The Demographic Transition: Three Centuries of Fundamental Change
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Journalof Economic Perspectives—Volume 17,Number 4—Fall 2003—Pages 167– 190 TheDemographic Transition: Three Centuriesof Fundamental Change Ronald Lee eforethe start of the demographic transition, lifewas short, birthswere many, growthwas slowand thepopulation was young. Duringthe transi- Btion, rstmortality and then fertilitydeclined, causing population growth rates rstto accelerate and then toslow again, movingtoward low fertility, long life and an oldpopulation. Thetransition began around 1800with declining mortality inEurope. It has now spread toall parts ofthe world and isprojected to be completedby 2100. This globaldemographic transition has broughtmomentous changes, reshapingthe economic and demographiclife cycles of individuals and restructuringpopulations. Since1800, global population sizehas alreadyincreased bya factorof six and by2100 will have risenby afactorof ten. Therewill then be 50times as many elderly,but only vetimes as many children;thus, theratio of eldersto children will have risenby a factorof ten. Thelength of life, which has alreadymore than doubled, willhave tripled,while births per woman willhave dropped fromsix to two. In 1800,women spent about 70percent of their adult yearsbearing and rearingyoung children,but that fractionhas decreasedin many parts ofthe world to only about 14percent, due to lowerfertility and longerlife. 1 Thesechanges aresketched in Table 1. Thesetrends raise many questions and controversies.Did population growso 1 With e(0) 5 27.5, Iassumethat womencared for young children from ages 20 to 50, sothat the fraction of adult lifespent givingcare is de ned in terms of lifetable functions as ( T(20) – T(50))/T20 5 71percent, where T(x)isthe survivalweighted number of personyears lived above age x. With e(0) 5 77.5, Iassumewomen care for young children from ages 25 to 33, sothat the fraction ofadult lifespent givingcare is ( T(25) – T(33))/T(20) 5 14 percent. y RonaldLee isProfessorof Demography andEconomics, University of California,Berkeley, California.His e-mail addressis ^[email protected] &. 168Journal of Economic Perspectives Table 1 GlobalPopulation Trends Over the Transition: Estimates, Guesstimates and Forecasts,1700 –2100 LifeExpectancy TotalFertility Rate Pop Size PopGrowth Rate Pop , 15 Pop . 65 (Yearsat Birth) (Birthsper Woman) (Billions) (%/Year) (%ofTotal Pop) (%ofTotal Pop) 1700 27 6.0 .68 0.50 36 4 1800 27 6.0 .98 0.51 36 4 1900 30 5.2 1.65 0.56 35 4 1950 47 5.0 2.52 1.80 34 5 2000 65 2.7 6.07 1.22 30 7 2050 74 2.0 8.92 0.33 20 16 2100 81 2.0 9.46 0.04 18 21 Source: Populationnumbers and growthrates for1700 are taken fromBiraben (1980) and for1800 from United Nations (1999). The guresfor TFR and e(0) arebest guesses by the author, consistent with the populationgrowth rate based on Coale-Demeny (1983) ModelSouth Female stable populations with an averageage of childbearingof 31and shouldnot betreated as data. The gureson agedistribution are likewisebased on these model stable populations. Data for1900 are from Chamie (2001), for1950 –2050 fromUnited Nations (2003) and for2100 from United Nations (2000). slowlybefore 1800 because itwas keptin equilibrium by Malthusian forces?Did mortalitybegin to decline because ofmedicalprogress, because ofrising per capita incomeor for some other reason? Did fertility begin to fall because ofimproved contraceptivetechnology and familyplanning programs,or were couples optimiz- ingtheir fertility all along and reducedit in response to changing economic incentives?Are we approaching abiologicallimit to life expectancy, or can we expectto see continuing oreven accelerating longevity gains? Some predictions suggestthat globalfertility is projected to fall to 2.0 children per woman, but in Europeit has beenonly 1.4 for some time, and ineastAsia itis 1.8; why should we expectfertility decline to stop at 2.0?Low fertility and increasinglongevity cause a dramaticchange inthepopulation agedistribution, with a ten-foldincrease in the ratioof elderlyto children.Will the societal costs ofthe elderly be catastrophic? In thepast, therehas beengreat concern that rapidpopulation growthin third-world countrieswould prevent economic development, but mosteconomists have down- playedthese fears. Similarly, environmentalists fear that worldpopulation isalready abovethe carrying capacity ofthe biosphere, while most economists are compla- centabout theprojected 50 percent increase in population overthis century.In this paper, Iwilldescribe these demographic changes ingreaterdetail, and Iwillalso touch on thesequestions and controversies. Before the Demographic Transition Accordingto a famous essay byThomas Malthus, rstpublished in 1798, slow population growthwas no accident. Population