218. In actual fact, hlstorlcal mrtality declines have not been neutral. Mortality has generally declined in absolute terms more atlDng the young and old inA/ 40 /5L9 Engli sh Page I02 the Population than among the prime age popuracion, wbi.ch comprises tbe majority ofthe rabour force- This pattern of mortality declina has the expected effect on agest.ructure and relative 1abour supply: the proportion of the population at theyoung and old ages increases relative to those in the traditionar rabour forceages. To quantify this result, a simple comparison can be made of Cr{opopulations, Both experience the same level of fertility (a total fertility raCeof 5'0) but vary according to rheir rever. of mortality. The first popurationexhibits a life expectancy at birth of 40 years, typical of a country before theonset qf the norCality transition. The second population exhibits a lifeexpectancy of 65 years at birth, typicat of a country nearing the end of itsmortality transition. The described mortarity transition may be expected to takeplace over a quarcer-century or longer. Both populations are assumed to experrenceage-specific labour force participation rates typical of a country at a ,,middIe,, Level of modernization, !!/ and, for cbe sake of example, only the male popura tionhas been fipdeled. Results for females would differ only because of the .lifferentlevel of labour force participati.on exhibiteal.