Stability vs. Agility in Animal Flight

I just read an article by John Maynard Smith called "The Importance of the Nervous System in the Evolution of Animal Flight". Smith's message was simple but helped me understand some principles of animal flight that I have overlooked before.

Stability in flight can be described as how well an aircraft resists rotation in the horizontal or vertical axes as it is acted upon by external forces. Stability is opposed to maneuverability. To make an aircraft more maneuverable it has to be fundamentally less stable. A less stable, more maneuverable aircraft requires a more skilled pilot to fly it successfully. This translates to the need of an enhanced nervous system and acute muscle control in less-stable flying animals.

There are two classes of airborne animals: gliders and true fliers (the difference being in non-powered versus powered flight). Gliding is thought to be a more primitive form of flight and, indeed, of the four lineages of powered fliers evidence suggests that flight progressed from gliders to stable fliers to unstable fliers. The pinnacle of powered flight is something like the common house fly. This fly is so agile in flight that it requires precise and rapid sensory perception and motor reflex so it can instantly change trajectory in any direction. This feat requires a well developed nervous network. In the robber fly who hunts other winged insects, we also see the ability to predict the trajectories of prey and intercept them in-flight. These predators know no limits: if it's an insect with wings, they can bring it down.

Photograph by Fir0002/Flagstaffotos. Used with permission under GFDL: http://en.wikipedia.org/wiki/GNU_Free_Documentation_License