There is an inverse relation between cognitive ability and number of children; the effect is stronger among females than males; the effect appears to be increasing in strength over time. Notable limitations of the current literature are reviewed

A systematic review of the state of literature relating parental general cognitive ability and number of offspring. Charlie L. Reeve, Michael D. Heeney, Michael A. Woodley of Menie. Personality and Individual Differences, Volume 134, 1 November 2018, Pages 107–118. https://doi.org/10.1016/j.paid.2018.05.036

Highlights
•    The relationship between general cognitive ability and reproduction is reviewed.
•    There is an inverse relation between cognitive ability and number of children.
•    The effect is stronger among females than males.
•    The effect appears to be increasing in strength over time.
•    Notable limitations of the current literature are reviewed.

Abstract: The purpose of this study is to conduct a systematic review of the literature on the relationship between general cognitive ability and fertility among modern humans. Our goals were to (a) evaluate the state of the extant literature, and (b) provide a quantitative summary of effect sizes to the extent possible (given the limitations of the literature). A thorough search identified 17 unique datasets that passed the inclusion criteria. Using a Random Effects Model to evaluate the data, the overall weighted effect was r = −0.11, although the data also indicated a sex effect (stronger correlations among females than males), and a race effect (stronger correlations among Black and Hispanic populations compared to Whites). Importantly, the data suggest the correlation has been increasing in strength throughout the 20th century (and early 21st). Finally, we discovered several notable limitations of the extant literature; limitations that currently prohibit a psychometric meta-analysis. We discuss these issues with emphasis on improving future primary studies to allow for more effective meta-analytic investigations.

Keywords: Intelligence; Cognitive ability; ‘g’; Reproductive success; Meta-analysis; Dysgenic trend