On Balance

"In the temporal bone are housed two organs with the function of hearing and equilibrium. Seemingly unrelated, one's curiosity asks why nature has seen fit to have them so associated.
The answer is that the two functions are basically the same. The posterior-superior division of the labyrinth retains its original role of motion sensing, the anterior inferior portion manifesting a highly specialised form of the same function. The two parts, vestibular and cochlear, communicate freely and are simultaneously affected by body movement and by external molecular movement called sound waves. Always the ear is a motion sensing apparatus."

Guggenheim, L. (1948) 'The Phylogenesis of the Ear' , Culver City, CA, Murray & Gee Inc.

Sometimes it takes a completely utilitarian look at something to surprise you. This book traces the evolutionary developments of the ear, right from the balancing apparatus of protozoa through to modern man, and it's full of little gems like this first paragraph in the introduction. I love the fact that our hearing ears developed out of organs that were there to keep our distant ancestors the right way up, and linking sound and equilibrium through this device makes a nice change to the acoustic spacial perception/computation thing we often hear about.