In this connection, it should be borne in mind that while caring for the elderly can make demands on all family members, the brunt of the burden is undoubtedly borne by women (Allan, 1985), often by daughters-in-law in Japan. In conclusion, the Japanese model above-mentioned did perhaps nicely work out when mortality was high in the middle and old ages and there were few survivors of the elderly in the stem family households. In that situation, if they survived, they were hale and strong and particularly very useful with knowledge and skills they had accumulated. But when the life expectancy has increased dramatically and there are many survivors, some of whom are infirm and bedridden, it is not sure at all how long the three-generational family household as an optional mode of living arrangement for the elderly can last and can support such onus. But, on the other hand, it is also not sure whether the present model of the West letting the elderly make their own living in the spirit of independence and self-reliance to the latest possible limit can still work nicely in the prospect of further prolongation of life expectancy in the advanced ages and increases in the age segments that is what may be called "ageing within the aged".
Summary and Discussion
The imminent arrival of aged society is recognized as inevitable in Japan, inasmuch as it is an accumulated result of long past demographic trends. Even a drastic increase in fertility which may often be of involuntary nature cannot evade a collision course of population with a forthcoming ageing society, characterized by old-age dependency and the state in which there are more elderly people than children. Certainly, the term "population ageing" has become a household word to an average citizen in Japan. Population ageing has been considered one of the most crucial demographic and social issues facing contemporary Japan.
Contrary to the generally held notion that the prolongation of life expectancy brings about the process of population ageing, the established demographic theory teaches us that lowering fertility is the most important locomotive to reach population ageing. Usually, according to the experiences of recent demographic transition in both the developed and developing countries, increases in life expectancy have been brought up by sharp drops of mortality in infancy and childhood, rather than by mortality reductions in the middle and old-aged groups. Hence, assuming no fertility changes, an increase in life expectancy usually brings about population rejuvenation or population youthening. It is the fertility decline that changes the age profile of population. Fertility decline actually slices off the hefty population piece at the bottom of population pyramid, thus increasing proportion of the aged in the total population at the upper layers of the age profile. In recent years, however, the trend has changed slightly in such a way that mortality changes are more remarkable in the middle and aged groups of population than in the childhood, hence mortality decline in general means to work out more directly in increasing the sheer percentage of the middle and old level of populations.
