The Economist reported this week that falling fertility rates around the world spell doom for many countries as the single life appeals to more women than replacing themselves through children.
For hundreds of years, the world's population has grown steadily. But demographers now believe that within several decades, the number of people on earth will actually begin to decline.
Women in the wealthier parts of Asia, for example, are literally on a "marriage strike" leading to a drop in birth rates.
The United Nations reports women in 83 countries and territories around the globe won't have enough daughters to replace themselves unless fertility rates suddenly rise.
"What we're seeing now in many countries is the drop in fertility is so fast, it's literally without precedent in human history,” said Phil Longman, a demographer at the New America Foundation research group in Washington D.C.
"What it's going to mean is that countries like China for example, are going to age in a single generation as much as countries like France aged in 150 years," said Mr. Longman.
Fertility specialist Rima Abdul said there are several reasons for the decline. "We have increased pollution, increased toxins in the food supply and its packaging, increased toxins in our water supply, and increased toxins in pharmaceutical drugs and vaccinations which all inevitably leads to a decrease in fertility rates in developed nations," she said.
Sub-replacement fertility is a total fertility rate (TFR) that (if sustained) leads to each new generation being less populous than the previous one in a given area. In developed countries sub-replacement fertility is any rate below approximately 2.1 children born per woman, but the threshold can be as high as 3.4 in some developing countries because of higher mortality rates.
The total fertility rate (TFR, sometimes also called the fertility rate, period total fertility rate (PTFR) or total period fertility rate (TPFR)) of a population is the average number of children that would be born to a woman over her lifetime if (1) she were to experience the exact current age-specific fertility rates (ASFRs) through her lifetime, and (2) she were to survive from birth through the end of her reproductive life.
A population that maintained a TFR of 2.0 over a long time would decline (unless it had a large enough immigration). However, it may take several generations for a change in the total fertility rate to be reflected in birth rate, because the age distribution must reach equilibrium.
a list of dependent territories by their TFR.
Using Hong Kong as an example, 1,000 women there are expected to give birth to 547 daughters. Those daughters would in turn be succeeded by only 299 daughters and so on.
At that rate, Hong Kong's female population would shrink from 3.75 million to just one in 25 generations. The last female would be born in 2798.
If you apply that theory to Japan, Germany, Russia, Italy and Spain, their populations won't last out the millennium.
Canada's last woman, using current statistics, would be born sometime around 4400.
And, China isn't about to save the world from eventual declining fertility rates either. Using the same UN population figures, it has a mere 1,500 years left before it too can't replace its women.
Richard Jackson, head of the global aging initiative at the Center for Strategic and International Studies in Washington D.C., says that falling fertility and longer life spans have created a new demographic time bomb.
How countries meet those challenges could prove pivotal to the stability of these countries in the 21st century.
"We have so many scientists speaking about forcibly depopulating the earth when it's depopulating itself, but this must be reversed if the human species is to ever endure the test of time," said Abdul.