Effects of female reproductive competition on birth rate and reproductive scheduling in a historical human population

Costly reproductive competition among females is predicted to lead to strategies that reduce these costs, such as reproductive schedules. Simultaneous births of co-resident women in human families can reduce their infant survival, but whether such competition also affects overall birth rates and whether females time their pregnancies to avoid simultaneous births remain unknown, despite being key questions for understanding how intra-female competition affects reproductive strategies. Here, we used detailed parish registers to study female reproductive competition in historical Finnish joint –families, where brothers stayed on their natal farms and sisters married out, and consequently unrelated daughters-in-law often co-resided and competed for household resources. We quantified the time-varying effects of having reproductive-aged competitor(s) on a woman’s interval from marriage to first childbirth, on age-specific fertility, and on birth scheduling. Contrary to our hypothesis, the pre...雌性间代价高昂的生殖竞争，被预测会催生旨在降低此类成本的策略，例如生育时序规划。人类家庭中共住女性的同时生育，会降低其婴儿存活率，但此类竞争是否也会影响整体生育率，以及女性是否会通过调整怀孕时机以避免同时生育，仍是未解之谜——尽管这些问题是理解雌性内部竞争如何影响生殖策略的核心议题。本研究借助详尽的教区登记册，对历史芬兰联合家庭中的雌性生殖竞争展开研究：此类家庭中兄弟留守出生地农场，姐妹外嫁，因此无亲缘关系的儿媳往往会同住一处，并为家庭资源展开竞争。我们量化了存在生育年龄竞争者对女性从结婚至首胎生育间隔、年龄别生育率以及生育时序安排的时变效应。与我们的假说相悖，此前的……