There is no difference in contagious yawning between men and women

Norscia et al. [1] recently reported the first evidence for a sex bias in contagious yawning among humans. Based on previous research showing an indirect connection between contagious yawning and empathy (e.g. [2–4], but see [5,6]) and that levels of empathy appear to be higher in women compared with men (e.g. [7–9]), the authors investigated whether there is also a sex difference in the expression of contagious yawning through an observational study on humans. By examining 92 dyads already showing evidence of contagious yawning, which was a subset of a much larger sample of individuals, Norscia et al. report that both social bond and sex were significant predictors of this response. In particular, contagious yawning was more common if the dyad was strongly bonded and when the individual catching the yawn was female. Here, we call into question these conclusions about a sex difference in contagious yawning. First, we draw attention to more than a dozen previous publications on contagious yawning in humans, many of which were not cited by Norscia et al. showing no difference in susceptibility to yawn contagiously and/or contagious yawning frequency between men and women. Similarly, we do the same for nearly a dozen unacknowledged publications in the comparative literature. Lastly, we challenge the validity of the reported sex difference within the Norscia et al. study itself, based on their analysis of only a restricted subset of documented contagious yawners. A close examination of the empirical literature clearly shows that the sex difference reported by Norscia et al. stands in stark contrast to previous findings on contagious yawning in humans. While Norscia et al. only reference a single publication that did not find a difference in the frequency of contagious yawning between men and women [5], we provide references to an additional 14 papers showing no effect (two of which were in fact written by some of the Norscia et al. authors in question; table 1).