A Novel Quantitative Approach to Women’s Reproductive Strategies

The patterned way in which individuals allocate finite resources to various components of reproduction (e.g. mating effort, reproductive timing and parental investment) is described as a reproductive strategy. As energy is limited, trade-offs between and within aspects of reproductive strategies are expected. The first aim of this study was to derive aspects of reproductive strategies using complete reproductive histories from 718 parous Western Australian women. Factor analysis using a subset of these participants resulted in six factors that represented ‘short-term mating strategy’, ‘early onset of sexual activity’, ‘reproductive output’, ‘timing of childbearing’, ‘breastfeeding’, and ‘child spacing’. This factor structure was internally validated by replication using a second independent subset of the data. The second aim of this study examined trade-offs between aspects of reproductive strategies derived from aim one. Factor scores calculated for each woman were incorporated in generalised linear models and interaction terms were employed to examine the effect of mating behaviour on the relationships between reproductive timing, parental investment and overall reproductive success. Early sexual activity correlates with early reproductive onset for women displaying more long-term mating strategies. Women with more short-term mating strategies exhibit a trade-off between child quantity and child quality not observed in women with a long-term mating strategy. However, women with a short-term mating strategy who delay reproductive timing exhibit levels of parental investment (measured as breastfeeding duration per child) similar to that of women with long-term mating strategies. Reproductive delay has fitness costs (fewer births) for women displaying more short-term mating strategies. We provide empirical evidence that reproductive histories of contemporary women reflect aspects of reproductive strategies, and associations between these strategic elements, as predicted from life history theory.

个体将有限资源分配至繁殖活动各环节（如求偶投入、繁殖时机与亲代抚育投入）的模式化路径，被定义为繁殖策略（reproductive strategy）。鉴于能量资源有限，繁殖策略各维度内部及维度之间均存在权衡关系。本研究的首要目标是，基于718名经产西澳女性的完整生育史，推导繁殖策略的各维度构成。通过对其中一部分受试者开展因子分析，最终提取出六个因子，分别对应短期择偶策略（short-term mating strategy）、性活动起始年龄偏早、生育总量、生育时机、母乳喂养以及生育间隔。通过第二份独立的受试者子数据集进行重复验证，该因子结构的内部效度得到确认。本研究的第二目标旨在探讨由首要目标推导得到的繁殖策略各维度之间的权衡关系。为每位女性计算得到的因子得分被纳入广义线性模型（generalised linear models），同时引入交互项以探究择偶行为对生育时机、亲代抚育投入与整体繁殖成功率之间关联的调控效应。对于采用长期择偶策略（long-term mating strategy）的女性而言，较早的性活动起始年龄与更早的生育启动时间呈显著正相关。采用短期择偶策略的女性会表现出子代数量与子代质量之间的权衡关系，而这一现象在采用长期择偶策略的女性中并未观测到。然而，延迟生育时机的短期择偶策略女性，其亲代抚育投入水平（以每名子女的母乳喂养时长衡量）与长期择偶策略女性相当。对于采用短期择偶策略的女性而言，延迟生育会带来适合度代价（即生育子代数量减少）。本研究提供了实证证据，表明当代女性的生育史能够反映其繁殖策略的各维度构成，且这些策略维度间的关联符合生活史理论（life history theory）的预测。