Watching Brigadoon the other day, and reflecting on age distribution in a society, got me to thinking. What are the influences of age-specific death rates on population age structure? More specifically, what would an “ideal” society look like if all of our dreams could come true?

Suppose every child was born healthy, lived for 80 years, and then died. Preferably peacefully, in her sleep. Suppose further that population is neither growing nor shrinking. What would the age distribution be, and what would be some of the consequences?

In this ideal world, each woman would have on average one daughter. (That would average out close to two children, if the ratio of boys to girls was even.) No doubt some would choose not to have children, and others would want more than two, but the average for a steady population with no premature death would be close to two children per woman.

Since there is no death before age 80, this would give an even age distribution—the number in any age category will be the same as in any other age category. The number under 5 would be exactly the same as the number 75 or over.

We do not expect children to support themselves. In our modern society we can hardly expect them to be truly self-supporting without a college degree—say 22 years of age, and for some careers even longer schooling is needed. And surely some respite from a lifetime of work is reasonable for those who have worked most of their lives. Let’s assume the average working life is 40 years. That would imply that half of the population was supporting the other half—whether through the relatives paying or through taxation and the government paying. It also implies a somewhat longer working life than is now considered ideal. (Note that support may well be work—such as raising and educating children—and not only money.)

In this country, most of the deviations from this picture are health-related. Our elders are often in need of care as well as support—especially for the last few years of their lives, and children are born with crippling health problems. People of all ages die, giving a pyramid-shaped age structure with more young people than old.  Wars can take out most of an age cohort. And we are certainly not keeping our numbers constant!

Let’s look at America in pre-revolutionary days. Assume that half of the children born do not live to have children of their own. Death at all ages is an accepted hazard—in particular, women often die in childbirth. Children are an economic asset—not only as farm labor, but as old-age insurance. The result will be a growing population if the average number of children per woman is more than 4. (From my own family history, it was often a lot more than 4.) It will also be a young population. There will be twice as many newborns as young people of an age to start families. There will be a further reduction through the child-bearing years, especially of women. While the maximum age may not change much, there will be far fewer older people.  Some variant of this as been the norm for most of our existence as a species. We almost expect slow growth in population, speeding up whenever new land is available.  This acceleration is often at the cost of populations formerly inhabiting that land.

What is happening now in third world countries follows neither of these models.

We try to avoid the deaths of children. Thanks to what we now know about epidemiology, immunization, such physical factors as mosquito netting, and the importance of clean drinking water we have cut down considerably on these deaths. Famine relief tends to be targeted at children.

But the inevitable result is the development of a population structure very heavily weighted toward the young. In particular there is a tremendous age bulge among adolescents and young adults, sometimes with little or no education, and sometimes with an education that leads them to despise the very culture that has kept them alive.

We have also exported our technology, which often means that jobs are available only to those with the education needed to operate the machines that do the labor.

I don’t know what the answer is, but in many ways we seem to have painted ourselves into a corner globally.  Is there an answer?