Contrary to spontaneous yawning, which is widespread in vertebrates and probably evolutionary ancient, contagious yawning—yawning triggered by others’ yawns—is considered an evolutionarily recent phenomenon, found in species characterized by complex sociality. Whether the social asymmetry observed in the occurrence of contagious yawning is related to social and emotional attachment and may therefore reflect emotional contagion is a subject of debate. In this study we assessed whether yawn contagion was enhanced in pregnant women, a cohort of subjects who develop prenatal emotional attachment in preparation for parental care, via hormonal and neurobiological changes. We predicted that if yawn contagion underlies social and emotional attachment, pregnant women would be more likely to contagiously yawn than nonpregnant, nulliparous women of reproductive age. We gathered data in two different settings. In the experimental setting, 49 women were exposed to video stimuli of newborns either yawning or moving their mouth (control) and we video-recorded the women during repeated trials to measure their yawning response. In the naturalistic setting, 131 women were observed in a social environment and their yawning response was recorded. We tested the factors influencing the yawning response, including the reproductive status (pregnant vs. not pregnant). In both settings, yawn contagion occurred significantly more in pregnant than nonpregnant women. By showing that pregnant women were most likely to respond to others’ yawns, our results support the hypothesis that the social variation observed in yawn contagion may be influenced by emotional attachment and that yawning in highly social species might have been coopted for emotional contagion during evolution.

与自发性打哈欠相反，自发性打哈欠在脊椎动物中普遍存在，并且可能是进化上古老的，传染性打哈欠——由其他人的打哈欠引发的打哈欠——被认为是一种进化上最近出现的现象，在具有复杂社会性特征的物种中发现。在传染性打哈欠的发生中观察到的社会不对称是否与社会和情感依恋有关，因此可能反映情绪传染是一个有争议的话题。在这项研究中，我们评估了孕妇打哈欠的传染性是否增强，这是一组通过荷尔蒙和神经生物学变化而产生产前情感依恋以准备父母照顾的受试者。我们预测，如果打哈欠传染是社会和情感依恋的基础，那么孕妇比未怀孕的妇女更有可能传染性打哈欠，育龄未生育妇女。我们在两种不同的环境中收集数据。在实验环境中，49 名妇女暴露于新生儿打哈欠或移动嘴巴（对照）的视频刺激下，我们在反复试验中对这些妇女进行了视频记录，以测量她们的打哈欠反应。在自然环境中，131 名女性在社会环境中被观察并记录了她们打哈欠的反应。我们测试了影响打哈欠反应的因素，包括生殖状态（怀孕与未怀孕）。在这两种情况下，孕妇比非孕妇更容易感染哈欠。通过表明孕妇最有可能对别人的哈欠做出反应，