabulationoftotalfertilityrates(TFRs)for70forager,horticultural,andintensiveagriculturalsocietiesbasingthemselvesonthecontemporaryethnographicrecord.TheirfindingsshowthatthereisverylittlesignificantdifferenceinTFRsacrosssubsistenceregimes.Hewlettcarriedoutasimilaranalysisof40mobileandsedentaryforagersandpastoralists.Hefoundtheexistenceofslightlyhigherfertilityratesamongpastoralists,althoughthedifferencewasnotsignificant.
Bentleyetal.subsequentlypublishedanextensivecritiqueandre-evaluation
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oftheCampbellandWoodstudy,presentingtheirowncross-culturalcomparisonof57forager,horticultural,andintensiveagriculturalgroups.UsingasubsetoftheCampbellandWoodsample,excludingnon-independentcases(ethnicgroupsthatwerecloselyrelated)andpopulationswithhighlevelsofsterility,theyfoundthatintensiveagriculturalistshad
significantlyhigherfertilityrates.Withinthesample,however,horticulturalistsshowedslightlylowerfertilitythanforagers,althoughthedifferencewasnotsignificant.Thislatter'horticulturalistanomaly'leadsKremerandBoothtoconcludethat:"IfsedentismortheavailabilityofagriculturalfoodsisindeedadecisivefactoraffectingTFRsacrosssubsistenceregimes,wewouldexpecthorticulturetobeaclearlandmarkinfertilityincrease.Thatnoneofthesestudiesfounditsosuggeststhatthedevelopmentofagricultureorsedentismpersedoesnotaccountfortheincreaseinfertility.YetfurtherexplanationisneededifintensiveagriculturalistshaveasignificantlyhighermeanTFRandarethe
onlygroupsrepresentedintheupperrangeofthefamily-sizecontinuum."EssentiallytheanswerthatKremerandBoothproposeasasolutiontothisconundrumis,initeslf,significant,namely:thatthechild'scontributiontounderwritingthecostoflargefamiliesmaybethekeyfactorconditioningvariationinfamilysizeanddrivingtherelativelyhigherfertilityattainedinatleastsomeintensiveagriculturalsettings.Thisleadsdirectlyontoaveryinterestingquestion:coulditbethatthemodernideaoftechnologicalskill-bias(Galor,2005)mayhelpunderstandthepost-foragingfertilityevolution?Essentially,theskillcontentofalotof
agriculturalworkcouldbeconsideredtobeextremelylow(indeedlowerinsomecasesthanthatrequiredfortherelativelymoreskilledbig-gamehunting)andhencethelevelof'nurture'requiredbeforemeanifulproductiveactivitycouldbeundertakenwaspossiblyequallylow(indeedpossiblyevenlowerthaninthemoreskilledtypesofhunting)andthespacebetweenbirthswouldconsequentlybelower.NowallthisfitsinsurprisinglywellwithaclassofeconomicmodelswhichwasreallyinitiatedwithapieceofworkbyMichaelKremer(Kremer,1993).Kremerarguesthatpopulationgrowthandtechnicalchangeareintimatelyconnected.Hebaseshisargumentontheincreasingreturnspropertyof
ideas,whichexistduetothenon-rivalrycharacteristicsoftechnologyandthefactthatthenumberofideasproducedcanbeconsideredtobeafunctionofthenumberofpeoplethinking.Essentiallythecostofinventinganewtechnologyisindependentofthenumberofpeoplewhouseit.Thelongrunrelationbetweenpopulationgrowthandtechnologicalchangemaythusbeconsideredasstructurallysimilartotherelationbetweenideas,researchandgrowthwhichhasbeenmodelledintheendogenoustechnicalchangeliterature.(Erroneously,Kremerconcludesthattherateofpopulationgrowthisproportionaltothesizeofthepopulation,butthisisnotthepartofhistheorywhichisofinteresthere).Kremerarguesthatthealthoughtheoutputofeachindividualmaywellbeindependentofpopulationsize,totalresearch
outputshouldbeexpectedtoriseaspopulationincreasesduetothenon-rivalrypropertyofideas.(Thiscouldbecalledthe'more-Mozarts'effect.)
