Contagious yawning research conducted by Elainie Madsen, Tomas Persson and colleagues explained beautifully by The New York Times.
Read more about the research here!
The paper: Madsen, E. A., Persson, T., Sayehli, S., Lenninger, S., & Sonesson, G. (2013). Chimpanzees show a developmental increase in susceptibility to contagious yawning: A test of the effect of ontogeny and emotional closeness on yawn contagion. PloS one, 8(10), e76266. (Opens in new window)