By Erich Striessnig, IIASA World Population Program

Credit: Héctor Gómez Herrero via Flickr (Creative Commons License)

Is replacement level fertility really the best for society? Maybe not, say IIASA researchers. Photo Credit: Héctor Gómez Herrero via Flickr (Creative Commons License)

When asked what a desirable fertility level for populations might be, most politicians, journalists, and even social scientists would say it is around two children per woman, as this would – on the long run – prevent a population from either exploding or dying out. Other reasons for championing replacement level fertility include maintaining the size of the labor force and stabilizing the dependency ratio. But what is the evidence for this rule of thumb?

My colleague Wolfgang Lutz and I aimed to answer this question in a new study published in the journal Demographic Research. We found, not surprisingly, that the optimal fertility level strongly depends on what you mean by optimal.

The criteria for optimal fertility have often been motivated by nationalistic desires for larger and thus more powerful nations. Today our concerns run more towards the dangers of overpopulation for the environment, the climate, and the limited resources on Earth, dampening the enthusiasm for high fertility rates. But as fertility rates fall in many countries around the world, there is a growing concern about aging populations and an increasing number of elderly depending on an ever smaller number of people actively participating in the labor force.

While all of these fears relate to the same problem – an unbalanced population age-structure – the resulting assessments of what level of fertility would be desirable completely ignore the heterogeneity of the population with regard to important demographic characteristics, especially the population’s education structure.

In our study, we wanted to account for the fact that more education not only has higher economic costs, including later entry to the labor market and higher life expectancy, which can hardly been seen as a negative effect. But education also leads to higher productivity, less unemployment, and a healthier workforce that would on average retire later. To include these factors in our assessment, we ran thousands of simulations using varying constant rates of fertility.

What we found is that when we factor in education, the level of fertility that on the long run would lead to the lowest level of dependency is well below the supposedly magical level of two children per woman.

We also tried to link the effects of different fertility rates to the resulting environmental burden by factoring in expected carbon emissions. Not surprisingly, higher rates of fertility lead to faster population growth and more emissions. That suggests that an environmentally aware society should aim for even lower fertility levels.

While our research is not intended to prescribe fertility levels for individuals and countries, the conclusions drawn from this thought experiment suggest that the widespread popular notions that current fertility levels–for example in France or the US are just right because they are around replacement level, whereas they are too low in countries like Germany or Austria–may be wrong. According to our new study, the opposite is true.

Striessnig, E, Lutz W. (2014) How does education change the relationship between fertility and age-dependency under environmental constraints? A long-term simulation exercise Demographic Research, 30(16):465-492


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