Originally Posted by ebus_dk

Its part of the subconscious of almost all animals and human (the flock animals)
It goes back to the time where we were nomads traveling from hunting ground to hunting ground. If one got tired, and therefore Yawned, it spread to the whole flock, so everybody stopped, and no-one was left behind.

If you study the lions in Africa, it is very very obvious there as well.. as soon as one starts, the rest follows just like humans.. and they rest before going further.
that way no members is lost from the pack, and the pack stay strong