Why did many systems of primogeniture favor sons over daughters?

Systems of primogeniture favored sons over daughters primarily to keep estates, titles, and political power intact and within a specific lineage. By designating a single heir—traditionally the eldest son—aristocratic families prevented the partitioning of land into parcels too small to maintain their status, wealth, and influence.12

In many monarchical and noble systems, this practice was reinforced by legal frameworks such as the Salic Law of Succession, which explicitly excluded women from inheriting the throne to ensure the continuity of the dynasty through the male line. While some cultures allowed for female succession in the absence of male heirs, these women were often viewed as "heirs presumptive" whose claims could be superseded by the birth of a son.32

Historically, these practices were justified by custom, perceived religious or legal traditions, and the desire to preserve the prestige of the aristocracy. However, modern systems have increasingly moved toward "absolute primogeniture," which favors the eldest child regardless of gender, reflecting a shift toward principles of equality.132