According to the most recent UN estimates (United Nations 2017), almost one half of the world’s population lives in countries with below replacement fertility (BRF), i.e. with a total fertility rate (TFR) below 2.1 births per woman. Of these, one quarter have TFRs close to the replacement level, i.e. between 1.8 and 2.1; the other three-quarters have really low fertility, below 1.8 births per woman. Low-fertility countries are generally grouped into clusters. The main clusters are in East Asia, Southern Europe, the German-speaking countries of Western Europe, and all the former socialist countries of Central and Eastern Europe (Table 1).
In fact, contemporary fertility around the globe is lower than it has ever been. Since the middle of the 20th century, childbearing has declined by 50 percent: 50 to 60 years ago women in developed and developing countries combined had on average 5 children, but now the world average is about 2.5 children per woman.
Why do so many countries have below replacement fertility?
Early in the 20th century it became obvious that family size was declining in countries experiencing substantial industrial and urban growth. A number of French, British and American social scientists set out to map and explain this change. Perhaps the most comprehensive and profound explorations were conducted by a team of scholars at Princeton University’s Office of Population Research. Frank Notestein, its first director, outlined what had transpired by mid-20th century, including the main causes for the changing family size, in two papers dealing with what is now known as the “demographic transition” (Notestein 1945 and 1953). Much of the following summary applies even today:
The new ideal of the small family arose typically in the urban industrial society. It is impossible to be precise about the various causal factors, but apparently many were important. Urban life stripped the family of many functions in production, consumption, recreation, and education. In factory employment the individual stood on his own accomplishments. The new mobility of young people and the anonymity of city life reduced the pressures toward traditional behaviour exerted by the family and community. In a period of rapidly developing technology new skills were needed, and new opportunities for individual advancement arose. Education and a rational point of view became increasingly important. As a consequence the cost of child-rearing grew and the possibilities for economic contributions by children declined. Falling death rates at once increased the size of the family to be supported and lowered the inducements to have many births. Women, moreover, found new independence from household obligations and new economic roles less compatible with child-rearing (Notestein 1953:17).
Since then, fertility trends and levels, and their causes and consequences have been the most researched topics in population studies. However, despite the hundreds of published studies, it appears that Notestein’s observation continues to be valid: “it is impossible to be precise about the various causal factors, but apparently many were important”.