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. 2014 Jan 29;281(1779):20132561.
doi: 10.1098/rspb.2013.2561. Print 2014 Mar 22.

Correlations in fertility across generations: can low fertility persist?

Martin Kolk  1 , Daniel Cownden, Magnus Enquist
Affiliations

Correlations in fertility across generations: can low fertility persist?

Martin Kolk et al. Proc Biol Sci. .

Abstract

Correlations in family size across generations could have a major influence on human population size in the future. Empirical studies have shown that the associations between the fertility of parents and the fertility of children are substantial and growing over time. Despite their potential long-term consequences, intergenerational fertility correlations have largely been ignored by researchers. We present a model of the fertility transition as a cultural process acting on new lifestyles associated with fertility. Differences in parental and social influences on the acquisition of these lifestyles result in intergenerational correlations in fertility. We show different scenarios for future population size based on models that disregard intergenerational correlations in fertility, models with fertility correlations and a single lifestyle, and models with fertility correlations and multiple lifestyles. We show that intergenerational fertility correlations will result in an increase in fertility over time. However, present low-fertility levels may persist if the rapid introduction of new cultural lifestyles continues into the future.

Keywords: cultural evolution; demographic transition; differential fertility; fertility; intergenerational transmission of fertility; socialization.

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Figures

Figure 1.
Figure 1.
Relative frequencies of PHH (blue, solid), PLH (green, dashed), PHL (purple, dotted) and PLL (red, dot-dashed) over time, after the manifestation of a new low-fertility lifestyle (model 1). We use the following initial values at t = 0: PHH(0) = 0.09, PLH(0) = 0.01, PHL(0) = 0.81 and PLL(0) = 0.09. The code to produce this figure can be found in electronic supplementary material, appendix B. (Online version in colour.)
Figure 2.
Figure 2.
Fertility and fertility correlations over time after the manifestation of a new low-fertility lifestyle (model 1). Dashed lines show fertility, solid lines show observed fertility correlations. The code to produce this figure can be found in electronic supplementary material, appendix B. (Online version in colour.)
Figure 3.
Figure 3.
Fertility and fertility correlations over time after the manifestation of a new low-fertility lifestyle, followed by the continuous introduction of new lifestyles (model 2). The dashed lines show mean fertility and the solid lines show observed fertility correlations. The parameter choices and code used to produce this figure can be found in electronic supplementary material, appendix C. (Online version in colour.)
Figure 4.
Figure 4.
Sketch of three different scenarios, each with different assumptions on fertility correlations across generations, showing implications for fertility (population size) and fertility correlations. (Online version in colour.)
See this image and copyright information in PMC

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