To further elucidate the relative weight of various factors in shaping women’s fertility in low birth-rate societies like China, the author proposes an evolutionary framework of planned reproductive behavior and a series of its propositions about the second-child intentions and behavior, the key to understanding low-fertility behavior. Such propositions receive substantial support from the dominance analysis of the longitudinal data from a sample of one-child mothers in China. All nuclear-family members were complete stakeholders of reproduction: The fertility attitude of the mother’s husband, i.e. husband-specific injunctive norms, made the largest contribution to fertility intention, followed by her own and firstborn’s attitudes. Among incomplete stakeholders, the injunctive norms from parents were more important than those from peer relatives and friends in predicting fertility intention, but the opposite held for descriptive norms, i.e. actual number of children. Regarding the actual fertility behavior followed over 2.5 years, fertility intention was the dominating predictor of it; fertility attitudes of all three nuclear-family members were equally important predictors; by contrast, the injunctive norms from all incomplete stakeholders were of no importance. Perceived challenge in investing in children was an important predictor of both fertility intentions and behavior, but other constraints only became important at the latter stage. The study articulates the theoretical underpinnings of the collective decision-making in family reproduction through a behavioral ecology lens, suggests cultural evolution of fertility by horizontal transmission of new pronatalist norms in current China, and has potential implications for population policies in low-fertility societies.