Abstract: This paper studies the influence of marine ecology on social institutions of inheritance and descent. In a sample of 79 small-scale horticultural fishing communities in the Solomon Islands, and in samples of 186 to 1,265 societies across the world, we find that coral reef density systematically predicts the prevalence of matrilineal inheritance. Moreover, this result likely reflects adaptation of institutions to ecological conditions, as it holds within ethno-linguistic groups. Reef density explains as much as 10\% of the variation in inheritance rules across villages in the Solomon Islands. Explanations based on the sexual division of labor and on inclusive fitness arguments support our results. We also document some of the demographic consequences of matrilineal inheritance, including smaller household and village population size, but find at best weak evidence that matrilineal inheritance translates into higher female economic or political agency.