Irreducible complexity
In biology, irreducible complexity is an unorthodox concept developed by Lehigh University biochemist Michael Behe in his 1996 book Darwin's Black Box. The concept supports the intelligent design theory, and challenges mainstream scientific beliefs on evolution.
Michael Behe defined irreducible complexity in Molecular Machines: Experimental Support for the Design Inference as follows:
What is irreducible complexity?
For example, a wall is not irreducibly complex: if one were to remove a brick, or a number of bricks, the wall would still stand up and perform its function - to provide some (reduced) level of shelter. On the other hand, a standard mousetrap is irreducibly complex. It contains five independent parts: hammer, spring, catch, holding bar, and platform. If one of these parts is missing, then the mousetrap cannot catch any mice.
The debate on irreducible complexity concerns two questions:
- Can irreducible complexity be found in nature?
- What would the significance be if it were?
Forerunners
The argument from irreducible complexity is a descendant of the teleological argument for God (the argument from design or argument from complexity). This states that because certain things in nature are very complicated, they must have been designed, just as the existence of a watch implies the existence of a watchmaker. This argument is a very old one, and can be traced back as far as Cicero's De natura deorum, ii. 34 (see Hallam, Literature of Europe, ii. 385, note).
Charles Darwin's theory of evolution challenges the teleological argument by postulating an alternative explanation to that of an intelligent designer: namely evolution. The argument from irreducible complexity attempts to demonstrate that certain biological features cannot be purely the product of evolution.
Behe argues that organs and biological features which are irreducibly complex cannot be wholly explained by current models of evolution. He argues that:
Alternatively, it may be that irreducible complexity does not exist in nature: that the examples given by Behe and others are not in fact irreducibly complex, but can be explained in terms of simpler precursors.
The precursors of complex systems, when they are not useful in themselves, may be useful to perform other, unrelated functions. To stretch the example of the mousetrap, a "broken" proto-mousetrap might not catch mice but the components might serve other useful and completely unrelated purposes (paperclip, power supply to a toy car, hinge, etc). Evolutionary biologists say that evolution often works in this kind of blind, haphazard manner in which the function of an early form is not necessarily the same as the function of the later form. The mammalian ear (derived from a jawbone) and the panda's thumb (derived from a wrist bone spur) are classic examples of this.
Evolution can act to simplify as well as to complicate. This raises the possibility that apparently irreducibly complex biological features may have been achieved with a period of increasing complexity, followed by a period of simplification. Consider the example of the wall, which is not irreducibly complex. If you remove bricks at random from the wall, one at a time, eventually you end up with something that will fall down if you remove one more brick. Such a structure could not have been created only by adding bricks one at a time.
Behe has been accused of using an argument by lack of imagination, or constructing a "God of the gaps". Behe acknowledges that simply because scientists cannot currently see how an "irreducibly complex" organism could evolve, it does not prove that there is no possible way for it to have occurred.
Some critics, such as Jerry Coyne (professor of evolutionary biology at the University of Chicago) and Eugenie Scott (pro-evolution activist, Executive Director at the National Center for Science Education) have argued that the concept of irreducible complexity, and more generally, the theory of Intelligent Design is not falsifiable, and therefore, not scientific.
Behe argues that the theory that irreducibly complex systems could not have been evolved can be falsified by an experiment where such systems were evolved. For example, he posits taking bacteria with no flagella and imposing a selective pressure for mobility. If, after a few thousand generations, the bacteria evolved the bacterial flagellum, then Behe believes that this would refute his theory.
Other critics validate this defence, by pointing to experimental evidence that they believe falsifies the argument for Intelligent Design from irreducible complexity. For example, Kenneth Miller cites the lab work of Barry Hall on E. coli, which he presents as conclusive evidence that "Behe is wrong".
Behe and others have suggested a number of biological features that they believe may be irreducibly complex.
The flagella of certain bacteria constitute a molecular motor requiring the interaction of about 40 complex protein parts, and the absence of any one of these proteins would make the flagella fail to function. Behe holds that the flagellum "engine" is irreducibly complex because if we try to reduce its complexity by positing an earlier and simpler stage of its evolutionary development, we get an organism which functions improperly. According to the principle of natural selection, it would die out soon.
One mechanism which refutes this argument is "scaffolding", where a set of biochemical reactions are used to build up a pathway and then are discarded, in much the same way that a building is built from the bottom up even though removing any of the columns would cause the building to collapse.
Proponents of irreducible complexity argue that without all the components present, the beetle would blow itself up or the remaining parts would serve no useful benefit.
Conclusions from irreducible complexity
Irreducible complexity is not an argument that evolution does not occur, but rather an argument that it is incomplete. If irreducible complexity cannot be wholly explained by current models of evolution, then alternative models must be considered such as:Opposition to irreducible complexity
Falsifiability and experimental evidence
Examples
Flagella
Main article: Evolution of flagellaLight detection
The biochemistry of light detection requires complex interactions among many different molecules, each performing a very specialized job. Eliminating even one component of the biological pathway can destroy the ability to detect light.The bombardier beetle
The bombardier beetle (Genus Brachinus) is an organism that has become somewhat of a standard bearer for irreducible complexity. These beetles have three chambers in their abdomen, two of which contain liquids that are chemically inert, but when mixed they create an incendiary combination. The third chamber is a reaction chamber into which the two chemicals are squeezed when danger is near, and then expelled explosively towards the perceived danger.Other examples
External links and further reading
