Human genealogy reveals a selective advantage to moderate fecundity

Abstract

Life-history theory suggests that the level of fecundity of each organism reflects the effect of the trade-off between the quantity and quality of offspring on its long-run reproductive success. The present research provides evidence that moderate fecundity was conducive to long-run reproductive success in humans. Using a reconstructed genealogy for nearly half a million individuals in Quebec during the 1608–1800 period, the study establishes that, while high fecundity was associated with a larger number of children, perhaps paradoxically, moderate fecundity maximized the number of descendants after several generations. Moreover, the analysis further suggests that evolutionary forces decreased the level of fecundity in the population over this period, consistent with an additional finding that the level of fecundity that maximized long-run reproductive success was below the population mean. The research identifies several mechanisms that contributed to the importance of moderate fecundity for long-run reproductive success. It suggests that, while individuals with lower fecundity had fewer children, the observed hump-shaped effect of fecundity on long-run reproductive success reflects the beneficial effects of lower fecundity on various measures of child quality, such as marriageability and literacy, and thus on the reproductive success of each child.

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Fig. 1: Time between marriage and first birth.
Fig. 2: Overview of the proposed hypothesis.
Fig. 3: Predicted numbers of children and great-great-grandchildren.

Data availability

The data that support the findings of this study are available from PRDH at the University of Montreal. Restrictions apply to the availability of these data, which were used under license. They are available from the authors upon reasonable request and with permission of PRDH.

Code availability

The statistical code is available from the authors upon request.

Change history

  • 10 April 2019

    The original Nature Research Reporting Summary provided with this manuscript was incorrect. The correct version is now available online.

  • 08 May 2019

    In the version of this article initially published, several sentences contained errors. The sentence “Moreover, the analysis further suggests that evolutionary forces decreased the level of fecundity in the population over this period, consistent with an additional finding that the level of fecundity that maximized long-run reproductive success was above the population mean” contained an error. The word “above” should have been “below”. Also, the sentence “Interestingly, the PI associated with the peak of the hump is above the mean and median PI in the population (Supplementary Table 3), in accordance with the finding that evolutionary forces decreased the mean PI in the population over the time period” contained an error. The word “decreased” should have been “increased”. Finally, the sentence “Hence, consistent with the finding that the level of fecundity that maximized long-run reproductive success was above the population mean (that is, 62 weeks), as well as the population median (that is, 53 weeks), evolutionary forces operated towards an increase in the mean PI over these 4 generations from 62.4 to 66.2 weeks” contained an error. The word “fecundity” should have instead been “PI”. The errors have been corrected in the HTML and PDF versions of the article.

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Acknowledgements

The data were collected and kindly provided by ‘Le Programme de Recherche en Démographie Historique’ (PRDH) at the University of Montreal. The authors are grateful to B. Desjardins for sharing the data and providing helpful information. Part of this research was conducted while M.K. was a visiting assistant professor at Brown University and a visiting scholar at Harvard University, and funded by the Carlsberg Foundation, the Danish Research Council (reference numbers 1329–00093 and 1327–00245) and the European Union’s Horizon 2020 research and innovation programme (Marie Skłodowska-Curie grant agreement number 753615).

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O.G. and M.K. conceived the research idea, formulated the theory, analysed the data and wrote the manuscript.

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Correspondence to Oded Galor or Marc Klemp.

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These authors contributed equally: Oded Galor, Marc Klemp.

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Supplementary Information

Supplementary Sections 1–13 and Supplementary Bibliography

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Galor, O., Klemp, M. Human genealogy reveals a selective advantage to moderate fecundity. Nat Ecol Evol 3, 853–857 (2019). https://doi.org/10.1038/s41559-019-0846-x

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