Irreducible complexity is a controversial concept popularized by Lehigh University biochemist and Fellow of the Discovery Institute Michael Behe in his 1996 book Darwin's Black Box. Behe contests some aspects of the generally accepted scientific theory that life evolved through biological evolution by natural selection alone and asserts that some additional mechanism is required, arguing that there are biochemical systems that are irreducibly complex because he sees no way to break them down into functioning pre-systems. Accordingly, his book supports what is known as intelligent design, a form of the argument from design, one of many arguments for the existence of a supernatural deity.
Irreducible complexity is not recognised by the majority of scientists, who argue that Behe uses an argument from ignorance, that Behe fails to provide a testable hypothesis, that there is a lack of evidence supporting the concept and therefore creationist pseudoscience.
Definition
The term "irreducible complexity" is 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". (Michael Behe, Molecular Machines: Experimental Support for the Design Inference)
Supporters of the intelligent design theory use this term to refer to biological systems and organs that could not have come about by an incremental series of small changes. They argue that anything less than the complete form of such a system or organ would not work at all, or would in fact be a detriment to the organism, and would therefore never survive the process of natural selection. Although they accept that some complex systems and organs can be explained by evolution, they claim that organs and biological features which are irreducibly complex cannot be explained by current models, and that an intelligent designer must have created life or guided its evolution. Accordingly, the debate on irreducible complexity concerns two questions: whether irreducible complexity can be found in nature, and what significance it would have if it did exist in nature.
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 has a long history and can be traced back at least 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 by natural and sexual selection. The argument from irreducible complexity attempts to demonstrate that certain biological features cannot be purely the product of Darwinian evolution.
Possible examples
Behe and others, including some evolutionists, have suggested a number of biological features that they believe may be irreducibly complex.
The bombardier beetle
The bombardier beetle (genus Brachinus ) is an organism that has become a standard example of irreducible complexity among those who argue for it. These beetles have three chambers in their abdomen, two of which contain liquids that are chemically stable in isolation but react violently when mixed. The third chamber is a reaction chamber into which the two chemicals are squeezed when danger is near, and from which they are expelled explosively towards the perceived danger. Irreducible complexity asserts that, in order for any of the components of the system to function, all components of the system must have been present.
The bird lung
The bird lung is different from other lungs, such as the reptile lung (which evolutionists believe it evolved from). Proponents of irreducible complexity argue that the transition from a reptile lung (bellows lung ) to a bird lung (circulatory lung ) is unlikely since intermediate stages would be a detriment to the organism.
- Recently, conventional wisdom has held that birds are direct descendants of theropod dinosaurs. However, the apparently steadfast maintenance of hepatic-piston diaphragmatic lung ventilation in theropods throughout the Mesozoic poses a fundamental problem for such a relationship. The earliest stages in the derivation of the avian abdominal airsac system from a diaphragmatic-ventilating ancestor would have necessitated selection for a diaphragmatic hernia [i.e. hole] in taxa transitional between theropods and birds. Such a debilitating condition would have immediately compromised the entire pulmonary ventilatory apparatus and seems unlikely to have been of any selective advantage. (Michael Denton)
See Handicaps and Sexual Selection section below.
Flagella
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 causes the flagella to 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.
This topic is discussed in the article on the Evolution of flagella.
Certain biological pathways
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 blood clotting cascade in vertebrates is another complex biological pathway that is given as an example of irreducible complexity.
One evolutionary mechanism that may result in complex biological pathways such as these is "biochemical 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.
Other examples
In social and economic history
Apparent irreducible complexity is a phenomenon not confined to biology. In accounting for the reawakening of Europe in the 12th century and the rise of the towns, historian Fernand Braudel instances the demographic expansion that itself needs to be explained, the progress in agricultural techniques which began in the eleventh century with the improved design of the plough, triennial crop rotation and the open field system for stock farming, the progress made in trade, the spread of a money economy, agricultural over-production and the accumulation of surpluses... "All the explanations must in the end be combined," Braudel notes (in The Perspective of the World 1984, p. 95). "How could there have been any growth unless everything progressed at more or less the same pace? A larger population, the perfection of agricultural techniques, the revival of trade and the first wave of craft industry were all essential factors if the area known as Europe was to develop an urban network." And yet the historic renaissance of medieval Euriope is a fact.
