Classic evolution as one feature is progressively improved to perfection.
The golden tree frog of Malaysia is a treetop acrobat. Usually it hops just a few metres, but if it meets a golden tree snake it makes a leap into the unknown to make its escape. As it plummets, it spreads its limbs to slow its descent and its webbed feet double up as a parachute. The Javan flying frog goes one better. Its webbed feet have developed into miniature wings, so instead of parachuting it paraglides at an angle. But the Wallace frog has huge webbed feet which become aerofoils creating a slow, controlled descent - it can glide as far forwards as the distance it falls. Lizards lack webbed feet, so they have expanded other body features to get their wings. The flying gecko's impressive glide angle is due to wing-like fringes on its body, where every available edge becomes an aerodynamic extension. But the draco lizard has developed a huge aerofoil, turning the lizard into a flying frisbee. The large flap of skin is supported by foldable ribs and its tail steers like a rudder. The golden tree snake use other tricks for its leap of faith: it loops its body for the ultimate take-off and projects forward to gain a head start. It then flattens into a ribbon and swims through the air using the 'S' shape of it's body.