Kin Effects on Fertility. Evidence from Bejsce’s Parish Register Reconstitution Study: 18th-20th Century, Poland

Krzysztof Tymicki, Warsaw School of Economics

The standard biodemographic hypothesis states that individuals should enhance reproductive performance of their relatives. This hypothesis originates in the inclusive fitness theory, which predicts that kinsmen have genetic incentive to assist reproduction of biologically related individuals because such assistance indirectly contributes to their own reproductive performance. The paper aims to provide a partial verification of this hypothesis through estimation of the siblings’ effect on completed fertility and parity transition risks of women from the historical European population. The data are based on reconstitution of parish registers from Bejsce, located in south-central Poland for period 1740-1968. To estimate these effects, we have applied regression models for count outcomes and techniques event history analysis. We have found strong overall effect of siblings on fertility both in terms of the effect on completed fertility and parity specific transition risks. However, much weaker evidence supports hypothesis that siblings influence number of ego’s surviving offspring.