On multiple occasions I have heard the bacterial flagellum (pictured above) used as evidence of irreducible complexity in biology, an argument often used by promoters of intelligent design. After examining this diagram it is not difficult to imagine why promoters of ID would claim it as evidence. The bacterial flagellum is a complex and rigidly organized appendage that superficially appears to be an intricately planned machine rather than an accidental biological structure. And if such an intricate thing looks too complex to be reduced or to have evolved from simpler forms, what other explanation remains except design? However, as with most arguments for intelligent design, evoking irreducible complexity is a fallacious action based on naive conceptions of biology and evolution.
Bacterial organisms have existed on Earth for the past 4 billion years, a very long time for evolutionary processes to be taking place, and have adapted to live in virtually every conceivable environment. Populations of bacteria grow exponentially, with billions of generations produced in a relatively brief period of time, allowing natural selection to have a very strong influence. Evolutionary biologists have theorized that large populations of organisms are more readily influenced by natural selection and that prokaryotes, bacteria and archaea, more readily exchange genes amongst each other. Therefore a large population of prokaryotes evolving over a vast period of time would predictably possess very intricate and complex biological structures. The bacterial flagellum is no surprise or dilemma for evolutionary biologists, in fact it is expected.
Utilization of the bacterial flagellum, or any other so-called irreducibly complex biological structure, as evidence of design is itself an evidence, evidence of a clear misunderstanding of biology and ignorance of evolutionary processes. Anyone who would challenge the modern theory of evolution with intelligent design either does not understand the widely accepted, peer reviewed science they are challenging or has been blinded by their religious convictions. After all ID is a religious view, not a scientific theory, supported almost exclusively by Christians, not scientists. Irreducible complexity is just one in a long line of fallacies promoted by the ID camp that poses no serious challenge to legitimate science.
Intelligent design and its supposed evidences are intellectually dangerous because they provide the public a falsified view of biology and evolution and the religious an erroneous vindication in denying the prevailing views of science. None of the discoveries in the fields of evolutionary biology, genetics, paleontology, etc have done anything except substantiate the accidental, impersonal, material processes of evolution as the best explanation for the origin and development of life. Irreducible complexity is a product of scientific illiteracy and religious conviction, not good science, and denying the true origins of astounding, beautifully complex biological structures like the bacterial flagellum only diminishes those astounding and beautiful qualities.