What is Irreducible Complexity?

Answer

Irreducible complexity is a term used to describe a characteristic of certain complex systems whereby they require all of their individual component parts in place to function. In other words, it is impossible to reduce the complexity of an irreducibly complex system by removing any of its component parts and still maintain its functionality.

Professor Michael Behe of Lehigh University coined the term in his seminal work “Darwin’s Black Box” in 1996. He popularized the concept by using the common mousetrap as an example of irreducible complexity. A typical mousetrap consists of five integral parts: a catch, a spring, a hammer, a holding bar, and a foundation. According to Behe, if any of these parts are removed without a comparable replacement (or at least a significant restructuring of the remaining parts), the entire system will fail to function. Professor John McDonald of the University of Delaware has challenged the irreducible complexity of the mousetrap. McDonald has created an online flash presentation to illustrate his argument (see “A reducibly complex mousetrap” at http://udel.edu/~mcdonald/oldmousetrap.html). Behe has published a rebuttal to McDonald’s argument, also online (see “A Mousetrap Defended: Response to Critics” at http://www.arn.org/docs/behe/mb_mousetrapdefended.htm). And so the debate over the mousetrap continues. However, whether or not the mousetrap is truly irreducibly complex is not the crux of the matter. The essence of the issue lies in the concept of irreducible complexity itself.

The seemingly innocuous concept of irreducible complexity sparks intense controversy when applied to biological systems. This is because it is viewed as a challenge to Darwinian evolution, which, undoubtedly, remains the prevailing paradigm in the field of biology. Charles Darwin acknowledged, “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” (Origin of Species, 1859, p. 158). Behe argues, “An irreducibly complex system cannot be produced directly (that is, by continuously improving the initial function, which continues to work by the same mechanism) by slight, successive modifications of a precursor system, because any precursor to an irreducibly complex system that is missing a part is by definition nonfunctional” (Darwin’s Black Box, 1996, p. 39).

It should be noted that by “nonfunctional” Behe does not mean that the precursor cannot serve any function – a mousetrap missing its spring can still act as a paperweight. It just cannot serve the specific function (catching mice) by means of the same mechanism (a spring-loaded hammer slamming down upon the mouse).

This leaves open the possibility that irreducibly complex systems can evolve from simpler precursors which serve other unrelated functions. This would constitute indirect evolution. Behe has conceded that “if a system is irreducibly complex (and thus cannot have been produced directly), however, one can not definitely rule out the possibility of an indirect, circuitous route” (ibid, p. 40).

In keeping with the mousetrap analogy, while a five-piece spring-loaded mousetrap couldn’t evolve directly from a simpler, nonfunctional version of itself (and remain in line with Darwin’s concept of evolution by means of natural selection), it might evolve from a four-piece paperweight. Thus, according to Behe, a more effective, more complex mousetrap evolving from a simpler version of itself would constitute direct evolution. A complex mousetrap evolving from a complex paperweight would constitute indirect evolution. Irreducible complexity is seen as a challenge to direct evolution.

It should also be noted that evolution by means of natural selection does not solely act to complicate precursory systems. It can also simplify them. Thus, Darwinian evolution

One can create irreducible complexity by working in reverse. Take the well-known game Jenga, where players pull out wooden blocks from a tower until it falls. The tower starts with 54 wooden blocks. As blocks are removed, the tower becomes less complex (meaning, there are fewer and fewer parts) until it reaches irreducible complexity (meaning, if more blocks are removed, the tower will collapse). This demonstrates how an irreducibly complex system could develop indirectly from a more complex system.

Behe suggests that the simpler an irreducibly complex system is, the more likely it could have evolved indirectly (either by evolving from a simpler precursor with a different function or from a more complex precursor that lost parts). On the contrary, the more complex an irreducibly complex system is, the less likely it could have evolved indirectly. Behe states, “As the complexity of an interacting system increases, the chance of such an indirect route decreases significantly” (ibid, p. 40).

Behe uses the example of the E. coli bacterium’s flagellar system as a complex irreducibly complex system that he believes could not have evolved directly (due to its irreducible complexity) and probably did not evolve indirectly (due to its extreme complexity). The E. coli flagellar system is an amazing microscopic outboard motor that E. coli use to move in their environment. It consists of 40 individual, essential parts including a stator, a rotor, a driveshaft, a u-joint, and a propeller. If any of these parts are removed, the entire system will cease to work. Some of the flagellum’s parts are found elsewhere in the microscopic realm. These parts also serve as components of the Type III transport system. Therefore, they may have been borrowed from a Type III transport system (a process called cooption). However, most of the E. coli flagellar components are unique. They need th

Each biological system has its own evolutionary explanation, which, as of now, remains enigmatic.

There has been significant opposition to irreducible complexity from within the Darwinist community. Some of this criticism is valid, while some is not. It is essential to carefully examine the assertions made by advocates of irreducible complexity. Some of the biological instances initially cited by proponents now seem to be reducible. However, this does not invalidate the concept itself, nor does it dismiss actual instances of irreducibly complex biological systems (such as the E. coli bacterial flagellum). It simply demonstrates that scientists, like everyone else, can make errors.

In essence, irreducible complexity is a component of the Intelligent Design Theory that posits certain biological systems are incredibly intricate and reliant on multiple complex components, making it implausible for them to have evolved by chance. If all parts of a system did not evolve simultaneously, the system would be nonfunctional, thus becoming a hindrance to the organism. Consequently, based on the “laws” of evolution, it would be naturally eliminated from the organism. While irreducible complexity does not explicitly validate an intelligent Designer, nor definitively disprove evolution, it undeniably indicates something beyond random processes in the origin and progression of biological life.