In experiments where the active use of gesture is inhibited, subjects show decreased performance on various kinds of mental tasks.

It is noteworthy, for example, that the use of spontaneous gesture increases when we are actively thinking a problem through, rather than simply rehearsing a known solution. There may be more to so-called “handwaving” than meets the eye.

Uniting these fields is the thought that evolution and learning don’t give a jot what resources are used to solve a problem. There is no more reason, from the perspective of evolution or learning, to favor the use of a brain-only cognitive strategy than there is to favor the use of canny (but messy, complex, hard-to-understand) combinations of brain, body and world.