It has always been a mans dream to be able to fly, and many historical events would account for this. Like the invention of the airplanes, spaceships, jets, hot air balloons, and several devices and machines that would literally lift human beings above sky level. Even the myths talk about flight, gods and goddesses capable of gliding through the sky, a prisoners escaping using wings of birds, and the list goes on and on. But never did it happen that we humans were able to fly using our own body.
We always recruit the helps of machinery, science, and engineering in order to create something that would allow us to reach that dream. However, what may seem as an unreachable dream for us turns out to be one that other species of the world attained hundreds of decades ago. If flight is to be talked about, birds would be the first word that comes to mind. Their gracefulness, the way they glide up and down and then suddenly fly out of nowhere just intrigues every scientist from the time of Leonardo da Vinci until today.
They have been used as test organisms in flight simulation studies and modern biology relies on their ancestral lineages to determine evolutionary relationships of this flight mechanisms. However, if one decides to go through an in depth analysis of this mechanism, another group of organisms may be considered. These are the insects a wide, diverse, and varied family of invertebrates that have developed the ability of flying early in their existence. The advantages of using these species are numerous. First they are quite simpler than the birds in terms of structural organization.
Then there is the fact that their diversity contributes to more data in studies. And finally, insects are easily manipulated, easily studied, and easily understood by science. But all this simplicity does not mean that the concepts of the flight of insects are fully elucidated. The whole process itself of an insect creating flight turns out to be very complex, that science is still unable to understand what really is going on. Experiments trying to replicate an insects lifting motion are also considered a great failure.
For science to gain a full understanding of this, it is quite logical to begin from the very start determining the origins of an insects flight. So just how did the mechanism of flight evolved in the family of insects? To be able to move on, one must first understand the principles of a widely accepted theory on evolution, the Natural Selection. This simply states that the evolution of certain organs and body processes results from a selection of a useful trait that would be passed on (Darwin and Ghiselin, 2006).
Therefore, in order for a specific body organ to be passed on to the next generations, it should be of use that would benefit the organism. The speed of a cheetah, for example, benefits the user since it makes him more agile, able to hunt better, and is able to survive threats better than others. This results to the animal having a higher chance of survival, and is able to pass on his speed trait to his offspring. Taking the same concept into the picture, the flight of insects should have evolved because in benefited the host.
And certain studies were able to prove that that just might have been the case. The evolution of insects flight should therefore be seen under the selective pressures that could have improved the utility of the mechanisms (Alexander, 1996). These pressures may range from certain needs, to wants of the organisms for their survival. Also, one must not forget the effects the surroundings and the environment can provide. According to a study by Brodsky, insect flight may be traced back into three different classifications: trivial flight, swarming, and migratory flight (1994).
The obvious cause for this evolution is the need for movement, and this intense movement became the impetus of a very diverse and successful insect radiation. The need for a flying motion can also be attributed to several tactics the insects needed to evolve on early in earth life. One basic necessity is the need to gain food. Having a system that would allow the insects to travel further easier would improve the chances of attaining food and nutrition. Flying can also help the organism in escaping certain threats, such as calamities and enemies.
Others can use flight to gain an edge over competitors, in terms of habitat and female dominance. All of these would allow the insects to have an advantage, and these benefits would allow the flight system to be preferred by evolution. Early flights were also based on the mechanism of a Passive Flight. In here, the insects create a stored energy, and use this as a way of movement from a previous point of flight. Think of it as jumping from a high place. The energy used for initiating the jump is enough, and all the insect needs to do is to maintain its position above the ground.
Examples of this would be gliding and diving, where the insects simply control its position and adjusts to several factors in order to gain maximum displacement. Such parameters would include the air currents, the insects weight and body shape, the size of appendages, and finally, the extension of some sort of glider (Brodsky, 1994). From this point of view, scientists suggested that the precursor of the flying wings were appendages previously used for gliding. They were non-motile, and the insect moves its whole body in order to alter the positions of these gliders.
These were simply used to take advantage of the existing air and wind conditions to achieve a movement much faster and much further than simple walking or jumping (Brodsky, 1994). Using the Passive Flight as a spring board from evolution, one can then relay wing evolution with this. One popular theory on wing evolution relies greatly on the concept of having passive flight as the predecessor of normal flight. This theory, popularized by Muller in 1875, explains the early wings to be simple lobes on the sides of an insects body. These are immobile, and functions mainly to stabilize the insect in times of landing.
