while mortality decline generally has little effect or, at best, promotes population rejuvenation.
If a longer period is used to decompose the change in the percentage of the population aged 65 and over, the effect of fertility is always larger than that of mortality: see, for example, the 35-year time period between 1950 and 1985 in Table 5, where the effect of fertility was even larger than the effect of the initial age distribution.
Perhaps, in this moment, it is useful to refer to a chart showing changes in age-specific mortality for males and females separately. Figure 8 indicates age-specific patterns of mortality for 1921-1925, 1960 and 1990,separately, over several decades. Notice that this chart is based on the semilogarithmic graph. From this chart, some salient features may be pointed out.
(1) The decline in infant and child mortality from 1921-25 to 1990 is very significant.
(2) What may be called "tuberculosis lump" appeared in 1921-25 at ages between 15 and 25 have virtually disappeared among females in 1990.The recurrence of a lump or bump around age 20 among males in 1990 should be considered to be caused by external cause of death, notably attributable to motor-bike accidents.
(3) On the other hand, however, the mortality improvements are not particularly phenomenal at advanced ages, though the nature of semilogarithmic graph might disguise some appreciable changes.These charts may suggest that increases in life expectancy occurred in the postwar years were largely attributable to the rapid declines in infant and child mortality. This pattern of trends is also observed widely inpresentday developing countries since the mortality can be more easily reduced in the young age groups rather than in the elderly. Mortality in childhood is caused mainly by infectious and parasitic diseases which can be more easily controlled by the anti-biotics and modern medical technology. On the other hand, however, mortality in the old ages is not easily controlled even by modern medical technology since diseases characteristic of old-ages are of attritional and degenerative nature of human organs.Hence, if other things being equal, the remarkable reductions in mortality in the infancy and childhood have an immediate effect of expanding the bottom part of the population pyramid, thus youthening or rejuvenating population, rather than ageing population.
Table 6 indicates the rate of contribution of improvement in mortality in each age group to the lengthening life expectancy in Japan. Accord
