Between Brothers and Beyond: The Cultural Evolution of the Naxi in the Wake of Polyandry’s Decline

Abstract

Why has polyandry, where multiple men, typically brothers, share a single wife, persisted for centuries among the Naxi of Eya, a remote community in southern Sichuan, and why is it now declining? This thesis examines Naxi polyandry as a culturally transmitted adaptive strategy, shaped by ecological scarcity, kinship-based economic logics, and shifting pathways of cultural transmission. While polyandry has been documented across various Himalayan societies, the Naxi case differs significantly from the better-known models of their neighbors, the Tibetans and the Mosuo. Drawing on cultural evolutionary theory, household-centered analysis, and gender dynamics, this study investigates how this marriage system emerged, stabilized, and is now transforming in response to both external pressures and internal negotiations. Based on original ethnographic fieldwork in twelve households, including semi- structured interviews, spatial and ritual observations, and social media analysis, this research documents how polyandrous families achieve significant advantages over monogamous ones. They control larger landholdings, coordinate labor more effectively, and preserve estate continuity. These arrangements are not only materially efficient but also reproductively advantageous at the household level: polyandrous families average more children than monogamous ones, even as individual men often experience reduced reproductive outcomes. Women, by contrast, frequently gain modest advantages in reproductive success and household influence, benefiting from redistributed paternal investment and cooperative household structures. These findings position polyandry as a stable strategy that privileges collective welfare over individual maximization. Yet material advantages alone do not explain its persistence. Polyandry's viability has historically relied on integration into a broader cultural ecology that emerged through success-biased and prestige-biased transmission mechanisms, including permissive attitudes toward sexual flexibility, influence from neighboring Tibetan fraternal systems, and selective absorption of Confucian ideals that stress lineage continuity without mandating monogamy. These culturally transmitted features enabled the acceptance and normalization of polyandrous arrangements. Naxi households developed institutional mechanisms to manage internal tensions, such as strategic ambiguity around paternity, conjugal rotation embedded in architectural design, and Dongba ritual legitimation of marital forms. Today, these cultural foundations are weakening. As younger Naxi pursue education, digital entrepreneurship, and urban employment, they increasingly turn to Han Chinese models of autonomy and monogamy. While many still acknowledge polyandry's benefits, fewer choose it. Emerging hybrid arrangements, such as sequential polyandry, where brothers join the marriage over time, and distributed households, reflect active adaptation rather than cultural rupture. This thesis argues that Naxi polyandry is neither a cultural oddity nor an inexplicable vestige, but a contextually rational and culturally legitimated strategy. Its transformation exemplifies how marriage systems evolve through adaptive negotiation, balancing inherited logics with shifting aspirations.