Moya Cristina, Snopkowski Kristin, Sear Rebecca
Department of Human Evolutionary Biology, Harvard University, 11 Divinity Ave, Cambridge, MA 02138, USA
Department of Anthropology, Boise State University, 1910 University Drive, Boise, ID 83725, USA.
Philos Trans R Soc Lond B Biol Sci. 2016 Apr 19;371(1692):20150149. doi: 10.1098/rstb.2015.0149.
Several empirical observations suggest that when women have more autonomy over their reproductive decisions, fertility is lower. Some evolutionary theorists have interpreted this as evidence for sexual conflicts of interest, arguing that higher fertility is more adaptive for men than women. We suggest the assumptions underlying these arguments are problematic: assuming that women suffer higher costs of reproduction than men neglects the (different) costs of reproduction for men; the assumption that men can repartner is often false. We use simple models to illustrate that (i) menorwomen can prefer longer interbirth intervals (IBIs), (ii) if men can only partner with wives sequentially they may favour shorter IBIs than women, but such a strategy would only be optimal for a few men who can repartner. This suggests that an evolved universal male preference for higher fertility than women prefer is implausible and is unlikely to fully account for the empirical data. This further implies that if women have more reproductive autonomy, populations should grow, not decline. More precise theoretical explanations with clearly stated assumptions, and data that better address both ultimate fitness consequences and proximate psychological motivations, are needed to understand under which conditions sexual conflict over reproductive timing should arise.
一些实证观察表明，当女性在生育决策上拥有更多自主权时，生育率会更低。一些进化理论家将此解释为利益性冲突的证据，认为高生育率对男性比对女性更具适应性。我们认为这些论点背后的假设存在问题：假设女性承担的生育成本高于男性，忽视了男性（不同的）生育成本；男性可以再婚的假设往往是错误的。我们用简单模型说明：（i）男性或女性可能更喜欢更长的生育间隔（IBIs）；（ii）如果男性只能依次与妻子生育，他们可能比女性更喜欢较短的生育间隔，但这种策略只对少数能够再婚的男性才是最优的。这表明，进化出一种普遍的男性对高生育率的偏好高于女性的偏好是不合理的，也不太可能完全解释实证数据。这进一步意味着，如果女性有更多的生育自主权，人口应该增长，而不是减少。需要更精确的、有明确假设的理论解释，以及能更好地兼顾最终适应性后果和直接心理动机的数据，来理解在哪些情况下会出现生育时间上的性冲突。
