Population Where We Stand Now

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The size of the human population will depend upon, among other things, both the average level of affluence and the technology (and resources) used to support that affluence. However, it seems certain that, with foreseeable technologies and with a standard of living near that now enjoyed by the rich nations (and aspired to by the poor), our "optimum" population would be substantially smaller than today's ... perhaps one billion or less.

UNDERSTANDING GROWTH RATES

Of course, the human population is now moving away from an optimum level, and is actually increasing by some 75 million people annually. But there has been a cheering decline in birth rates in rich countries and, more important, in quite a few poor ones.

In the wealthy nations, growth rates have declined considerably. Some of these lands (such as Austria, East Germany, Sweden, and the United Kingdom) have in essence reached zero population growth (ZPG) ... and West Germany's population is gradually shrinking. Unfortunately, however, the rich nations with slow growth represent only about a quarter of humanity. And in the poor three-quarters, the numbers are still skyrocketing.

There are two reasons for these increases. First, birth rate decline, where significant, is still small in proportion to what is needed. For example, although India's birth rate has gone down from about 42 per thousand to 36 per thousand in the last decade or so, its target rate should be below 18. And in some areas, such as much of Africa, there hasn't been any significant decline in birth rates.

The second reason for our continuing population problems is the momentum built into expansion by virtue of the age composition of rapidly growing societies. These typically have a high proportion of young people—often 45% or more—under the age of 15. This means that, even after family sizes become small, the population will continue to increase for a long time.

How can this be? After all, once each couple has an average of just over two children, in effect (or so it would seem) simply replacing itself, shouldn't population growth stop? (The "just over" two children figure allows for those infants who die before reaching reproductive age.)

Sadly, the answer is no. ZPG occurs when birth rates and death rates are equal... reducing a nation's reproduction rate to replacement level does not bring about ZPG immediately because of the inherent youth-heavy age composition of growing populations. There are, of course, many more young people to marry and have babies in such a population than there are elderly.

Thus, parents aged 20 to 30 may have only two children, but chances are they will still be alive, aged 40 to 50, when their children reach reproductive age. In this case the generations would be just replacing themselves, but they would go on living after they reproduced, while the next generation would add more babies to the population. The death rate would not begin to rise Significantly until one or two decades later, when people of that first replacement reproducer generation reached their 60's and 70's. And at that time, their grandchildren, the third generation, would be having their children.

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