Postpartum amenorrhea (PA) affects the length of interbirth intervals and thus is intimately related to human life history strategies. PA duration appears to be influenced by maternal energetic status. In humans, as in other mammals, sons are costlier than daughters. Thus, we hypothesize that, in energetically constrained environments, a newborn's sex should be associated with PA duration.

中文翻译：

---

两个自然生育人群中按性别划分的产后闭经持续时间

产后闭经（PA）影响分娩间隔的时间，因此与人类生活史策略密切相关。PA的持续时间似乎受孕产妇精力充沛状态的影响。在人类中，就像在其他哺乳动物中一样，儿子比女儿昂贵。因此，我们假设在能量受限的环境中，新生儿的性别应与PA持续时间相关。