Why are yawns so contagious?

Helen - I think you share a trait between about 40 and 60% of people who find yawns very catchable. The answer is we don't know. We don't really know why it is that yawns are so contagious. I think we're not even quite sure why we yawn anyway! There's lots of ideas as to what that is. We're not alone in our catching of yawns. Chimpanzees do it as well and it's an unconscious process so we really don't know what it is. It could be early on in evolution we needed to communicate how sleepy we were because it was important for groups of people to go to sleep at the same time and wake up at the same time. Things like that. By yawning it created a synchronised behaviour and that sort of thing. That could be a reason why. People have actually looked at what's going on inside our brains when we are catching yawns by putting people inside of magnetic resonance machines and looking at patterns of electricity inside your brain when you're watching other people yawn. It hasn't really opened up much of an answer to what's going on. We get a lowering in activity of a particular part of the brain called the peri-amygdala region. This is deactivated very strongly if you have a person who really wants to yawn. The desire to yawn varies between different people. We're really left with a bit of a question mark on that one.

Although I did rather love some experiments I found a report of which is at a zoo - They wanted to see if this was cross-species so they went round with people looking at animals yawning to see if it made us yawn. And seeing also if we could make animals yawn by yawning at them. Unfortunately the answer is no. Someone claimed they caught a yawn from a lion but I don't know if that really counts!

Chris - I feel a little bit like yawning with my pets. I have a pet dog and when that yawned I would feel the inclination.

Helen - It's possible. It's a very peculiar thing because it's not about an open mouth. If you cover up a yawn it's still contagious. It seems people are more self-aware and empathetic. It's something to do with imagining how that other person you're looking at is feeling. We begin yawning in the womb. We don't know enough about it and why it happens but it's a very good question. Keep working on it until we find out. Chris - There's a researcher in New York called Gordon Gallup who did some work on yawns. He showed students videos of people yawning and looked at who yawned in sympathy. He then did two things. He asked the students to breathe through their noses or to breathe with their mouths open or hold a cold compress on their forehead. Both these strategies, when you hold a cold compress or breathe through the mouth you can affect yawning. If you breathe through the mouth you yawn more; if you hold a cold compress on your head you yawn less.

His theory is that yawning cools the brain in some way. It's to do with alertness. If you have an infectious yawning behaviour, if you have a group of people who are all sitting round a campfire at night and there's a danger some predator might come along - if one person starts yawning it means one person's getting a little on the tired side. By cooling the brain and increasing alertness - when you have sleep deprivation brain temperature rises - this means if everyone catches the yawn everyone is made more alert at once. This keeps everyone looking for any danger. This is his theory.