In the early 1970s, demographers began to spot a new pattern of human behavior that they had never seen before. In 1970, when Sweden, Finland and Denmark conducted their annual tallies of births and deaths for the previous year, the numbers suggested that young adults were having so few children that they would not succeed in replacing their generation.
This finding contradicted all reigning theories of human population. Until then, demographers, as well as thinking people in general, had always believed that human beings would inevitably produce more than enough children to sustain the population -- at least until plague, famine or nuclear winter set in. It is an assumption that not only conformed to our long experience of a world growing evermore crowded, but that also enjoyed the endorsement of such influential thinkers as Thomas Malthus and Charles Darwin.
At first, the exceptionally low birthrates that first appeared in Scandinavia were dismissed as an anomaly or measurement error, yet by now the phenomenon has spread around the world. For more than a generation now, people living in well-fed, healthy, peaceful nations have been producing too few children to replace themselves. This is true even though dramatic improvements in infant and child mortality mean that far fewer children are needed today -- only about 2.1 per woman in modern societies -- to avoid long-term population loss. Today, birthrates have fallen below replacement levels not only in every European country, but in nations rich and poor around the globe -- from China, South Korea, Japan, Australia and Singapore, to Canada, Brazil, Chile, the Caribbean and Russia, and even in parts of the Middle East, including Lebanon, Tunisia and Iran.