From Scientific American:
Go into any busy coffee shop and you are likely to see people engrossed in conversation, waving their hands around. A man at the counter describes the coffee he wants to buy – in a mug, not a to-go cup – and his hand takes a familiar shape, as if he were already holding the cozy mug. Nearby, two sisters laugh, as one tells a story about a trip to the barrier reef and all of the fish that she saw, her hands wiggling and darting in an invisible sea in front of her. The drive to gesture when speaking is fundamental to human nature.
If you have thought about why we gesture you probably assumed that we gesture to help others understand what we are saying. Pretending to hold a ceramic mug can help the barista understand exactly which mug you want. Showing how the fish darted to and fro can help your sister get a more vivid picture of what the reef looked like to you. But might gesture also serve another purpose? Many scientists now think that gestures can help the person making them — that moving your hands can help you think. Researchers have become increasingly interested in the connection between the body and thought – in the ways that our physical body shapes abstract mental processes. Gesture is at the center of this discussion. Now the debate is moving into learning, with new research on how students learn to solve math problems in the classroom.