The Wings in Animals
Again, natural conditions seem to have been the initiator of the development of the wings on all flying animals, which at their earliest stage—at a time when no living creatures were able to fly—could have been very simple in form. It is possible that the wings might have taken such a form as shown in the illustration below.
The multicellular body is round, light, and feathery, which enables it to drift, blown away with ease even at the slightest movement of the wind. The black circle inside the multicellular body represents the centre of gravity, such that even during flight it will always stay in the position as shown in the illustration.
To help ease understanding, a two-dimensional illustration of the wing is given below. What is actually happening when the creature is in the air? Obviously, each time the creature dives or drifts, the wind from beneath the body flows upwards. The illustration shows the flow of the wind from a to m and n. In the meantime, on the upper part of the body, the wind at b spins. The flow of the winds that is closest to the body collides with the whirl at b, which as a result causes the winds (m and n) to flow in the direction of b and together they then follow the whirl. This result in the feathers located at the black triangle being pulled towards that position as indicated by the straight arrow. Although the pull of the wind may not be quite strong, the continuity with which it occurs, from generation to generation, is such that even a change as minute as one Angstrom passed on to the next generation can make the feathers grow longer.
As has been said earlier, the flying-creature-to-be is just one phase of the form undergoing evolution, wherein such characteristic as the ability to control the body is developed. In this case, it is the lengthening of the feathers. Thus, when drifting in the wind, it has by then already had the ability to steer its flight in any direction it wishes to go.
Millions of years later, it begins to gain greater control of its body as its long feathers have by then turned into wings. The flying creature has by then already had not only the ability to determine itself where it wishes to go but also the ability to lift itself up into the air without the help of the wind.