Intelligence and family size: A paradox resolved

The reproduction of intelligence

“…During the first half of the century, studies in Britain and the United States usually found a negative relationship between IQ and completed family size (Anastasi, 1956;Cattell, 1936Cattell, , 1937Dawson, 1932/33), although atypical results were obtained occasionally (Willoughby & Coogan, 1940). These early results were challenged by a series of studies with mainly White middle-class groups in the United States at the time of the baby boom, which reported a negligible or slightly positive relationship between IQ and number of children (Bajema, 1963(Bajema, , 1968Falek, 1971;Higgins et al, 1962;Waller, 1971). These results were complemented by the observation that subfertility of men in Who's Who in America disappeared for cohorts born after 1910 (Kirk, 1957).…”

“…2% in 1960to 48.9% in 1980(US Census Bureau, 2008. Observations on differential reproduction during the 1960s (Bajema, 1963(Bajema, , 1968Falek, 1971;Higgins et al, 1962;Waller, 1971) show that the earlier expansion of secondary education in the United States (Goldin & Katz, 1999) did not seem to impair the reproduction of educated women to any great extent, but the later expansion of tertiary education did.…”

New evidence of dysgenic fertility for intelligence in the United States

“…If these had low IQs, their lack of children would counterbalance the dysgenic fertility inferred from the negative association between intelligence and numbers of siblings. Studies by Bajema (1993) and Higgins et al (1992) reported that childlessness was most prevalent among those with very low IQs. These results have been widely considered to invalidate the methodology of inferring that fertility was dysgenic from the negative associations between intelligence and numbers of siblings (e.g., Ehrlman & Parsons, 1976).…”

“…First, it goes some way towards resolving the problem of the differences between the Higgins et al (1992) and the Bajema (1993) studies, showing a positive relationship between intelligence and fertility, and the Van Court and Bean (1985), Vining (1982Vining ( , 1995, and the Retherford and Sewell (1988) studies, showing a negative relationship. The results of the present study confirm and extend the second set of studies in that they show that the association between intelligence and fertility has been consistently negative for all birth cohorts from 1900-1919 up to 1970-1979.…”

“…Osborn called this the ''eugenic hypothesis.'' Some studies carried out in the United States in the 1960s suggested that dysgenic fertility had already disappeared and therefore that the eugenic hypothesis was right (Bajema, 1993;Higgins, Reed, & Reed, 1992). However, several studies in the 1980s found that dysgenic fertility was still present (Retherford & Sewell, 1988;Van Court & Bean, 1985;Vining, 1982).…”