Alloparenting by and with genetically unrelated individuals is evolutionarily novel; thus, the Savanna–IQ Interaction Hypothesis predicts that more intelligent parents are more likely to resort to paid childcare by strangers. Analyses of individual data (National Child Development Study) in the United Kingdom (Study 1) and macrolevel data from the United States (Study 2) and economically developed Organization for Economic Cooperation and Development (OECD) nations (Study 3) confirmed the hypothesis. Net of education, earnings, sex, current marital status, and number of children, more intelligent British parents were more likely to resort to paid childcare at ages 33 and 42; net of female labor force participation rate, median household income, median cost of childcare, and mean education, U.S. states with higher average intelligence had higher proportions of children (ages 0–4) in paid childcare; and net of maternal employment, gross domestic product (GDP) per capita, cost of childcare, and female educational attainment, OECD nations with higher average intelligence had higher proportions of infants (ages 0–2) in paid childcare. The results were remarkably consistent; both across the 50 U.S. states and 45 economically developed OECD nations, a one IQ point increase in the average intelligence of the population was associated with a 1.8% increase in the proportion of children in paid childcare. Contrary to earlier findings, there was some suggestive evidence that the experience of paid daycare might harm the cognitive development of children. The studies point to the importance of evolutionary perspective in developmental psychology and child development. (author abstract)