Fertility and intelligence

The relationship between fertility and intelligence has been investigated in many demographic studies. 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. However, genetic studies have shown no evidence for dysgenic effects in human populations. Theories about dysgenic and eugenic effects in human populations have historically been associated with scientific racism. The negative correlation between fertility and intelligence (as measured by IQ) has been argued to have existed in many parts of the world. Early studies, however, were "superficial and illusory" and not clearly supported by the limited data they collected. Some of the first studies into the subject were carried out on individuals living before the advent of IQ testing, in the late 19th century, by looking at the fertility of men listed in Who's Who, these individuals being presumably of high intelligence. These men, taken as a whole, had few children, implying a correlation. 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, 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." 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. Other researchers began to report a negative correlation in the 1960s after two decades of neutral or positive fertility. In 1982, Daniel R. Vining, Jr.