Rolling Animals

Rolling Animals

Rotating locomotion encompasses two distinct modes of locomotion: simple rolling, and spinning relative to a fixed axle or body in the manner of a wheel or propeller. Several organisms move by rolling. However, despite the integral role that the wheel has played in locomotion of vehicles designed by humans, true wheels do not appear to play any role in the locomotion of biological systems. The reasons for this apparent lack of biological wheels have been expounded on by biologists, and wheeled creatures have appeared in numerous works of speculative fiction.

Given the apparent utility of the wheel in human technology, and the existence of biological analogues of many other human technologies (such as wings and lenses), it might seem odd that a true wheel has never evolved naturally, but this lack of biological wheels is typically explained by two main factors: first, there are several developmental and evolutionary obstacles to the evolution of a wheel by natural selection, and secondly, wheels often do not carry a competitive advantage over other means of propulsion (such as walking, running, or slithering) in the environments in which ambulatory species have evolved. (This lack of an advantage in certain environments incidentally explains why some human civilizations have eschewed wheels, despite their awareness of the technology.)

This article begins by examining known naturally occurring examples of rolling and wheel-like motion. Next, the constraints on wheeled motion imposed by evolution and by the nature of biological development are discussed, addressing the question, "Why can't a true wheel evolve?" This is followed by a summary of the disadvantages of wheels when compared with limbed locomotion, addressing the question, "If wheels could evolve, why would they be unlikely to do so?" Finally, examples of rotating locomotion in fiction and legend are presented.