Opposition
It may be that irreducible complexity does not actually 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. Thus they would either be merely very complex, or they would be misunderstood or misrepresented.
The precursors of complex systems, when they are not useful in themselves, may be useful to perform other, unrelated functions. Evolutionary biologists argue 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 considered classic examples.
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. By analogy, stone arches are irreducibly complex — if you remove any stone the arch will collapse — yet we build them easily enough, one stone at a time, by building over scaffolding that is removed afterward. Similarly, naturally occurring arches of stone are formed by weathering away bits of stone from a large concretion that has formed previously.
Behe has been accused of using an argument by lack of imagination, or constructing a "God of the gaps". Behe himself 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.
Gradual replacement
Arguments for irreducibility often assume that things started out the same way they ended up (as we see them now). However, that may not necessarily be the case.
Regarding Behe's antibody example, we have the "marker" substance and the "killer" substance, that together hunt and kill marked invaders. Behe is saying that by themselves, the marker and the killer are useless, and thus must have been made at the same time. The killer cannot kill what it cannot find and the marker has no ability to kill even if it can find a target.
However, under gradual replacement, a different marker may have started out as an independent hunter AND killer. After a while, a helper killer joined this army because it had some nice specialties. However, this second killer still depended on the first one to find the target. Thus the first killer served as both a marker and a killer, and the second killer is just a killer, relying on the first to hunt.
Perhaps over time it is more efficient to have the 2nd killer specialize in killing and the first specialize in marking, and so the first killer is replaced by a similar substance that is merely a marker (perhaps a better marker than the first dual-purpose one).
Thus, each step is an advantage, yet the final result is a dependent pair that does not resemble the proto-killer. This example can be laid out as:
- A = original killer and marker
- K = second killer
- M = replacement marker
- A
- AK
- AMK
- MK
All we see today is "MK". Opponents of irreducible complexity state that Behe erroneously assumes that if the structure ended up MK, then it must have started out as M or K by themselves.
Handicaps and Sexual Selection
Another overlooked source of "irreducibly complex" features in a sexually reproducing organism is the Handicap Theory. Sexual selection often favors those who can demonstrate to their mates a surplus of energy by maintaining a feature or behavior that is unnecessary for basic survival -- sometimes even a hinderance. Examples include certain horns and antlers, display feathers, skin or hair colors and patterns, bony structure, scents, songs, symmetry, and elaborate ritualistic behavior. It is not unreasonable to imagine a handicapping feature eventually developing a useful purpose in a changing environment or for two or more handicapping features to become useful when combined. Conversely, a useful feature may evolve to become a handicapping feature, but through sexual selection the feature is passed through generations to again become useful in a completely different context. In this new context it may seem impossible to us that it was naturally selected to its purpose.
Imagine that a spontaneous hole formed in a pre-bird lizard's lung and quickly became a demonstration to potental mates that it has "energy to burn" because it was successful despite its handicap. Perhaps it evolved as a mating display because it made a distinctive sound like a frog's mating display. That feature could have been maintained by sexual selection long enough to have evolved into the modern bird lung we see today.
Falsifiability and experimental evidence
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 are 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 take a different approach, 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 asserts is evidence that "Behe is wrong".
Significance (if found)
Behe argues that organs and biological features which are irreducibly complex cannot be wholly explained by current models of evolution. He argues that:
- 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.
Irreducible complexity is not an argument that evolution does not occur, but rather an argument that it is incomplete. If irreducible complexity is found and it cannot be wholly explained by current models of evolution, then, it is argued, alternative models may be considered such as:
External links
In support
In opposition
References
- Behe, Michael (1996). Darwin's Black Box. New York: The Free Press. ISBN 0684834936
- Denton, Michael (1996). Evolution: A Theory in Crisis. Adler & Adler.
- Ruben, J.A.; Jones, T.D.; Geist, N.R.; & Hillenius, W.J. (November 14, 1997). Lung Structure and Ventilation in Theropod Dinosaurs and Early Birds. Science 278 (5341) 1267–1270.
- Sunderland, Luther D. (March 1976). Miraculous Design in Woodpeckers. Creation Research Society Quarterly.
Last updated: 08-23-2005 19:38:56
