Factors Affecting the Number of Children in Five Developed Countries: A Statistical Analysis with an Evolutionary Perspective

  • Masahito Morita Department of Evolutionary Studies of Biosysteme, School of Advanced Sciences, The Graduate University for Advanced Studies (SOKENDAI)
  • Hisashi Ohtsuki
  • Akira Sasaki
  • Mariko Hiraiwa-Hasegawa
Keywords: developed country, fertility, fitness, number of children, statistical data


Evolutionary studies of reproductive fitness will lead to a deep understanding of the evolution of human behavior. However, empirical studies that include Japanese data are rare. We analyze statistical data that include subjects in five developed countries (Japan, South Korea, United States, France and Sweden). Distributions of the actual and desired numbers of children of people aged 45 or older peak at two in all countries. Our analysis shows that the unique factor that affects the actual number of children is the age of first marriage (in Japan and U.S.) or household income (in France). Other factors, such as education level, hardly affect the actual number or presence of children. We suggest directions of future studies from these results.

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