Roland Piquepaille writes "Physicists from Duke University have applied the so-called 'constructal theory' to explain how running, flying and swimming modes of locomotion are similar even if they're apparently unrelated. This single unifying physics theory explains how fast animals get from one place to another and how rapidly and forcefully they step, flap or paddle in relation to their mass. In other words, these scientists argue that the characteristics of animal shape and locomotion are predictable from physics." For more details see the Duke Press release or Roland's blog. You can read more about constructal theory at the Constructal Theory Web Portal. Understanding animal locomotion could have interesting implications for the design of walking robots.