The Association between Pro-Social Attitude and Reproductive Success Differs between Men and Women

The evolution of pro-social attitude and cooperation in humans is under debate. Most of the knowledge on human cooperation results from laboratory experiments and theoretic modeling. Evolutionary explanations, however, rest upon fitness consequences. We therefore examined fitness correlates of pro-social behavior in a real life setting, analyzing data from the Wisconsin Longitudinal Study (n = 2545 men, 2967 women). We investigated whether pro-social attitude, proxied by self reported voluntary work, is associated with lifetime reproductive success. We find a sex difference in the association between pro-social attitude and offspring number. In men, a pro-social attitude was associated with higher offspring number, whereas in women, it was associated with lower offspring count. To our knowledge, this is the first study to demonstrate fitness consequences of pro-social behavior towards strangers. We conclude that analysing real life settings may help to explain the evolutionary forces leading to pro-social behavior in humans and speculate that these factors might differ between the sexes.人类亲社会态度与合作行为的演化机制目前尚存争议。当前关于人类合作的认知大多源自实验室实验与理论建模。然而，演化层面的解释均基于适合度（fitness）后果。因此，本研究在真实生活场景中考察了亲社会行为（pro-social behavior）与适合度的相关性，分析了威斯康星纵向研究（Wisconsin Longitudinal Study, WLS）的数据，样本包含男性2545人、女性2967人。本研究探讨了以自我报告的志愿工作作为代理指标的亲社会态度（pro-social attitude）是否与终身繁殖成功率存在关联。结果发现，亲社会态度与子女数量之间的关联存在性别差异：男性群体中，亲社会态度与更高的子女数量呈正相关；而女性群体中，二者则呈负相关。据我们所知，本研究首次证实了针对陌生人的亲社会行为所带来的适合度后果。本研究结论认为，对真实生活场景的分析有助于阐明驱动人类亲社会行为演化的进化动力，并推测这类进化动力在两性之间可能存在差异。