The research, presented at the British Association's Festival of Science in York, suggests that while almost all animals with a backbone yawn, the reflex is only infectious among humans, chimpanzees and some monkeys, and contagious yawning is thought to have evolved as a means of social communication.
"Contagious yawning is a very interesting behaviour," BBC quoted Dr Catriona Morrison, a lecture in psychology at the University of Leeds, who is leading the work.
"You don't need a visual cue, you don't even need an auditory cue - you can just read about it or think about it and it gets you going. We believe that contagious yawning indicates empathy. It indicates an appreciation of other people's behavioural and physiological state," she added.
Recent neuro-imaging has shown that the same area of the brain is involved when reacting to yawning and when considering others. Dr Morrison tested the theory on students of psychology and engineering. Each student was shown to an occupied waiting room where their companion was actually a researcher who yawned 10 times in 10 minutes. The scientists recorded how often the students yawned in response.
Each participant was then asked to complete a test of their empathetic skills, in which they analysed pictures of eyes and recorded the emotions shown.
On average, the psychology students yawned 5.5 times, compared with 1.5 yawns for the engineers in the first experiment, and in a subsequent one, the average score was 28 for the psychologists and 25.5 for the engineers.
This suggests that the psychology students were more susceptible to contagious yawning, and scored significantly higher on the empathy test than did the engineering students. "We thought that psychology students would be highly empathetic and that engineering students would be more systemised, more interested in numbers and formulas," Morrison said.
She added that yawning, which is often related to tiredness, may have evolved as a way of improving alertness in social groups.