Does the sex of firstborn children influence subsequent fertility behavior? evidence from family reconstitution.

According to recent studies in evolutionary anthropology, firstborn daughters influence both parity progression and sibling survival by acting as so-called helpers at the nest. Based on 534 sets of household data from family reconstitution, the current analysis fails to show that offspring sex had any direct impact on maternal fertility, sibling survivorship, birth spacing, or reproductive span. Instead, the results indicate that fertility decisions were heavily affected by proximate factors such as child mortality and gender preferences. Families who had experienced child death were swift to substitute the loss with another pregnancy--a phenomenon known as replacement strategy. Similarly, a surplus of daughters acted as a strong impulse for parity progression, not because of potential helping effects but in an attempt to conceive additional sons. This is particularly apparent when the odds of grandmultiparity are considered.