<p>Over the past decades, unexpected reductions in fertility have resulted in a growing number of nations facing serious population declines. Experts remain uncertain about which psychological mechanisms contribute to declining reproduction and have not yet identified effective countermeasures. Evolutionary psychology is well-positioned to investigate this problem, yet as a field it has primarily examined sexual psychology in largely non-reproductive populations, leaving an important explanatory gap concerning reproductive psychology, especially among women. This theoretical and synthetic interdisciplinary article addresses that gap in three ways: it identifies a mismatch between contemporary evolutionary research on mating and actual reproductive decision-making; it proposes Young Female Syndrome as a conceptual target for understanding how contemporary environments may impact female reproductive strategies; and it outlines a research program linking macro-level fertility correlates to evolved reproductive psychology. It also argues that broader historical context is important for understanding current fertility decline. Across the past eight centuries, the West’s three sexual revolutions have produced a novel mating environment that may be affecting female sexual strategies, pair-bonding, and reproduction in ways that remain poorly understood. Addressing this challenge requires integrating evolutionary, economic, cultural, and psychological perspectives in order to clarify how major social changes influence human reproductive decision-making.</p>