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Anumberofwellknowneconomistshadinfactpreviouslyworkedwithsomeversionofthisidea(Kuznets,1960,Lee,1983,Simon,1977).SubsequentlyKremer'scoreideawastaken-upbyBerkeleyeconomistCharlesJonesinaseriesofpapers(Jones,2001)aswellasbyHansenandPrescott(2002),
andRobertLucas(2002).Althoughthisentirelineofworkhasclearlimitationsinsofarasitdoesn'tinanywayenvisageasituationwherefertilitydropsbelowmortality,itishighlyrelevantinthesensethatittriestotietogetherpopulationgrowthandgrowthinideas.
KremerandBooth'sproposedconnundrumsolutionalsohasanotherinterestingresonance.WolfgangLutzandSergeiScherbovhaverecentlyengagedinsomeprobabilisticpopulationforecastingfocusedonIndia(LutzandScerbov,2004).LutzandScherbovbasedtheirworkonanexercisecarriedoutundertheauspiciesoftwoworkshopsorganisedbytheAsianMetaCentreforPopulationandSustainableDevelopmentAnalysisin2001
and2002.TheseworkshopswereorganisedwiththeobjectiveoftryingtoidentifythemaindriversofdemographicchangeinAsia.Aspartoftheexerciseaconsiderablenumberofin-depthinterviewswithwereconductedwithindividualexpertsinanattempttoascertainwhichstructuraldeterminantwouldbesingledout,usingassumptionsanalysistechniquesandconfidenceindices,asbeingthemostimportantoneindrivingfertilitychange.Thedeterminantso-identifiedwas,perhaps,hardlyasurprisingone:femaleeducation.
Thisfindingisentirelyharmoniouswitharesearchtraditionwhichcanbefoundontheothersideoftheplanet:intheeconomicsdepartmentof
ChicagoUniversity.MattiasDoepke,inapath-breakingandmostinterestingdoctoralthesis(Doepke,2000)-athesiswhichwassupervisedbyacommitteecomposedofRobertLucas,GaryBecker,EdwardPrescott,andRobertTownsend(amongothers)-cametowhatbynowshouldbeaprettyunstartlingconclusion,namely:thatthespeedofthefertilitytransitiondependsonpoliciesthataffecttheopportunitycostofeducation,namelyeducationsubsidiesandchild-laborrestrictions.Doepkeconsideredthecaseoftwocountriesthatstartedtogrowatroughlythesametime,butwhichhadexperiencedverydifferentgovernmentpolicies:(South)KoreaandBrazil.Koreahadastrongpubliceducationsystem,andchild-laborrestrictionswerestrictlyenforced,whileBrazilhadanineffectivepubliceducationsystem,with
littlesystematicenforcementofchild-laborrestrictions.Doepkefound,ashismodelpredicted,thatthefertilitydeclineassociatedwithdevelopmentproceededmuchfasterinKoreathaninBrazil.
InaseparatepieceofworkDoepkecomparesthepredictionsofthreevariantsofthealtruisticparentmodelofBarroandBeckerfortherelationshipbetweenchildmortalityandfertilityandfinds,quitecoherentlywithhisearlierwork,thatfactorsotherthandeclininginfantandchildmortalityareresponsibleforthelargedeclineinnetreproductionratesobservedinindustrializedcountriesoverthelastcentury(Doepke,2005).
