The nature of flight

Abstract

Since the dawn of civilization, humans have envied their feathery companions for their ability to leap from the earth, escape gravity—and all earthly problems—and ascend to the skies. Of course, humans eventually made it into the skies too, albeit after a few millennia and rather inelegantly with the help of technology. Even so, we can now fly around the Earth in a matter of hours or zoom about in a fighter plane at supersonic speeds. Yet, flying has never lost its fascination for humans, and many scientists continue to study how various species have mastered the physical and metabolic challenges of flight. Many of the basic questions regarding aerodynamics and the physical mechanics of flight—including the fundamental one of how the bumblebee manages to stay in the air—have largely been resolved. Now, the spotlight has moved to focus on the underlying metabolic and molecular mechanisms that enable animals to fly. ![][1] The ability to fly appears to have evolved separately at least four times: in birds, bats, insects and pterosaurs. Although pterosaurs are extinct, the other three provide unique opportunities to study the aerodynamic and molecular features of animal flight. The evolution of flight in both vertebrates and invertebrates has led to a wide variety of adaptations to exploit unique physiological advantages and to overcome specific deficiencies. For example, size matters and, owing to various mathematical laws, smaller animals have to flap their wings faster to stay in the air. Furthermore, air resistance is a more significant problem for smaller animals, which means that there is an effective minimum size for flight. Yet other factors mean that flying animals also cannot be too large; oxygen and sugars have to travel further around the body, and the power required for take off is proportionately greater—as can be seen by watching how large … [1]: /embed/graphic-1.gif