Why are we ticklish?

I know that chimps are definitely ticklish (having been a zookeeper after college), but as to why? No idea. But I want to find out.

For calling attention to scorpions crawling on unseen parts of our bodies.

And yes, animals are ticklish. Try tickling the toe-pads of a dog or cat, but be ready to yank your hand back before it gets chomped or scratched!

My dog is ticklish. And I think I might be the most ticklish creature in the world.

We usually feel extremely small.