<p>Social attitudes are heritable behavioral dispositions and therefore, evolvable human traits; despite this, their associations with fertility as a crucial marker of evolutionary fitness are rarely examined. We used a publicly available, large intercultural dataset (<i>N</i> = 78754; 72 countries) to empirically explore the associations between conservative social attitudes (i.e., right-wing ideology, a lack of support for gender equality, self-reported religiousness, and preference for religiousness in romantic partners) and fertility, measured as the number of children. The results showed that all examined attitudes positively predicted fertility across countries; nevertheless, considerable variation in regression slopes between the countries was also detected. Small quadratic effects were found, suggesting that individuals with the strongest expression of these attitudes had an additional non-linear increment in fertility. Right-wing ideology and low preference for gender equality were more strongly associated with fertility in women than in men. Self-reported religiousness was strongly associated with a preference for the same trait in romantic partners; furthermore, an interaction between these two traits in fertility prediction was also found, showing that low self-reported religiousness combined with low preference for religious partners predicts additional decrease in fertility. Present findings suggest that conservative social attitudes may be under positive directional selection and could be evolving in contemporary humans, contributing to both human evolutionary ecology and behavioral demography.</p>