Contagious yawning differs from spontaneous yawning because it occurs when an
individual yawns in response to someone else’s yawn. In Homo sapiens and some nonhuman
primates contagious yawning is higher between strongly than weakly bonded
individuals. Up to date, it is still unclear whether this social asymmetry underlies
emotional contagion (a basic form of empathy preferentially involving familiar individuals)
as predicted by the Emotional Bias Hypothesis (EBH) or is linked to a top-down,
selective visual attention bias (with selective attention being preferentially directed toward
familiar faces) as predicted by the Attentional Bias Hypothesis (ABH). To verify whether
the visual attentional bias explained the yawn contagion bias or not, in this study,
we considered only yawns that could be heard but not seen by potential responders
(auditory yawns). Around 294 of auditory yawning occurrences were extrapolated from
over 2000 yawning bouts collected in free ranging humans for over nine years. Via
GLMM, we tested the effect of intrinsic features (i.e., gender and age) and social bond
(from strangers to family members) on yawn. The individual identity of the subjects
(trigger and potential responder) was included as random factor. The social bond
significantly predicted the occurrence of auditory yawn contagion, which was highest
between friends and family members. A gender bias was also observed, with women
responding most frequently to others’ yawns and men being responded to most
frequently by others. These results confirm that social bond is per se one of the main
drivers of the differences in yawn contagion rates between individuals in support of the
EBH of yawn contagion