Irreducibly complexity (IC) is a conceptual test for intelligently designed components or system. It is asserted that if a system cannot be reduced to fewer components and retain functionality, then it could not have evolved by the gradual assemblage of components over successive generations.
The concept was popularized by Lehigh University biochemist Michael Behe in his 1996 book Darwin's Black Box. Intelligent design theorists argue that while some systems and organs can be explained by evolution, those that are irreducibly complex must have been assembled by an agent of intelligence.
There are many examples of molecular machines, such as the bacterial flagellum, that are composed of numerous elements. Behe rightly points out that such machines are irreducibly complex in that if any one part were removed, the function in question would be instantly lost. How then could such a machine be built up gradually if it will not work to any selectable degree until all its parts are present in their proper order?
Darwin knew his theory of gradual evolution by natural selection carried a heavy burden:
|“||If it could be demonstrated that any complex organ existed which could not possibly have been formed by numerous, successive, slight modifications, my theory would absolutely break down. But I can find out no such case.||”|
The term "irreducible complexity" was originally defined by Behe as:
|“||a single system which is composed of several interacting parts that contribute to the basic function, and where the removal of any one of the parts causes the system to effectively cease functioning. An irreducibly complex system cannot be produced gradually by slight, successive modifications of a precursor system, since any precursor to an irreducibly complex system is by definition nonfunctional. Since natural selection requires a function to select, an irreducibly complex biological system, if there is such a thing, would have to arise as an integrated unit for natural selection to have anything to act on. It is almost universally conceded that such a sudden event would be irreconcilable with the gradualism Darwin envisioned. At this point, however, 'irreducibly complex' is just a term, whose power resides mostly in its definition. We must now ask if any real thing is in fact irreducibly complex, and, if so, then are any irreducibly complex things also biological systems.||”|
William Dembski, another advocate of intelligent design, gives this definition:
|“||A system that performs a primary function is irreducibly complex if it includes a set of individual parts in a non arbitrary well-arranged way, which interact, so that each part is in all essential to maintain the basic function, and therefore original of the system. The set of these parts is known as the essential irreducible core system.||”|
Irreducible complexity vs. Cumulative Complexity
According to Dembski, the irreducible complexity should be contrasted with cumulative complexity. A system is cumulatively complex if the system components may be arranged sequentially such that a successive removal of components not lead to a complete loss of function.
- Darwin, Charles (1872) Origin of Species 6th ed (1988), p.154, New York University Press, New York.
- Molecular Machines: Experimental Support for the Design Inference by Michael Behe
- Behe, Michael J (1996). Darwin´s Black Box:The Biochemical Challenge to Evolution. New York: Touchstone/Simon & Schuster. p. 39-40. ISBN 0-684-83493-6.
- Dembski, William (2007). No Free Lunch:Why Specified Complexity Cannot Be Purchased without Intelligence. Rowman & Littlefield Publishers. p. 285. ISBN 0-74255810-X.
- Dembski, William A (1999). Intelligent Design:The Bridge Between Science & Theology. Downers Grove, Illinois: IVP Academic. ISBN 0-8308-2314-X.
- Evidence for Intelligent Design from Biochemistry by Dr. Michael Behe
- Irreducible Complexity Revisited by William Dembski. PCID Volume 3.1, November 2004
- Argument: ‘Irreducible complexity’ by Jonathan Sarfati
- Evolving the Irreducible: Behe's Mousetrap Problem by Sean D. Pitman M.D.
- Behe's Reply to his Critics