The power of the wind to propel insects along the surface of water by blowing against an upraised appendage may have played a vital role in the evolution of flight in insects. The theory of evolution proposes that organisms can change gradually because of natural selection over long periods of time.
Creationists reject evolution and claim that the species of life we now know were each created separately in their present forms, and that species have no inherent capacity to change into new species.
The creationists use many arguments in an attempt to demonstrate the absurdity of the theory of evolution. A commonly used argument is to point to a complex biological organ, e.g. the eye, which has several parts, each of which must perform its own particular function perfectly if the whole organ is to perform its overall function.
Remove, or seriously impair, one of the component parts and the entire mechanism fails.
The creationists ask how such a mechanism could slowly evolve from successively less complex mechanisms. Would not an eye in an early stage of its evolution, half blind and producing a grossly distorted image of the world, be a hindrance, not an advantage, contributing to the demise rather than the well-being of its owner, they ask.
This is a valid question and is taken very seriously by evolutionists. Darwin himself took pains to deal with this question.
In recent years, Richard Dawkins has written several books on evolution for the general reader. Dawkins is very good at explaining how complex organs such as an eye can slowly evolve in small steps over many generations.
I recommend two of his books in particular to the reader who wishes to pursue this matter in some detail: The Blind Watchmaker and River Out of Eden.
The development of the capacity to fly was a major evolutionary milestone in the insect world. We can easily understand this when we consider how, in our own species, the ability to take to the air, discovered only 94 years ago, has transformed human culture.
Hundreds of millions of years before humans arose, the ability to fly precipitated an explosive increase in the rate of evolution of insect species. Two thirds of all species on earth today are flying insects.
The difficulty of visualising how the ability to fly could gradually evolve was recognised soon after Darwin and Wallace proposed the theory of evolution.
Flight depends on wings, wing articulations, nerve circuits and powerful flight muscles. How could this complex mechanism develop in small increments?
After all, would not a partly evolved, faulty flying-machine do its owner more harm than good? One of Darwin's critics asked: "What good is a nub of a wing?"
And if no good, what advantage could it confer that would allow it to be preferred by natural selection?
To date, the fossil record has been of no help in working out the various stages in the evolution of insect wings. Insect wings first appear in the fossil record fully formed.
Apparently, earlier climatic conditions prevented fossilisation - there is a great scarcity of wingless insects in the old rocks. Ecologists therefore can only speculate as to how wings evolved.
James Marden, a biologist at Pennsylvania State University, has proposed a credible mechanism.
It had earlier been proposed that insect wings may have evolved from the movable articulated gill plates of ancient aquatic insects. These insects used their gill plates not only to breathe underwater but also, by beating the plates, to propel themselves forward.
But why would it be advantageous for the early aquatic insects to move onto the water surface, and later to move entirely up into the air?
It was a great advantage for the aquatic insects to move onto the water surface because, in so doing, they moved into predator-free space. The fossil record suggests that until relatively recently most fish fed along the bottom or within the water column.
Surface-feeding fish, which can take insects from the water surface and from the air, arose only relatively recently.
Therefore, by rising onto the water surface, aquatic insects escaped their enemies and began a turbo-charged phase of development. Air is 50 times less viscous than water, allowing insects to move faster, freed of the exhausting effects of drag and the necessity to keep their bodies streamlined.
On the water surface, body shapes and functions could develop that would be a deadly encumbrance beneath the surface. Rates of procreation were speeded up and full rein was given to the creativity of insect genes.
A liquid displays a property called surface tension where its surface interfaces with the air. Surface tension is a sort of invisible skin on the surface of the liquid.
Water has quite a high surface tension and, to a small insect, the water surface presents itself as a flexible, slippery but solid surface along which it can slide, just as a skater can slide on ice.
Anyone who has skated on open ice knows that you can "sail" simply by opening your anorak and holding it wide with outstretched arms. The wind will catch the coat and blow you along.
Marden suggests that this was how flight began to develop in insects. He has observed that modern water insects (stoneflies) harness the power of the wind to sail along the surface of water simply by raising their stubby little wings.
Because they perform a function besides flying, the movable aerodynamic wings of flying insects provide evidence that wings may pre-date flight.
When the ancient aquatic insects moved to the water surface, raising movable gill plates into the air would have given them the ability to skim the surface. The water surface would have given natural selection an opportunity to act on these "nubs of wings" and to develop and refine them for later flight.
However, it must be admitted that this matter can be finally settled only when someone brings forward direct fossil evidence of the first winged insects.
William Reville is a Senior Lecturer in Biochemistry at University College Cork