ONE of the paradoxes of human biology is that the rich world has fewer children than the poor world. In most species, improved conditions are expected to increase reproductive efforts, not reduce them, but along with economic development, country after country has experienced what is known as a demographic transition: fertility (defined as the number of children borne by a woman over her lifetime) down from about eight to near one and a half. That number is so small that even with the decline in child mortality that usually accompanies development, it is not possible to sustain the population.
The collapse of this reproduction is very worrying because it comes along with an increase in life expectancy which shows that, by the middle of this century, populations in the most developed countries will not only shrink (unless they are supported by enormous historical levels). immigration) but also that the number of retirees supported by every working age person will increase significantly. However, if Mikko Myrskyla from the University of Pennsylvania and his colleagues was right, things might not be that bad. A study they just published in Nature shows that along with development, the demographic transition is reversed.
Dr. Myrskyla sees the world as it was in 1975 and as it is now (or, at least, as in 2005). He compared two things. One is the total fertility rate (the number of children to be born by a woman in a particular country during her lifetime if she experiences an age-specific fertility rate observed in that country during the calendar year concerned). The other is the human development index for the country. HDI, a measure used by the United Nations, has three components: life expectancy; average income per person; and education level. The maximum possible value is one.
Back in the 1970s, no country approached any. Of the 107 places the researchers saw, the best was Canada, with a HDI of 0.89. However, in 2005, things improved. Two dozen of what is now 240 countries have HDI above nine – and something extraordinary has happened. Back in 1975, a graph depicting fertility rates for HDI fell when HDI rose. But in 2005, the line had a kink in it. Above HDI 0.9 or higher, appears, producing what is known in jargon as a “J-shaped” curve (even though it is a mirror image of the letter J). As the graph shows, in many countries with very high development rates (around 0.95) fertility rates are now approaching two children per woman. There are exceptions, especially Canada and Japan, but the trend is clear.
MB: Shocking! The trend is clear, when countries or even households become more advanced and financially stable they have lower fertility rates. Why is more than that our human psychology works in an irregular way; households must want more children because they can afford it no less. I am sure there are a number of explanations for why this phenomenon occurs; but I feel there is a big factor related to rich people who are spent with work, which results in less time for family or more children. Can anyone think of other possible social factors (such as the role of women in households in developed countries) that can contribute to logical behavior?