The Cool Water condition is a climatic configuration that combines periodically frosty winters with mildly warm summers under the ubiquitous accessibility of fresh water. Historically, it embodied opportunity endowments that weakened fertility pressures, resulting in household formation patterns that empowered women and reduced gender inequality. Reviewing the literature on the deep historic roots of gender inequality, this paper theorizes and provides evidence for a trajectory that (1) originates in the Cool Water climatic configuration, (2) leads to late female marriages in preindustrial times, and (3) eventually paves the way for various gender-egalitarian patterns of the present.