Tag Archives: “Mullerian Two-Step”

Irreducibly Complex Bridges

20100703-bridges7This week, I want to take a break from the series on defining Christian terminology to look at something from the talkorigins website that an atheist friend sent me a while back claiming to show how Michael Behe’s term “irreducible complexity” (IC hereafter) is “plainly silly” using an example of a stone bridge. If you’re not familiar with any of this, Michael Behe wrote a book in 1996 called “Darwin’s Black Box”, questioning evolutionary theory and proposing that some observed biological systems defy evolutionary explanation because they are “irreducibly complex”. Behe has defined this term as “a single system which is necessarily composed of several well-matched, 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.”[1]

Think of an engine stripped down of all unnecessary parts. You can’t remove parts like the pistons, the spark plugs, the crankshaft, etc, without making the system nonfunctional. The theory of evolution rests on functioning (specifically, self-replicating) organisms reacting to unguided mutations and subject to natural selection to filter the resulting set for specimens with improved survivability. But natural selection doesn’t work on a nonfunctional system as there’s no improvement to select for. Appeals to “neutral evolution” where a mutation doesn’t have to have an actual benefit are just an appeal to chance, which is already stacked against evolution as most random mutations are harmful.[2] In our engine example, this means that adding a crankshaft to some cylinders won’t fulfill any function that could allow the engine to survive while the other parts like pistons and spark plugs are being gradually added. If you’ve ever had some daunting DIY repairs to do on your own car, you know there are some repairs where you can replace one component each night after work and still get to work the next morning while the overall repair is in progress, and then there are those long weekend projects where the car will be “dead” until the repair is completely done. An IC system is likewise dead until it’s complete.

Now, with that background, the talkorigins site has an interesting critique of Michael Behe’s idea of “irreducible complexity” where the author suggests that a “Mullerian Two-Step” defeats Behe’s entire argument. Is this “Mulllerian Two-Step” a dance move named after scientist H.J. Muller? Well, kind of – it does sidestep the key issue. In the words of the talkorigins author, “Only two basic steps are needed to gradually evolve an irreducibly complex system from a functioning precursor: 1) Add a part. 2) Make it necessary. It’s that simple. After these two steps, removing the part will kill the function, yet the system was produced directly and gradually from a simpler, functional precursor.”[3] The author’s argument is that a bridge composed of 3 stones may have a topping stone added, which does not add any functionality to the bridge, allowing the removal of the original middle stone, making the added topping stone necessary to the function of the bridge (see the illustration from the talkorigins page below).

Mullers Stone Bridge Allegedly, this proves that an irreducibly complex structure can be developed from piecewise addition of parts in accord with evolutionary theory. Yet, if you notice, the original 3 stone bridge in his example is already irreducibly complex. No single stone can be removed from his “functional precursor” without destroying it’s function. All 3 stones are required to be in place and working together to have a passable bridge. So what does this devastating argument actually prove? Simply that one irreducibly complex structure can be transformed into another irreducibly complex structure with stepwise, evolution-like steps. This does nothing to explain away the original irreducible complexity, which is the core objection to unguided evolution.

When you see atheist claims to destroy/devastate Christianity (or anything else opposed to a materialistic worldview, such as Intelligent Design/Irreducible Complexity), step back and carefully look at a) the assumptions, b) the connections between premises, and c) the conclusions, and you’ll likely find the claims of obvious superiority exaggerated. Whether you subscribe to Behe’s arguments or not, this “Mullerian Two-Step” is based on a flawed foundational assumption that the precursor is functional but not irreducible also. Therefore, it simply isn’t a valid defeater for Behe’s theory.  Next contestant?

[1] Behe, M.J. 2004. “Irreducible Complexity: Obstacle to Darwinian Evolution.” In Debating Design: from Darwin to DNA, Ruse, M. and Dembski, W.
See footnote 2 of the talkorigins article for an admission of this inconvenient truth from H.J. Muller himself: “…for this reason we should expect very many, if not most, mutations to result in lethal factors ….” Other scientists have made similar admissions, and, of course, our own experiences of diseases like cancer seem to confirm this daily.
[3] http://www.talkorigins.org/faqs/comdesc/ICsilly.html, accessed 2015/03/03.