Rethinking the Demographic Transition

8/2/2019 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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34:77885.Bentley,gillian,t.Goldberg,andg.Jasienska.1993.Thefertilityofagriculturalandnon-agriculturalsocieties.PopulationStudies47:26981.

Blake,Judith.1968.AreBabiesConsumerDurables?ACritiqueoftheEconomicTheoryofReproductiveMotivation,PopulationStudies22Bogin,B.A.,Smith,B.H.1996.Evolutionofthehumanlifecycle.AmericanJournalofHumanBiology8:703-716.Boserup,Ester.1965.TheconditionsofAgriculturalProgress.Chicago,Il.AldinePublishingCompanyBlurtonJones,N.B.,K.Hawkes,andJ.O'Connell(2002)Theantiquityofpost-reproductivelife:Aretheremodernimpactsonhunter-gathererpost-

reproductivelifespans?HumanBiology14:184-205.Bongaarts,John,andSusanC.Watkins(1996).Socialinteractionsandcontemporaryfertilitytransitions.PopulationandDevelopmentReview,vol.22,No.4,pp.639-682Brown,JohnC.andTimothyW.Guinnane,2002.FertilityTransitioninaRuralCatholicPopulation:Bavaria1880-910PopulationStudies,56,2002,pp.35-50,Bulatao,RodolfoA.,andJohnB.Casterline,eds.(2001).GlobalFertility

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Rethinking the Demographic Transition

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