The flagellum is a curious organism that has fascinated and amazed scientists over the course of 200 years. The winner-take-all publicity of Charles Darwin is one that has set the current bar of how "popular science" embrace the tiny organelle of movement; found attached in the cells of organisms. There are 3 types of flagellum:
1. Bacterial flagella - helical filaments that move like screws. They provide two of several kinds of bacterial motility.
2. Archaeal flagella - superficially similar to bacterial flagella. non-homologous.
3. Eukaryotic flagella - animal, plant, and protist cells: complex cellular projections that lash back and forth. It's microscopic detail is essential to survival for water-dwelling cellular organisms, creating currents of respiration and circulation for sponges and invertebrates. The word flagellum comes from Latin, meaning "whip".
According to some anti-evolutionists, the eubacterial flagellum is a major point of discussion. Anti-Darwinians have amassed a spectrum of sound and solid evidence from healthy skepticism, spawning a long-awaited movement coined "Intelligent Design". The existence of the flagellum counters "precursor systems" in that it poses an a-typical structure that cannot be claimed to have come from minor shifts in time. "Intelligent Design", simply put, classifies some organisms as irreducibly complex. Meaning, the design of the organism could not have come from evolution but rather designed from an outlier: intelligent design unit that operates outside the laws of nature. Simply put, Natural Selection can only choose what already exists, leaving the question for the flagellum hanging in the wind; the flagellum, along with living cells, are filled with complex structures that lack any detailed evolutionary origins. This is based on a form of empiricism known as "skeptical empiricism", which cancels out Darwin's personal statement: if one could find an organ or structure that could not have been formed by "numerous, successive, slight modifications," [his] "theory would absolutely break down" (Darwin, The Origin of Species 1959 pg. 191.