Followingthislineofthought,andreturningtoKaplanforamoment,oneoftheinterestingarguementshemakesisthatstandardlifehistorymodels
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"tendtotreatinvestmentinthefutureasphysicalgrowth.Butgrowthisonlyoneformofsuchinvestment,asillustratedbybraindevelopment.Thebrainhasthecapacitytotransformpresentexperiencesintofutureperformance.Brainexpansionamonghigherprimatesrepresentsanincreasedinvestment
inthiscapacity.Butthisinvestmentisrealizednotonlyingrowthofneuraltissue;substantialenergyandtimemaybeallocatedtoencounteringexperiencesthat,throughchangesinneuraltissue,yieldbenefitsrealizedovertimeinvestmentsinthefuture."Sowhatif,atthebrain-sizelevel,apartfromevolvingforthegrowthandsustenanceofalargebrainwewerealsoatthesametimecontinuallytradingquantityforquality,whatif,asKaplansuggests,thebigdealinthecaseofmodernhumansisnotthenumberofourbraincellsbuttheirquality?Physicalgrowthisonlyoneformofbraininvestment.Ontheonehandneural
tissuemonitorstheorgan'sinternalenvironmentandinducesphysiologicalandbehaviouralresponsestostimuli(Jerison1973,1976),andontheotherhandthebrainhasthecapacitytotransformpresentexperienceintofutureperformance.Thislatterpropertyisparticularlyapplicabletothecerebralcortex,whichspecialisesinthestorage,retrievalandprocessingofexperiences.Theexpansionofthecerebralcortexamonghigherprimatesrepresentsanincreasedinvestmentinjustthiscapacity(ArmstrongandFalk1982,Fleagle1999,ParkerandMcKinney1999).Amonghumans,thebrainsupportslearningandknowledgeaquisitionduringthejuvenileandadultperiodswellafterthebrainhasreacheditsadultmass.Thegrowthinthestockofknowledgeandfunctionalabilitiesisanotherformofinvestment.
Toputallthisinsomeperspective,itisperhapsworthnotingthatithasbeenestimatedthatabout65%ofallrestingenergeticexpenditureisusedtomaintainthegrowthandsupportofthebrainduringthefirstyearoflife.(Holliday1978).Inanichewherethereislittletolearn,alargebrainmayhavegreatercostsinearlylifeandarelativelysmallinfluenceonproductivityinlaterlife.Ontheotherhandamorecomplexnicheundoubtedlyfavoursalargerbrain.Thebrainisnottheonlyhumansystemthatlearnsandbecomemorefunctionalthroughtime.Anotherexampleofsuchasystem(onewhich
requiresexposuretoanenvironment-inthiscaseantigens)istheimmunesystem.Itseemstobeagoodworkinghypothesisthatthematurationofourimmunesystemisoneoftheprincipalexplanationsforthedeclineinmortalitywhichoccurswiththeentryintoadolesence..Allofthisleadsusto,andfitsinsurprisingly-wellwith,somerecentworkbytheAmericanphilosopherandevolutionarypsychologistDavidBuller.InarecentbookBullerexaminesclaimsmadebyevolutionarypsychologiststhathumannaturewaseffectivelydefinitivelydesignedbynaturalselectioninthePleistoceneepoch(Buller,2005).BullerexaminesthisviewindetailandarguesthatthestrictEvolutionaryPsychologyversionofthestoryis
inadequate,atleastincertainimportantrespects.BullerconvinvcinglyarguesthatourmindsarenotadaptedindeterministicfashiontothePleistoceneera,
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but,likeourimmunesystem,arecontinuallyadapting,overbothevolutionarytimeandacrossindividuallifetimes.Bullerarguesthatevolutionisaprocess,notaframeworkdrivenbynaturalselectiontoarriveatfinishedproducts.HearguesthatHomoSapiensandall
indeedalllivingspeciesare"individuals"(spacio-temporallylocalized,continuousandcohesive)andnot"naturalkinds"(definedbyanessentialcharacteristic),thathumanpsychologicalmechanismsarehomologies(unifiedbycommondescent)anddonotfollowsimplelawsofnaturethatpertainexclusivelytothehumanmind(althoughtheydofollowlawsthatpertaintoallevolvedminds).Hesuggeststhatthehumanuniversalsthatweobservetodayarenotnecessarilyevidenceofphysiologicaluniversalsevolvedasadaptationswhenhumanswerehunter-gatherers,butaretheproductofaprocesswherebydevelopmentallyplastichumanbrainshaveevolvedspecificresponsestorecurrentenvironmentaldemands.
