Low fertility rate reversal: a feature of interactions between Biological and Economic systems

An empirical relation indicates that an increase of living standard decreases the Total Fertility Rate (TFR), but this trend was broken in highly developed countries in 2005. The reversal of the TFR was associated with the continuous economic and social development expressed by the Human Development Index (HDI). We have investigated how universal and persistent the TFR reversal is. The results show that in highly developed countries, $ \mathrm{HDI}>0.85 $, the TFR and the HDI are not correlated in 2010-2014. Detailed analyses of correlations and differences of the TFR and the HDI indicate a decrease of the TFR if the HDI increases in this period. However, we found that a reversal of the TFR as a consequence of economic development started at medium levels of the HDI, i.e. $ 0.575<\mathrm{HDI}<0.85 $, in many countries. Our results show a transient nature of the TFR reversal in highly developed countries in 2010-2014 and a relative stable trend of the TFR increase in medium developed countries in longer time periods. We believe that knowledge of the fundamental nature of the TFR is very important for the survival of medium and highly developed societies.