There is evidence that, on a population level, measures of intelligence such as educational attainment and literacy are negatively correlated with fertility rate in some contexts.
[4] More rigorous studies carried out on Americans alive after the Second World War returned different results suggesting a slight positive correlation with respect to intelligence.
The findings from these investigations were consistent enough for Osborn and Bajema,[a] writing as late as 1972, to conclude that fertility patterns were eugenic, and that "the reproductive trend toward an increase in the frequency of genes associated with higher IQ [...] will probably continue in the foreseeable future in the United States and will be found also in other industrial welfare-state democracies.
"[6][b] Several reviewers considered the findings premature, arguing that the samples were nationally unrepresentative, generally being confined to white people born between 1910 and 1940 in the Great Lakes States.
[11] Critics note Vining's involvement with the white supremacist journal Mankind Quarterly and his acceptance of grants from the Pioneer Fund.
[21][c] Controversial psychologist Richard Lynn has been a well-known advocate for the validity of dysgenic hypotheses under modern conditions.
[31] Population economist Vegard Skirbekk on the other hand had already argued on the grounds of another large multi-national dataset that this characteristic "status-fertility relation" had long since stalled or even reversed for males just as well.
The higher the level of education and GDP per capita of a human population, sub-population or social stratum, the fewer children are born.
[46] In her review of reproductive trends in the United States, Van Court argues that "each factor – from initially employing some form of contraception, to successful implementation of the method, to termination of an accidental pregnancy when it occurs – involves selection against intelligence.
[52][53][54][55] Preston and Campbell (1993) argued that it is a mathematical fallacy that such differences in fertility would result in a progressive change of IQ, and applies only when looking at closed subpopulations.
[56] However, James Samuel Coleman, formerly president of the ASA such as economist David Lam both independently argued that this model depends on various assumptions which are unlikely to be true.
[57][58] Recent research has shown that education and socioeconomic status are better indicators of fertility and suggests that the relationship between intelligence and number of children may be spurious.
Among women, a post-hoc analysis revealed that the lowest and highest intelligence scores did not differ significantly by number of children.