was heldin equilibrium with the RonaldLee 169 slowlygrowing economy. Fasterpopulation growthwould depress wages, causing mortalityto risedue to famine, war or disease —inshort, misery.Malthus calledthis mortalityresponse the “positive” check. Depressedwages would also cause post- ponementof marriage, resulting in prostitution and othervices, including contra- ception; this hecalled the “preventive” check. Sincepopulation could potentially growmore rapidly than theeconomy, itwas always heldin check by miseryand vice, which weretherefore the inevitable human lot.Economic progress could helponly temporarilysince population could soon growto its new equilibrium level, where miseryand vicewould again hold itin check. Only through moralrestraint —that is, thechaste postponement ofmarriage —did Malthus believethat humanity might avoidthis fate,and hethought this an unlikelyoutcome. Forpreindustrial Europe at least,Malthus seemsto have beenright. Popula- tionwas heldweakly in equilibrium by the positive and preventivechecks. When weather,disease or political disturbance knockedpopulation out ofequilibrium, realwages and rentsreacted strongly (Lee, 1987, 1997; Lee and Anderson, 2002), and thechecks broughtpopulation slowlyback toequilibrium. In westernEurope in the centuries before 1800, marriage required the re- sources toestablishand maintain aseparatehousehold, so ageat rstmarriage for womenwas late,averaging around 25years,and asubstantial share ofwomen never married(Flinn, 1981,p. 84;Livi-Bacci, 2000, pp. 99 –107).Although fertilitywas high withinmarriage, the total fertility rate (TFR) was moderateoverall at fourto vebirths per woman (Livi-Bacci,2000, p. 136).Mortality was also moderatelyhigh, withlife expectancy at birthbetween 25 and 35years (Flinn, 1981,pp. 92 –101; Livi-Bacci,2000, pp. 61 –90),2 but this was heavilyin uenced byhigh mortalityin infancy and childhood. Population growthrates were generally low, averaging 0.3percent/ yearbefore 1700 in western Europe, but sometimesrising above 1percentin the nineteenth century. 3 In Canada and theUnited States, marriage was much earlierbecause land was abundant, and population at rstgrew rapidly, but then deceleratedin the nineteenth century. Outside ofEuropeand itsoffshoots, fertilityand mortalitywere higher in the pretransitionalperiod, and change infertility and mortalitycame later. Data on mortalityor fertility are only occasionally availablefor third-world countries before WorldWar II(Preston, 1980).In India inthe late nineteenth century, life expec- tancy averagedin thelow 20s and was highlyvariable, while fertility was sixor seven 2 TheTotal FertilityRate isthe sumacross all ages of the birthrates at eachage and, therefore,measures the total numberof birthsa survivingwoman would have overher reproductive life, either actually for agenerationof womenor hypotheticallyfor a givencalendar year, whichis the morecommon usage. Lifeexpectancy at birthis the averageage at death foran actual generationor hypothetically the average ageat death impliedby the age-speci cdeath rates ina givencalendar year, whichis the morecommon usage. 3 Apopulationwith aTotal FertilityRate of4.5 and lifeexpectancy at birthof 30growsat 0.5 percent peryear (based on Coale-Demeny, 1983, stable population models with ameanage of childbearingof 31). 170Journal of Economic Perspectives birthsper woman (Bhat, 1989).In Taiwan, thepicture was similararound 1900. Widespreaddata on fertilityfor the decades afterWorld War IIcon rmthat total fertilityrates in the third world were typically six or higher. However, recent work suggeststhat thedemographic situation inChina mayhave beencloser to the Europeanexperience than previouslythought (Leeand Feng,1999). Although pretransitionalfertility was typicallyhigh inthird-worldcountries, its levelswere far below the hypothetical biological upper limit for a population (as opposed toan individual),which isaround 15to 17 birthsper woman (Bongaarts, 1978).The contraceptive effects of prolonged breastfeeding, often combined with taboos onsexwhile breastfeeding, led to long birth intervals and reducedfertility. Abortionwas also important, and sometimesthe practice of coitus interruptushad an importanteffect. In somesettings, marriage patterns also limitedfertility, although not as stronglyas inwestern Europe. Attheaggregate level, population growththroughout theregions of theworld was slowover the past millennium,but therewas apuzzlingsimilarity in longswings about thegrowth path, such as stagnation inthe fourteenth and seventeenth centuriesand morerapid growth in the fteenthand eighteenthcenturies. While exchangesof disease through explorationand trademay have playedsome role, globalclimatic change was probablythe main drivingforce (Galloway, 1986). Mortality Declines, Fertility Declines and Population