Difference in contagious yawning between susceptible men and women: why not?

In their commentary, Gallup & Massen [1] criticize the fact that we did not consider ‘more than a dozen’ previous publications which did not report gender differences in human contagious yawning. We thank the authors for pointing out this issue and for giving us the possibility to provide a brief explanation on some aspects that are not as obvious as we thought. Our investigation was ethological and our framework was centred on behavioural studies also on non-human primates and other mammals. We therefore selected the articles that were relevant to our comparative and evolutionary approach. Gallup & Massen [1] state that the gender difference in yawn contagion detected in our study is a false positive and that the null effect is real. Unfortunately, the sample that they used to make this assumption (17 negative cases and one positive case) is incorrect and, consequently, so is their conclusion. The possibility to find a phenomenon relies on whether the sample and the methodology used are suitable to detect it. To retain the metaphor used by Gallup & Massen [1], you can flip a coin as many times as you want and never find what you expect if what you expect is to get a six. You should change the approach and roll a dice, instead. The results presented in the article by Palagi et al. [2] were based on naturalistic observations (and not on videos as it is said in table 1 of the commentary [1]) and the database also included bonobos, in which the sex of the trigger and not the sex of the responder tended to influence yawn contagion rates [3]. Therefore, it could not be used to evaluate which variables affect yawn contagion rates in humans only. Four of the articles mentioned in their commentary must be excluded from the sample, because they were focused on sexually immature subjects and on the difference between autistic versus non-autistic children [4–7], whereas our study was focused on non-pathological adults. Children are not suitable to test for gender differences because the power of empathy and yawn contagion is strongly influenced by age [8]. One further article cannot be included because the