OneofBullersmainobjectivesistocounterargumentswhichhavebeenrecentlybeenadvancedbyanumberofprominentpsychologists(SeeCosmidesandTooby,1994forexample)insupportofwhathasbeencometobeknownas"themassivemodularityhypothesis"(Buller,2005).Thishypothesiswouldseemtohavetheconsequenceofgivingaheavyweightingtobiologicalevolutionintheexplanationofourcurrentbehaviour,sinceitadoptswhatappearstobethestrongestpossiblepositioninthisregard:thatthemindconsistsonlyofdomainspecificmentalmodules.Thesedomainspecificadaptationsareheldtobebiologicaladaptationsandareallegedtogivehumanbeingsaformofdomainspecificrationality,onewhichdispenseswiththeneedforanydomain-generallearning,orevenreasoning,
processes,evenifthesebeformalorlogicalones.Fodor(1983)wasperhapsthefirstinfluentialmodernthinkertoarguethattherearementalmodulesdedicatedtoperipheralandlowlevelinputandoutputcomputations.ButonFodor'saccounttheinputmodulespassinformation,bottom-up,toacentralprocessorforhigher-levelactivities,suchaslogicalorcontent-independentinference,whichcanthenin-turnhaveanimpactonoutput,top-down.DavidOverhasdescribedthemassivemodularityhypothesisasimplyingthatthemindislikeahugeswissarmyknife,withmanydedicatedblades,forsolvingadaptiveproblems,butnogeneralpurposetoolatitscentre(Over,2003).AsOverindicates,themost
seriousargumentforthemassivemodularityhypothesiswasfirstadvanced,manyyearsbeforethemodernevolutionarypsychologistspresentedit(eventhoughtheevolutionarypsychologistsseemunawareoftheprecedent),byKant(seeKant1987/1795).Inreality,Kantendorsedtheprincipalthattherecanbenoinstrumentforanypurposeinan'organisedbeing'whichisnot'bestadaptedtoit'.Kantgoesontoarguethatthepurposeofreasoninanycreaturecannotbetheinstrumentaloneofits'preservation','welfare',or'happiness',sinceinthatcase"naturewouldhavehituponaverybadarrangementinselectingthereasonofthecreaturetocarryoutthispurpose,foralltheactionsofthe
creatureforthispurpose.......wouldbemarkedoutforitfarmoreaccuratelybyinstinct,andthatendwouldtherebyhavebeenattainedmuchmoresurely
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thanitevercanbebyreason."(Kant1997/1785,395).Overgoesontosuggest,however,thatthereisonecrucialdifferencebetweenKantandthemodernevolutionarypsychologist,sinceKantconcludedfromhisversionoftheargumentthatasaconsequencereason
cannothaveaninstrumentalfunction,butratherexiststobeuseda-prioritoinfernormativelawsforallfiniterationalbeings.Kant(1981/1979)heldforexample,thatthereisanormativelawofreasonwhichrequiresustobehonest.UnlikeKant,evolutionarypsychologistsinferthatcontent-independentreasoningdoesnotexistatallandthatreasoningandrationalityaredistributedindomain-specifmodules,whicheventheysometimescallinstincts.OverthinksthatabetterinstrumentalistresponsetoKantwouldbethatformalorcontent-independentreasoningdoeshaveaninstrumentalfunction-that,withtherightpremisses,itcanbeofhelpinachievingpracticalgoals,by
supplementing,orevenbycompensatingforthedeficienciesofinstinctsordomain-specificmodules.Whatdoesallthismean?Well,essentially,andfollowingBuller(andotherslikeJerryFodor,seeFodor,1983),thefactthatadaptivebiologicalevolutionhasn'tchangedourbrainstoomuchinthelast10,000yearsisn'treallythebigdealinourevolutionaryhistorythatsomeseemtowanttomakeitouttobe,sincewhatisthebigdealisthechange(andnotthegrowth)inourneuraltissue.Thisiswhatthewholecontemporary'flexibilisation'debateisallabout,ourbrains'reconfiguring'(orwhatevermetaphoryouwanttouse)inthefaceofaconstantlyvaryingenvironment.
