Women's Position in Ancestral Societies and Female HIV: The Long-Term Effect of Matrilineality in Sub-Saharan Africa

Can contemporary female HIV rates be traced back to women's position in ancestral societies? In matrilineal kinship organizations, lineage and inheritance are traced through female members, granting women historically greater agency while reducing the structural stability of the marital bond. This paper tests the hypothesis that ancestral matrilineality, by shaping women's sexual and contraceptive behaviors, significantly impacts the prevalence of female HIV today. By exploiting individual-level variation in ethnic identity across 18 countries, and using granular region-survey fixed effects, I find that women from ancestrally matrilineal ethnic groups face a significantly higher probability of being HIV-positive. This \enquote{matrilineal penalty} is confirmed by a geographic regression discontinuity design (RDD) at ethnic boundaries, ensuring the results reflect persistent social structures rather than geographic confounders. I identify three primary behavioral mechanisms: (i) increased female agency leading to greater sexual mobility and marital turnover; (ii) a coordination failure within the couple regarding condom use due to the fragility of the marital bond; and (iii) biological evidence from couple sero-discordance showing that the virus primarily enters the household through the female partner. These results suggest that female agency, in the absence of formal diagnostic information, may increase vulnerability to health shocks. My findings call for public health policies that prioritize routine HIV testing to bridge the information gap and convert latent ancestral agency into active health protection.