The demographic transition

All of this neatly fits the concept of the "demographic transition," first observed in the two centuries preceding 1950 in what are today's developed countries.⁴ Prior to the transition, these northern countries experienced high death rates matched by high birth rates, resulting in a relatively stable population size over time. But then improving living standards and public health measures caused death rates to drop, followed by a gradual drop in birth rates, which by the 1970s once again matched death rates. Between the onset-of-mortality decline and the drop in birth rates, population surged in northern countries, actually quadrupling. But that is long over, and most developed countries are now projected to experience population shrinkage in the future.⁵

Demographers long posited that today's third world countries would undergo a similar transition. Indeed, in the period following World War II, mortality decline accelerated in developing countries.⁶ As the demographic transition model would predict, that led to a surge in population growth. And as expected, the death rate decline was later followed by a compensatory drop in birth rates. Instead of taking two centuries for the process to complete itself, this time it appears it will happen in less than one century.

Based on new data on fertility decline, the United Nations projection of the size the human population will reach in the year 2050 is now 9.37 billion, about 50 percent larger than today's population.⁷ While that may still seem large, the new estimate is down from the 11.16 billion that was projected just twenty years ago.⁸ The population is projected to stabilize shortly thereafter, most likely below 11.5 billion.⁹ As noted in chapter 1, that is within the levels that most experts estimate the earth could support.

If that is so, then why all the fuss? It seems that many nondemographers either lost sight of, or never really understood, the nature of the demographic transition. Terrified by the apparently exponential growth of third world populations, which they assumed would continue to grow explosively until checked by massive famine and epidemics, these analysts generated alarmist predictions. In his 1968 best-seller The Population Bomb Paul Ehrlich wrote: "The battle to feed all of humanity is over. In the 1970s the world will undergo famines-hundreds of millions of people are going to starve to death. . . ."¹⁰ Similar treatises have been written over the years by others, such as Lester Brown of the WorldWatch Institute.¹¹ Though starvation on the scale predicted by Ehrlich has not occurred, he repeated the warning in 1990 in The Population Explosion.¹²

Ironically, these warnings came just as demographers were announcing that fertility was starting its decline in the last regions of the world, beginning the final phase of the demographic transition.¹³ Of course, once fertility rates drop, there is a time lag before population-growth rates fall, as people who are now children come into their child-bearing years.

While the final phase of the transition seems to have begun everywhere, concern remains as to its pace and irreversibility. Organizations that earlier advocated population control programs to avert famine and environmental catastrophe, now say that precisely these programs have brought fertility down. They argue that population control efforts must be redoubled to assure that the gains are not reversed and that the subsequent declines in population-growth rates come quickly enough to avoid too many more people being born in the interim.¹⁴ In order to address these concerns we must examine the specific mechanisms that make some countries move more quickly through the phases of transition than others. We will do that in a later section of this chapter on the causes of fertility decline.

As a conclusion to this section, however, we can say with confidence that there is abundant evidence that the human population-growth rate is slowing and will eventually stop. It is hardly out of control. Populations will continue to grow rapidly for several decades before leveling off in many third world countries, but that does not, in and of itself, mean that population density or growth causes hunger in our world, an issue we address in the following section.