Bullerputsitlikethis:"This(theEvolutionaryPsychologyEH)pictureofthemindrunsafoulofcurrentknowledgeofbraindevelopment.......thebrainstructuresthatperformspecializedfunctionsdevelopthroughaprocessofdiffuseproliferationofbraincellsandconnectionsfollowedbya"pruning"thatshapesthisdiffuseconnectivityintorelativelyspecializedstructures(Deacon1997;Elmanetal.1996).Thatis,brainstructuresaretheproductofaprocessconsistingofboth"additive"events(theformationandmigrationofbraincellsandtheformationofneuralconnections)and"subtractive"events
(thepruningofsynapsesthroughcelldeathandaxonalretraction)(Elmanetal.1996).Inthisprocess,gene-directedproteinsynthesisisinvolvedintheadditiveeventsthatbuildthediffuseconnectivitywithwhichbraindevelopmentbegins.Thesubtractiveevents,however,arenotundergeneticcontrol.Rather,thesubtractiveeventsoccurthroughcellcompetition,wherebycellswiththestrongestpatternsofinnervation(primarilyfromsensoryinputs)retaintheirconnectionsandtheothersdie.Thus,genescodefortheproteinsinvolvedintheadditiveeventsduringbraindevelopment,buttheformsandfunctionsofbrainstructuresarethendeterminedbybraincell/environmentinteraction.Sothespecializedbrainstructureswehaveareprimarilyenvironmentallyinduced,not"geneticallyspecified."
"ButcontrarytotheEvolutionaryPsychologists'a-prioriargument,distinct
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"geneticallyspecified"moduleswerenotrequiredtosolvetheserecurrentadaptiveproblems.Ourbrainshituponadifferentsolution:generalplasticitythatallowsparticularenvironmentaldemandstoparticipateheavilyintailoringtheresponsestothoseverydemands.Thisprocesscanproducerelativelystablebrainstructuresthatspecializeprimarilyinparticularinformation-
processingtasks(thatis,somethinglikemodulescanemergefromthisprocess),andthesestructurescanbeproducedwithsomeregularityacrosspopulationsanddownlineages.But,theextenttowhichmodularizedoutcomesofhumanbraindevelopmenthavebeenregularthroughoutsomeofourevolutionaryhistoryisduetothefactthatdevelopmentallyplastichumanbrainshaveencounteredrecurrentenvironmentaldemandsthroughoutthathistory,notto"geneticspecification"oftheoutcomes."Attheendofthedaywhatdowehavehere?Well,asKaplanargues,inacertainsensehumangrowthanddevelopmentcanbeseenasanenergyharvestingprocess.Uptoacertainmomentinourhistorythisprocesscould
beseenasbeingaboutmaximisingfitnessinthetraditionalreproductivevaluesenseoftheidea.However,thearrivalofnon-somaticwealthaccumulationasanenergystoragesystemmodifiedthisprocess.Thistransitionseemstohavecoincidedwiththeterminationofalargeperiodofevolutionaryadaptationofthehumanbrain,andinparticularwiththeendofaperiodofrapidgrowthinthecerebralcortexwhichseemstohaveopenedthedoorforatransitionfromextensivetointensivegrowth,or,ifyouprefer,fromrelianceoncellquantitytorelianceoncellquality.Thisdoublemove,fromquantitytoqualityandfromsomatictoextra-somatic
seemstohaveopenedupalong-termprocessofideasdevelopment,wherethepay-backfromever-longerperiodsofinvestmentinoffspringqualityhassteadilyincreased,leadingtoanongoingprocessoflife-spanincreaseandfertilitydecline.Thisprocessofcoursecontinuesanditseemswillcontinuetocontinue.Thisiswhyweneedanewgeneraltheoryofthetransition.ReferencesReferencesReferencesReferencesAries,P.(1980).Twosuccessivemotivationsforthedecliningbirthrateinthe
West,PopulationandDevelopmentReview,vol.6,No.4,pp.645-650.Armstrong,E.,Falk,D.(Eds.)(1982).Primatebrainevolution.NewYork:PlenumPress.Austad,S.1999.WhyWeAge:WhatScienceIsDiscoveringabouttheBody'sJourneyThroughLife.NewYork:JohnWiley.Beckers,GaryS.(1981).ATreatiseontheFamily.Cambridge,Massachussetts:HarvardUniversityPress.
Bentley,gillian,g.Jasienska,andt.Goldberg.1993.Isthefertilityofagriculturalistshigherthanthatofnonagriculturalists?currentanthropology
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