But we must carefully examine the assumptions behind such projections.
And forecasts that population is going to level off or decline this century have been based on the assumption that the developing world will necessarily follow thepath of the industrialized world. Eyeing the future, conservationists have clung to the notion that population will peak and then start to decline later this century. Wilson has propounded what he terms the bottleneck theory: that maximum pressure on the natural world will occur this century as human population peaks, after which a declining human population will supposedly ease that pressure.
But will such low levels find favor in the Nigerias, Pakistans, and Zambias of this world?
The desire for more than two children — often many more than two — will remain an obstacle and will challenge assumptions that world population will level off or decline.
Clearly, not all countries will see a continuous decline in fertility rates, and some have barely begun to drop, meaning that projected population sizes will turn out to be too low.
Fertility rates are lowest among educated, urban women who account for much of the initial decrease.
A central tenet of demography is that global population will peak at 9 to 10 billion this century and then gradually decline as poorer countries develop.
But that assumption may be overly optimistic — and if it is, population will continue to rise, placing enormous strains on the environment. Leading demographers, including those at the United Nations and the U. Census Bureau, are projecting that world population will peak at 9.5 billion to 10 billion later this century and then gradually decline as poorer countries develop. What if population continues to soar, as it has in recent decades, and the world becomes home to 12 billion or even 16 billion people by 2100, as a high-end UN estimate has projected?
First, that it will continue to decline where it has begun to decline, and will begin to decline where it has not.
Second, that the decline will be smooth and uninterrupted.