Taking a break from weighty stuff like finding a cure for cancer and the like, scientists have discovered that dogs, jus tlike humans, find yawns contagious:
A team from Birkbeck College at the University of London wanted to know whether canines - known to be highly skilled at reading human social cues - could read the human yawn signal, reports the BBC.
The team found that 21 out of 29 dogs yawned when the stranger in front of them had first. By contrast, no dogs yawned during the test where the person did not yawn.
Perhaps humans did it for the same reason once, long ago, and the visceral memory remains.