Kin influence on female reproductive behavior: the evidence from reconstitution of the Bejsce parish registers, 18th to 20th centuries, Poland.

The phenomenon of kin-oriented help, according to inclusive fitness theory, should be of crucial importance with respect to the process of reproduction. This is due to the fact that the devoted time and resources might indirectly contribute to the reproductive performance of a donor. This study aimed at analyzing the kin effects on fertility in order to check whether help received from kinsmen enhance a recipient's reproduction in terms of parity transition risk, completed fertility, and the number of survivors. The data came from reconstitution of church registers from Bejsce parish, Poland. To estimate the kin effect, regression models for count outcomes and techniques of multilevel event history analysis were applied. The analyses have shown that completed fertility and parity-specific transition risks are strongly influenced by various kin groups. Moreover, a multilevel hazard model revealed differences in the patterns of the kin influence among controlled fertility than among natural fertility birth cohorts. Female reproductive outcome is influenced mainly by the presence of siblings and postreproductive helpers (grandparents). However, there is a negative impact of so-called helpers-at-the-nest (older children in the household) on parity transition risks.