Why can't we tickle ourselves?
Why can't we tickle ourselves? – Florence, aged 12, Cambridgeshire, UK.
Thanks for the question, Florence. The short answer is, we humans can't tickle ourselves because we'll already be expecting it. And a big part of what makes tickles ticklish is the element of surprise.
Tickling is an important sign that someone or something is touching you. In general, there are two types of tickles. There are good tickles, like when your family or friends tickle you and make you laugh. And there are bad tickles, like when you can feel a bug on you.
Both types of tickles help us in different ways.
Over the hundreds of thousands of years that humans have been around, being ticklish has had its advantages. Tickling tells us when there is a bug or something else crawling on our skin.
The reason why we feel ticklish is because our body is covered in small hairs. These help us to feel danger that might be too small to see – like bugs.
People who are ticklish can feel bugs land on them, and flick them off before they bite. This helps to avoid getting bitten by poisonous insects.
Over the ages, ticklish people would have been less likely to be bitten by poisonous bugs, so they would have lived longer and had more babies, who were also ticklish.
In other words, humans have evolved to be ticklish, because it can help us to sense danger, such as bugs. If we could tickle ourselves, then we might have more trouble telling when there's a bug on us or when we are just touching ourselves.
So it makes sense that we cannot tickle ourselves, so that we can be sure when dangerous things, such as bugs, are on us.
Good tickles feel good and can make us laugh. It can be a fun way to play – and humans aren't the only animals that can tickle.
Did you know that when chimpanzees chase and tickle each other they make panting sounds? These pants do not mean that the chimp is tired – they actually mean that it wants to play!
Pets, such as rats, also make noises like laughter when people stroke them.
Laughter and play are good ways for animals (including us!) to make friends . And if you could tickle yourself, you might be less likely to laugh and play with others.
So, there are good reasons why we can only be tickled by others, and not ourselves. But to understand how tickling really works, we'll have to look inside the human body.
The motor system
The motor system is a thing that most animals – including humans – have in their body. It's made up of our muscles and brain, and it's what lets us move
Every time that you move, your brain sends a plan to your muscles. It does this by sending the plan, in the form of electrical signals, along the nerves that run like wires through your body.
This plan tells the muscles when and how to move, and also what to expect when we have moved.
We have five senses: sight, smell, taste, touch and hearing. The plans sent to your muscles guess how each of these senses may change, after you have moved.
So, when you try to tickle yourself, your brain sends the plan through the nerves: it tells the muscles in one arm to move to do the tickling, and it also tells your other muscles that the tickle is coming.
When somebody else tickles you, your muscles haven't got a plan from your brain, so the feeling is surprising – and ticklish!
But you can't tickle yourself, because your brain is always one step ahead, telling your muscles and senses what to expect and stopping you from giving yourself a surprise. But then, maybe it's better that way.