SummaryWe tested the proposition that among humans (1) differences in lactational duration result in differences in costs of reproduction even under rich nutritional conditions; and (2) elimination of factors postulated to favor male-biased parental care will be reflected in elimination or reversal of sex-biased care. To do so, we examined the relationship between lactational duration and fertility among Hutterites, a communal-living human population in which the levels of nutritional resources and fertility are high, breast-feeding is the norm, contraceptive use is limited and the collective social and economic system results in low resource variance among individuals. We demonstrate that even under good nutritional conditions, duration of nursing was a significant predictor of the length of time to next pregnancy and that nursing continued to suppress fertility after the resumption of menses. Moreover, we find that daughters were nursed longer than sons, leading to a longer interval to next pregnancy. We examine this uncommon, but not unique, finding of female-biased human parental care in the light of Hutterite social structure, and we explore the consistency of this finding with the most applicable models of parental investment.

中文翻译：

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人口中性别偏向的哺乳期及其生殖成本

总结我们测试了以下命题：(1) 即使在营养丰富的条件下，泌乳持续时间的差异也会导致繁殖成本的差异；(2) 消除假定有利于男性偏见的父母照顾的因素将反映在消除或逆转性别偏见的照顾上。为此，我们研究了 Hutterites 的哺乳期持续时间与生育率之间的关系，Hutterites 是一个社区生活的人群，其中营养资源和生育率水平很高，母乳喂养是常态，避孕药具的使用有限，集体社会和经济系统导致个体之间的资源差异很小。我们证明，即使在良好的营养条件下，哺乳时间是下次怀孕时间长度的重要预测因素，并且在月经恢复后哺乳继续抑制生育能力。此外，我们发现女儿的哺乳时间比儿子长，导致下一次怀孕的间隔时间更长。我们根据哈特派的社会结构研究了这种不常见但并非独特的女性偏见人类父母照料的发现，并探讨了这一发现与最适用的父母投资模型的一致性。