Yawning Is More Contagious in Pregnant Than Nulliparous Women : Naturalistic and Experimental Evidence

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.

Keywords: Emotional contagion; Empathy evolution; Maternal–fetal attachment; Prenatal attachment.

Fig. 1

Screenshots from the experimental video showing the control condition (top: babies moving their mouths) and the yawning condition (bottom)

Fig. 2

Effect of the type of the video condition (yawning/control) on the yawning response (experimental setting). Line plot showing the yawning response (Y axis) in the experimental setting as a function of the condition (yawning/control; X axis). The presence of a yawning response was significantly more likely in the yawning (M = 0.3322; SE = 0.039) than in the control (M = 0.120; SE = 0.026) condition (statistical results: Table 1), which confirms the presence of yawn contagion. Mean (circle) and 95% confidence interval (bars) are indicated

Fig. 3

Effect of the reproductive status on the yawning response (experimental setting). Line plot showing the yawning response (Y axis) in the experimental setting as a function of the reproductive status of the woman potential responder (nulliparous/pregnant; X axis). The presence of a yawning response in the yawning video condition was significantly more likely (M = 0.416; SE = 0.057) in pregnant than in nulliparous (M = 0.217; SE = 0.050) women (Statistical results: Table 2). Mean (circle) and 95% confidence interval (bars) are indicated

Fig. 4

Effect of the social bond on the yawning response (naturalistic setting). Line plot showing the yawning response (Y axis) in the naturalistic setting as a function of social bond between trigger and potential responder (strangers/acquaintances; X axis). The presence of a yawning response was significantly more likely between acquaintances (Mean ± SE: 0.168 ± 0.031) than between strangers (M = 0.164; SE = 0.029) (statistical results: Table 3). Mean (circle) and 95% confidence interval (bars) are indicated

Fig. 5

Effect of the reproductive status on the yawning response (naturalistic setting). Line plot showing the yawning response (Y axis) in the naturalistic setting as a function of the reproductive status of the woman potential responder (nulliparous/pregnant; X axis). The presence of a yawning response was significantly more likely in pregnant (M = 0.225; SE = 0.036) than in nulliparous (M = 0.118; SE = 0.025) women (statistical results: Table 3). Mean (circle) and 95% confidence interval (bars) are indicated