Three questions to do with yawning.?

Question

When you are with a group of people and one person yawns the yawn becomes almost contagious, but is it to do with seeing someone else yawn (if so why is it triggered by sight) or is it possibly to do with some sort of chemical (perhaps "chemical" is the wrong word, but some sort of change in the air you breathe") released when yawning?

Why do people yawn? I've heard many times that it's to do with lack of oxygen but after exercise probably the time when you have the least oxygen I don't seem to yawn. Is it true?

What is the purpose of yawning/does it benefit us?

Thanks very much.

Answer 1

The usual answer is that yawning is to rid the body of excess carbon dioxide, which is somewhat different from replacing deficient oxygen.  As to why it's contagious, I think that has already been answered well.

Answer 2

Contagious yawning seems to be an empathic response. Autistic people don't seem to be affected by this.

Yawning occurs when a sudden oxygen decrease happens, and our bodies are not normally aware of it. The yawn replenishes our oxygen levels. After exercise, we usually pant, and our bodies are aware of the energy/oxygen difference, so there is no reflex to trigger breathing.

Yawning is a reflex. It occurs when we need a sudden burst of oxygen or are in need of energy.