Imagine a yawn. You stretch your jaws open in a wide gape, take a deep inward breath, followed by a shorter exhalation, and end by closing your jaws. Ahhh. You have just joined vertebrates everywhere in one of the animal kingdom's most ancient rites. Mammals and most other animals with backbones yawn; fish, turtles, crocodiles and birds do it. People start yawning very early, offering further e...

Yawning is a phylogenetically old behaviour that can be observed in most vertebrate species from foetal stages to old age. The origin and function of this conspicuous phenomenon have been subject to speculations for centuries. Here, we review the experimental evidence for each of these hypotheses. It is found that theories ascribing a physiological role to yawning (such as the respiratory, arou...

The biomedical hypothesis proposed here is that the immediate trigger for a yawn is a restricted collapse of a few alveoli in the lungs. The extent of this alveolar collapse may be too small for it to be detected by current X-ray technology, but this technology is continually improving and may soon be good enough to test the hypothesis. In support of the hypothesis, it is shown that yawning can...

BACKGROUND Although some research suggests that fetuses yawn, others disagree arguing that is it simple mouth opening. Furthermore there is no developmental account of fetal yawning compared with simple mouth opening. The aim of the present study was to establish in a repeated measures design the development of fetal yawning compared with simple mouth opening. METHODOLOGY/FINDINGS Video recor...

On the basis of observational and experimental evidence, several authors have proposed that contagious yawn is linked to our capacity for empathy, thus presenting a powerful tool to explore the root of empathy in animal evolution. The evidence for the occurrence of contagious yawning and its link to empathy, however, is meagre outside primates and only recently domestic dogs have demonstrated t...

Contagious yawning, in which yawning is triggered involuntarily when we observe another person yawn, is a common form of echophenomena-the automatic imitation of another's words (echolalia) or actions (echopraxia) [1]. The neural basis for echophenomena is unknown; however, it has been proposed that it is linked to disinhibition of the human mirror-neuron system [1-4] and hyper-excitability of ...

While comparative research on contagious yawning has grown substantially in the past few years, both the interpersonal factors influencing this response and the sensory modalities involved in its activation in humans remain relatively unknown. Extending upon previous studies showing various in-group and status effects in non-human great apes, we performed an initial study to investigate how the...