Populations are meant to increase. Or put another way, children keep being born. For a very long time, human beings have believed that this is the way society operates. Since our distant ancestors appeared in central Africa over the several million years ago, human beings have been bearing children and with each generation, the population has been increasing. Then as they migrated east and north, they began to settle around the world, eventually covering the entire earth.

However, at the end of the twentieth century, the advanced industrialized countries began to experience a decline in the rate of population growth, in particular, some countries in Scandinavia and Asia. This meant that population growth had slowed down.

In affluent countries, a decline in the birth rate seems to occur in parallel with demographic aging. A decline in the birth rate means both a drop in the percentage of children born and also in the number of births. Demographic aging refers to a marked increase in the ratio of people aged 65 or over to the rest of the population.

The United Nations has established numerical criteria for demographic aging, but not for the declining birth rate. In other words, an aging society is defined as one in which those 65 years of age or older make up 7% or more of the total population, and when this percentage reaches and continues to remain at 14% or more, it is considered to be an aged society.

The advance of demographic aging and an increase in the elderly population are relatively easy to explain. It is related to the fact that the quality of daily necessities, that is, food, shelter and clothing, has improved for the elderly. This can also be attributed to the medical system, one of the social systems that is particularly good in Japan and in Scandinavia.

Although the rate of population increase is said to have begun declining at the end of twentieth century, why did it accelerate population growth to such an extent? As in the case of demographic aging, this can also be explained by the quality and quantity of food, clothing and shelter. We know that the current affluence is the result of scientific and technological progress since the start of the twentieth century. Food, shelter, and clothing are, of course, supported by science and technology. In particular, not only do we rely on technology in agriculture, animal husbandry and the fishery industry to increase the plants and animals that become food, but also on biotechnology which plays a large role in food production. With the advance of technologies, they are contributing to the supply of high-quality food and food products in adequate quantity.

So, why did rate of population increase begin to slow down in the latter half of the twentieth century, particularly, at the turn of the century? As a physician, the first image that comes to mind is the phenomenon of bacterial growth. Fill a flask with culture solution, drop a tiny spoonful of bacteria into it, heat it to the appropriate temperature and the bacteria will multiply rapidly. After some time, however, bacterial growth begins to slow down and the bacterial count stabilizes at a fixed level, which is then maintained for a period of time until it begins to decline. This decline occurs despite the fact that an adequate nutrient level remains in the culture solution. This has been attributed to the increased metabolite concentration that bacteria have used as nutrition or a change in the pH level or other survival conditions.

Since humans and bacteria are too distantly related, let me introduce an experiment with a smaller animal such as the mouse. It is said that when a considerable number of male and female mice are raised in a cage of certain dimensions, their numbers increase with the birth of offspring, but when conditions become crowded, conflict occurs even when there is sufficient food, and females stop paying adequate attention to child-raising, and the number of offspring then declines.

The results of this experiment bring a biological perspective to the issue of population growth. In the case of microorganisms, chemical factors such as the nutrient and pH level appear to play a large role, but in the case of small animals, in addition to chemical and physical factors, behavior and information are also at work. In the case of humans, the factors are more complex and the role of information is much greater.

Consequently, the destruction of the population myth began when human beings began to sense in various ways that populations had increased all over the world and began to take action to halt this increase. Women, being more sensitive than men to this, seem to have taken a stand to decide themselves whether to give birth or not.

Of course, there are many ways of looking at the declining birth rate and demographic aging, which are complicated social issues that cannot be easily explained. According to demographers, the main reason is that couples, even after marrying, no longer bear children. For a pediatrician, this is a sad situation. Another major reason is that men and women of marriageable age do not focus on getting married.

Although I am not sure how economists give a value to children, but it is said the economic value of children has decreased. Furthermore, with increased participation of women in the workforce, society has become affluent, the cost of childbirth and raising children has sharply increased as well, and women do not want to forsake the employment opportunities that they have finally obtained. In addition, the economic recession has put pressure on household finances so that the cost of child-raising and education now feels relatively more burdensome.

Sociologists argue that the declining birth rate is due to disillusionment with gender discrimination in Japanese society by women, which has engendered a quiet resistance on their part. On the other hand, social psychologists identify a tendency toward upward mobility and claim that women seek to marry men with better future prospects than their own father, but no longer see this as a possibility amid the current economic downturn.

Developmental psychologists see the loss of the father in the postwar period and his absence from the house due to the employment system as one cause of the "parasite single" phenomenon, which refers to children who are spoiled, unable to leave home, or even get married.

Each field gives a different explanation from its respective standpoint, but mainly, they all consider the declining birthrate and demographic aging to result from a situation in which the current affluence must be maintained by the increased participation of women in the workforce although the current system does not allow women to both work and raise children. Moreover, the current social system makes it difficult for young people, women, in particular, to look forward to marriage and having children in the future. What we need now is a change in our thinking and to establish child caring design in society so that women can both raise children and work. And so that children can live life full of joy.