标题： 平衡最后一次生育：人类性别比例谜题的博弈论解决方法 显示英文标题

标题： Balancing the Last Birth: A Game-Theoretical Resolution to the Human Sex Ratio Puzzle

摘要： 我们使用一个博弈论模型来研究后代性别比例的变化，其中决定是否再生育一个孩子取决于前一个孩子的性别。 受男性婴儿死亡率较高以及在孩子去世后倾向于再次尝试的倾向启发，我们的模型允许在儿子和女儿之后有不同的继续生育概率。 我们发现，当这些继续生育概率不同时，出生时的性别比例（SRB）可以稳定地偏离1:1。 然而，最后出生的儿童性别比例（SRLB）总是趋近于1:1。 我们数学证明了这种1:1的SRLB在基于成功交配对中的后代数量而非整个种群中的后代数量的新适应度衡量标准下是一种进化上稳定的策略。 我们的结果通过表明即使整体SRB存在偏差，平衡仍可在最后生育水平上维持，从而推广了费舍尔原则。 这为人类出生中持续存在的轻微男性偏差提供了一个可能的解释，将其与特定性别的儿童死亡率以及历史人口中的父母繁殖策略联系起来。 显示英文摘要

摘要： We study the evolution of offspring sex ratios using a game-theoretical model in which the decision to have another child depends on the sex of the previous child. Motivated by higher male infant mortality and the tendency to try again after a child's death, our model allows different continuation probabilities after sons and daughters. We find that a stable sex ratio at birth (SRB) differing from 1:1 can arise when these continuation probabilities differ. However, the sex ratio among last-born children (SRLB) always converges to 1:1. We mathematically prove that this 1:1 SRLB is an evolutionarily stable strategy under a new fitness measure based on the number of offspring in successful mating pairs, rather than the number of descendants in the whole population. Our results generalize Fisher's principle by showing that equilibrium is maintained at the level of last births even when the overall SRB is biased. This offers a potential explanation for the persistent slight male bias in human births, linking it to sex-specific child mortality and parental reproductive strategies in historical populations.