Abstract
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.
Highlights
IntroductionWhereas spontaneous yawning is independent from the perception of others’ yawns, contagious yawning occurs when the yawn emitted by a subject (trigger) acts as a releasing stimulus (sensu Tinbergen and Perdeck 1951) and elicits yawning in another subject (responder) (Provine 1989)
Whereas spontaneous yawning is independent from the perception of others’ yawns, contagious yawning occurs when the yawn emitted by a subject acts as a releasing stimulus and elicits yawning in another subject (Provine 1989)
Morphological variants are present in yawns, especially in primates, spontaneous yawning is probably a plesiomorphic trait because it has been recorded in a wide array of vertebrates (Baenninger 1987)
Summary
Whereas spontaneous yawning is independent from the perception of others’ yawns, contagious yawning occurs when the yawn emitted by a subject (trigger) acts as a releasing stimulus (sensu Tinbergen and Perdeck 1951) and elicits yawning in another subject (responder) (Provine 1989). It has been hypothesized that in highly social species yawning may have been coopted during evolution for emotional contagion, a basic building block of empathy (de Waal and Preston 2017; Palagi et al 2020) At present, it is highly debated for both human and nonhuman animals whether the social asymmetry observed in yawn contagion depends on interindividual bonding, possibly reflecting emotional attachment—as postulated by the Emotional Bias Hypothesis (EBH)—and/or on other factors, such as attentional levels, social dominance, or as-yet undefined aspects of the social setting (Adriaense et al 2020; Kapitány and Nielsen 2017; Massen and Gallup 2017; Palagi et al 2020). These changes often alter body systems so that pregnant women perform and act differently (e.g., with respect to dietary choice, motor activity, sensitivity to emotional stimuli) than nonpregnant women in the general population (Crozier et al 2009; Gradmark et al 2011; Moya et al 2014; Osório et al 2018)
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