- National fertility and country-level general intelligence (G) negatively correlate.
- The frequencies of 8 SNPs that predict IQ also negatively correlate with fertility.
- Both findings are associated with Jensen effects.
- The SNP metagene negatively predicts fertility, when controlled for HDI.
- Global G should decline due to selection by − 0.253 points per decade.
Country-level total fertility rates (TFR) and cognitive ability are negatively correlated, suggesting the existence of a selection pressure that might be reducing global G. Also, the cross-population frequencies of several SNPs have been found to predict cognitive ability between countries. This study applies a cross-cultural sociogenetic approach to explore the role of latent factors among cognitive ability measures and these SNPs in moderating the associations among their indicators and TFR. Using a G factor constructed from five measures of cognitive ability, positive moderation is found on the TFR*ability relationship (ρ = 0.251 N = 60.6 countries). Using a metagene common factor among eight SNPs, positive moderation is also found on the TFR*SNP relationship (ρ = 0.816, N = 18 countries). An inference of polygenic selection for lower G is supported by the findings of two multivector co-moderation analyses. When controlled for one another, Human Development Index and metagene frequency both independently predicted TFR (β = − 0.339, and − 0.678 respectively, N = 18 countries). This indicates a joint impact of intelligent fertility control and life history slowing on the distribution of TFR values. Based on these results, polygenic selection might be reducing heritable G globally by − 0.253 points per decade, highlighting the importance of the Flynn effect as a contributor to global development.