Proponents of intelligent design have long argued that “specified complexity” is a reliable indicator of design. An event or pattern can be said to exhibit specified complexity if it (a) is exceedingly improbable (factoring in the relevant probabilistic resources); and (b) conforms to some independently given pattern. Unlike a random assembly of alphabetic and punctuation characters (which exhibits complexity), the sentences and paragraphs in this (or any) article exhibit what ID theorists call “specified complexity.” That is to say, the sequences of characters are organized in a particular way to convey meaning to people who are acquainted with the English language. ID proponents argue that specified complexity uniformly arises from intelligent causes, not the unguided forces of nature.
From time to time, I encounter the rather bizarre claim that the concept of specified complexity is a meaningless one — that one cannot objectively distinguish mere “Shannon information” (which correlates directly with reduced uncertainty) from what ID theorists call “complex and specified information.” I have found that there are two very good rejoinders to this argument that, without fail, shut down the objection quickly. Since this objection comes up often on the Internet, I thought that this would be a good place to share these rejoinders.
First, if specified complexity is a meaningless concept, why is the “chance” hypothesis uniformly and unanimously rejected as a viable explanation for both the origins of life and for biological evolution? Indeed, caricatures of the theory of evolution that suggest that it is driven by chance processes alone are routinely repudiated by materialists and quite rightly so. If there was no fundamental difference between mere “complexity” and “specified complexity,” then why not invoke just chance? Random processes, after all, can produce rather a lot of complexity — even things that are astronomically improbable. The precise course of events that has elapsed since the beginning of the universe (some 13.7 billion years ago) is astronomically improbable. But no one for a moment would think that this fact alone demonstrates design. After all, some astronomically improbable series of events had to happen.
The second problem with objecting to specified complexity is that most or all of the arguments for common ancestry are in fact based on reasoning from specified complexity. The discovery of precisely the same improbable evolutionary events (e.g. parallel point mutations or mobile element integration) in multiple lineages begs for explanation. If the complex event in question occurred independently in each of the separate lineages, then it would constitute specified complexity, and thus be suggestive of some kind of teleology. Thus, the most parsimonious explanation from a materialist standpoint — i.e. that the event in fact only happened once and each of the lineages subsequently inherited the resultant changes from a common ancestor — is favored.
The critics of specified complexity are, it seems to me, being inconsistent on this point.