Trixillini's LaLaLand: Why is yawning contagious

Been yawning so much our whole lives but i never figured what is the ACTUAL purpose (besides wanting to sleep) and why it is contagious..so i did some reading and found:

1) Yawning is designed to keep us awake

2) Most creatures on earth yawns, even fishes & snakies, dogs, hippos (apparently dogs yawn to stay calm in certain situations!!) Poor Yuki must be very nervous everyday!!hahah..

3) Rather than being a precursor to sleep, the purpose is to cool the brain so it can operate more efficiently and keep you awake.

4) It's been suggested contagious yawning could be a result of an unconscious herding behaviour - a subtle way to communicate to those around us, similar to when flocks of birds take flight at the same time.

5) Contagious yawning might have helped early humans communicate their alertness levels and co-ordinate sleeping times. Basically, if one decided it was time to sleep they would tell the others by yawning and they would do it in return to show they agreed

6) The "Brain Cooling Theory" says that when we contagiously yawn, we are participating in an ancient, hardwired ritual that evolved to help groups stay alert and detect danger

7) Chimpanzees are the only other creatures that suffer from contagious yawning, next to humans..