Social determinants of low fertility in Asia: a comparative review of trends in East, Southeast and South Asia.

Asia, home to nearly 60% of the world's population, is central to global demographic change. Fertility trajectories shape population growth, aging, and decline, with implications for labor supply, economic development, family structures, and caregiving. Studying these patterns offers critical insights into the future of population size, structure, and human potential both regionally and globally. This paper addresses gaps in the largely snapshot, country-specific literature by providing a six-decade comparative overview of fertility trends in East, Southeast, and South Asia, with emphasis on their social determinants. Fertility is shaped not only by individual choice or biology but also by broader socioeconomic, cultural, and policy contexts that influence proximate factors of fertility such as union patterns, contraception, postpartum infecundability, and abortion. We identify distinct regional trajectories of fertility decline, examine their underlying drivers, assess the applicability of prevailing theories, and propose an Asymmetric Adaptation Framework to explain Asia's fertility transitions. While socioeconomic development and ideational change have shaped fertility behavior, cultural factors-such as religion, colonial legacies, kinship systems, and family policy-are pivotal in Asia. Certain trends cannot be explained by socioeconomic development alone, reflecting deeper historical and cultural roots. The Asian experience highlights the limits of prevailing Eurocentric, unidirectional theories and underscores the need for regionally grounded explanations that account for the interplay of structural forces, cultural norms, historical contexts, and policy in shaping fertility decline.