The phrase irreducible complexity has reluctantly entered the working vocabulary of evolutionary biologists, though they usually disparage its source (Dr. Michael Behe, leading proponent of intelligent design). The latest evidence is a paper in Science that was titled with an obvious play on words and an attempt to refute Behe’s principle. They called it “irremediable complexity.” 
The team of biologists from Canada and the Czech Republic neither referenced Behe’s book nor mentioned his name, but it is clear they wanted to refute his thesis that complex molecular machines require intelligent design. “Many of the cell’s macromolecular machines appear gratuitously complex, comprising more components than their basic functions seem to demand,” they said. “How can we make sense of this complexity in the light of evolution?” As examples, they produced the spliceosome and ribosome, structures they claim have “Seemingly gratuitous complexity”. From the gratuitous, they invoked the fortuitous, in a somewhat circuitous manner. By chance, they said, two independent bodies might become connected. As additional mutations occur, it becomes more difficult for them to separate than to remain interdependent. That’s the reason for their phrase “irremediable complexity” – there’s no going back. The result is a kind of “ratchet” mechanism that increases complexity and interdependence, but not necessarily adaptation: “Thus, constructive neutral evolution is a directional force that drives increasing complexity without positive (and in small populations, against mildly negative) selection,” they explained. “Negative selection is involved, but only as the stabilizing force that keeps this directionality from reversing.” 
How, then, does adaptation occur? The ribosome and spliceosome, after all, are tremendously effective machines despite their complexity, gratuitous or not. The authors seem to say that the function must have been already been present before the complexity accumulated:
Although compensation for defects caused by “selfish” (self-propagating) DNA elements may seem intuitive, it is problematic to propose that, on the way to evolving compensatory machinery, an intermediate state had to exist that was less fit than its ancestors and sisters. Why would such an intermediate not just die out in competition before its rescue by compensatory complexity yet to be invented? A more workable model is that the compensating mechanism was already present (possibly serving unrelated functions).
They were thus trying to solve one problem with evolutionary theory (adaptationism) by introducing another – a kind of “pre-adaptation” inherent in the machinery that turned on when the circumstances needed it. This ratchet model, called “constructive neutral evolution,” they claimed, “provides an explanatory counterpoint to the selectionist or adaptationist views that pervade molecular biology.” To support their model, therefore, they had to take issue with the vast majority of evolutionists who support Neo-Darwinism.
In the end, though, this was all about refuting Michael Behe’s claim that molecular machines illustrate intelligent design:
Although this model is easiest to illustrate using molecular systems of peripheral importance or limited distribution (such as splicing or RNA editing), there is no reason why it might not contribute to the generation of any cellular complexity (the ribosome; mitochondrial respiratory complexes; light-harvesting antennae in photosynthetic organisms; RNA and DNA polymerases and their initiation, elongation, and termination complexes; protein import, folding, and degradation apparatuses; the cytoskeleton and its motors). Much of the bewildering intricacy of cells could consist of originally fortuitous molecular interactions that have become more or less fixed by constructive neutral evolution. Indeed, although complexity in biology is generally regarded as evidence of “fine tuning” or “sophistication,” large biological conglomerates might be better interpreted as the consequences of runaway bureaucracy—as biological parallels of nonsensically complex Rube Goldberg machines that are over-engineered to perform a single task.
Readers of Behe’s Darwin’s Black Box (Free Press, 1996) might recall that on p. 75 he reproduced a Rube Goldberg cartoon as an illustration of irreducible complexity.
1. Michael W. Gray, Julius Lukes, John M. Archibald, Patrick J. Keeling, W. Ford Doolittle, “Irremediable Complexity?”, Science, 12 November 2010: Vol. 330. no. 6006, pp. 920-921, DOI: 10.1126/science.1198594.
2. In evolutionary theory, positive selection means increased fitness, whereas negative selection removes deleterious mutations. Stabilizing selection works to keep things running in place with neither progress nor regress.