Since all flight at that time were supposed to be passive, the insects needed a way to drop out of flight and land properly, not harming themselves (Alexander, 1994). Especially in food gathering in high vegetations, controlling the big drop to ground is a big need for insects. Natural selection then naturally chooses this trait since it benefits the hosts. And since it also provides protection and improves survival rate, the insects with these feature are able to live longer and can pass these lobes onto the next generation. The fast breeding time of insects could have resulted to a quicker evolution on these lobes.
Eventually, after thousands of generations, evolution extended these lobes even more, and later on motor, sensory, on neuron cells grew on the forming, making it capable of flapping and thus, of flying on its own (Hinton, 1963). Another theory that looks the other way depends on the other side of the mechanism of flight. As the first theory suggests that wings started as inactive lobes, this theory, called the Leg-excite theory, states otherwise. The proponent of this explanation was originally by a man named Oken in 1811, and then later on resurfaced by Wigglesworth (Wigglesworth, 1963).
Much of its success must also be attributer to Jarmila Kukalova-Peck, who provided numerous physical evidences needed. They suggested, and proved, that the early wings were in fact mobile elements, capable of flapping even before the actual flight evolved. The strong evidence of this lies on the homology of wings with that of an external gill found in the insect Ephemeroptera, which is mobile and has all systems required for motility, such as the motor, sensory, and neuron cells mentioned previously (Kukalova-Peck, 1991).
These two main theories still further branch out into other explanations to improve the primary evidences shown. For example, in the passive flight point of view, some suggested that the insects that first evolved into this system were fast runners and leapers, and used their lobes as a balance in order to quickly evade predators. This is logically correct, although evidences show that insects are capable of jumping to a distance not high enough for gliding to occur. Nor are they fast runners to attain such speed needed for the flight (Ellington, 1984).
This is however weak since as of todays technology, there is no physical way to determine the capabilities of insects during prehistoric times. All of these conclusions were just made from speculations and evidences from archeological studies. Proponents of this theory also suggested another variation, on which that the gliding effects were first portrayed by insects with large gills, and that the reachable speeds of these insects were enough to glide across water (Marden and Kramer, 1994). They are relatively small insects, and the needed speed in order to do a horizontal glide was possible.
Also, the lack of jumping or leaping in this process strengthens the postulates by removing the need for a high jumper in order to attain flight. This was proven using stone dragonflies as subjects, were this specific gliding procedure using the wings was observed. Today, the evolution of insects flight is still a heated debate over scientists, which is not surprising as of the moment. To be able to correlate with the answers, scientists should be able to tackle three dimensions of the problem. First is how the wings started.
Are they already there from the beginning? Are they useful immediately from birth? Next they must be able to explain how the actual flight began. Did it evolved from gliding? Or were the wings already capable of flapping and flying? And finally, there lies the question on the aerodynamics of the past and current environment. How did the wind and air patterns contribute to the evolution of wings and flight? Though some of these have been already answered, the problem lies in synchronizing the answers to come up with a single solution.
Some answers, like the evidences of a moving gill in Ephemeroptera, would support the existence of an already present wing. This however, leads to more questions on what would be its primary purpose and what led it to evolve into the modern wing we now already know about? It is still a long and tedious process, but progressions in science would eventually lead to the satisfying answers, and maybe we humans can put into good use the knowledge we would attain from this.
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Hinton, H. E. (1963). The origin of flight in insects. Proc. R. Ent. Soc. Lond. C, 28: 24-25. Kukalova-Peck, J. (1991). Fossil history and the evolution of hexapod structures. In The Insects of Australia, 2nd Ed. , Vol. 1 (ed. by I. D. Naumann), Cornell Univ. Press, Ithaca, pp. 141-179. Marden, J. H. , and Kramer, M. G. (1994) Surface-skimming stoneflies: A possible intermediate stage in insect flight evolution. Science 266: 427-430. Wigglesworth, V. B. (1963) The origin of flight in insects. Proc. R. Ent. Soc. Lond. C, 28: 23-24.