Irreducible complexity is a bogus argument that creationists use to counter evolution. They claim that some features in animals could not have evolved gradually, but must have evolved all at once, in full complexity. For example, creationists tried to claim the eye was irreducibly complex. They argued a partial eye was useless. Yet you can find living creatures with every stage of eye evolution who find the intermediate stages useful. Half sight is better than no sight. More recently, creationist Hans Behe claimed the flagellum was irreducibly complex. He ignored that various intermediate stages had uses other than a flagellum. Evolution cannot plan ahead. Evolution borrows from whatever structures exist already rather than evolving new ones.
There are no known legitimate examples of irreducible complexity. These are a fiction of the creationists. If you think you have found one, google it to find out why it not irreducible.~ Roedy (1948-02-04 age:70)