Do only mammals yawn? And why do we have to yawn when we see someone else yawn?

Question

Even when I see my dog yawn, I have to yawn!

But when he sees me yawn, he doesn't!

Answer 1

From Wikipedia:

"A previous long-standing hypothesis is that yawning is caused by an excess of carbon dioxide and lack of oxygen in the blood. The brain stem detects this and triggers the yawn reflex. The mouth stretches wide and the lungs inhale deeply, bringing oxygen into the lungs and hence to the bloodstream. It is almost certain, however, that this hypothesis is not correct. One study has documented that this effect does not exist."

Goes on to newer, updated theories.

Also:

"The reasons for this are unclear; however, recent research suggests that yawning might be a herd instinct. Other theories suggest that the yawn serves to synchronize mood behavior among gregarious animals, similar to the howling of the wolf pack during a full moon."

Goes on to give other reasons for contagion. Enough!

Answer 2

I've seen birds & reptiles yawn. As for why we feel the need to yawn when someone else yawns, I have no idea.

Answer 3

i do not know if only mammals yawn but i know that yawning is contagious so we yawn after seeing someone yawn.

Answer 4

we yawn because of oxygen deficiency and why we yawn when we see someone else yawn is because its a reflex action.

i believe plants yawn too....