Birth rates, or “total fertility rates” (TFR) are closely correlated with income levels.  The higher the income in an economic system and culture, the lower the birth rate.  In the Asian Tigers (Singapore, Taiwan, Hong Kong and South Korea), fertility plummeted with development, to levels insufficient to replace the population.  If these trends continue, the native populations of all the Tigers would effectively die out within about  a century, from The Economist

In the developing world as a whole, fertility rates fell by half, to three, in the 50 years to 2000. In South Korea the TFR fell by two-thirds in 20 years from the early 1960s. In Taiwan it dropped from 6.5 in 1956 to 2.2 in 1983 and 1.7 in 1986. So for three decades, fertility rates have mostly been below the “replacement” level—of just over 2.0 in rich countries. Last year the TFR was 1.22 in Singapore, 1.15 in South Korea and 1.04 in Hong Kong. In Taiwan it was 1.03, and the government’s planning agency forecast a further decline, to 0.94% in 2010, as women defer having babies during the Year of the Tiger (inauspicious, oddly). These are unprecedented levels for places unaffected by war or famine.

Given that declining fertility is tightly correlated with increasing income and development across all cultures and economic systems, what could possibly be its cause?

First, we must state the obvious premise underlying any analysis of cause and effect relationships:  Every effect has a cause.  (Unless you believe, like Stephen Hawking proposed in his new book, that the universe arose from nothing, in which case effects like the entire universe can magically arise, from nowhere, out of nothing).   In the animate world, every discernible effect must be presumed to be the product of a rational evaluation of the cost-benefit ratio of the course of action yielding it.   If flora and fauna were allowed to decide what to do with no consideration of the anticipated cost-benefit relationship of their action, the animate world would appear as nonsensical as a universe that could arise from nothing.  Action must be chosen that maximizes the welfare of the organism, or the organism would quickly die out, as other organisms making more efficient use of the available resources would crowd them out.  Cost-benefit analysis forms the foundation of evolution by natural selection.  ( That we need to reiterate the rationalist view that effects have causes is a reflection upon the near-mystical status of many of today’s “scientific” inquiries, especially those of theoretical physicists like Hawking.)

The cost-benefit inquiry for a course of action is conducted at the organism level, i.e., from the perspective of the individual actor.  In all of the cultures in which fertility is plummeting, women are free to decide how many children they wish to bear.  As economic development proceeds, the cost-benefit ratio of having children must  be changing from the perspective of the women making the decision of whether and how many children to have.  Females of child-bearing age must perceive that the costs of having children go up, or the benefits go down, or a combination of the two occurs, as economic development proceeds in order to yield the steep decline in birth rates. 

What might be some of the relevant costs?  There is the cost of finding an acceptable partner; the cost of physical discomfort and danger from bearing the child; the incremental cost of meeting the child’s essential needs;  the cost of education and training for the child, but most of all, the cost in time spent caring for the child.   In general, every moment spent caring for offspring is a moment that can’t be spent gainfully employed.  If the foregone wages are substantial, i.e., if the putative mother would otherwise enjoy a high hourly wage, the time anticipated to be spent caring for a child could prove very costly.

What of the benefits?  First, since only a very few folks in economically-developed societies live on farms, or even have their own proprietorships, the old idea that children are sources of cheap labor for the parents has to be abandoned for developed countries.  But, there is the benefit of companionship; the benefit of gaining a slice of immortality through the propagation of genes and memes in the child;  the joy of motherhood embodied in the nurturing care a child requires for the first years of its life, and the benefit of having someone to care for them when they grow old.    But in all societies that have grown rich and developed, the state provides help for the aged and infirm.  

What of other factors?  As economic development proceeds, information jobs increase and manual labor jobs decline.  Women have competitive equity, or even an advantage, relative to men in performing the tasks of information jobs–which they don’t have for jobs that require physical stamina and strength.   As information jobs gain in importance in an economy, women naturally stand to give up more and more by bearing children, even if the cultures of these advanced economies like to pretend that having babies doesn’t impair a woman’s ability to be competitively engaged in her occupation. 

Also, as women get ever more financially independent because of economic development, the old strategy of having babies to ensnare and obligate a man to provide support is abandoned.  A woman that has a better chance of employment than her male cohort is likely to do just the opposite–ensure she doesn’t have babies so she’s not saddled with having to support a man and his babies.

Thus, economic development carries with it the seeds of its destruction.   From the perspective of the females of child-bearing age, as economic development proceeds, children become more costly and less beneficial.   The resulting decline in birth rates ultimately causes population declines, which in turn  yields economic stagnation and contraction.  At which point, presumably somewhere along the continuum of population decline and economic contraction, the women decide to go back to having babies, else the society dies out.  No economic system has been rich long enough for plummeting birth rates to destroy it.  Yet.  We’re apt to find out in the next half-century, in the Asian Tigers and elsewhere, whether the unsustainably low birth rates reverse such that economic development doesn’t yield collective suicide.