We’ve had a creationist named “biasevolution” babbling away in the comments. He’s not very bright and he’s longwinded, always a disastrous combination, and he tends to echo tedious creationist tropes that have been demolished many times before. But hey, I’m indefatigable, I can hammer at these things all day long.

He brings up irreducible complexity (IC), Behe’s ever-popular contribution to the creationism debate. Behe’s version of the idea was published in 1996, so we’ve had almost 20 years to refute it — successfully! — so it gets a little old seeing it brought up again and again.

If you really, really understood IC you WOULD NOT argue with it. You would find that it would be as silly as say arguing against variation or heredity, or the principle of flotation. The reason is this: if you must design a system towards some given function or set of function you would need critical parts. For one, you must have a source of energy for that system. Two, it must have a set of interacting parts that work towards the function you want, you can even add parts to fine-tune it to better perform that function (eg adding capacitors to fans to smoothen out voltage reduced). To then argue that an eye ain’t IC is laughable. All the accounts supposedly falsifying IC or showing how it evolved routinely assume simple IC precursors or point to other IC systems lacking a part and say IC is refuted for a system as Miller did in the blood clotting cascade (akin to arguing because some cars don’t use clutches cars ain’t IC).

I do understand IC quite well. I’ve read Behe’s books. I’ve had it thrown in my face many times, often by creationists who don’t understand it (Jerry Bergman’s claim that carbon all by itself is irreducibly complex was particularly memorable). Biasevolution’s version isn’t quite that bad, but it’s still awful.

And it’s wrong.

First, there’s the problem of begging the question: if you must design a system towards some given function. You’re trying to argue that something is designed, and the first thing you do is demand that we accept the premise that it is designed?

The whole point of the IC concept is that if you examine a final ‘design’, and there’s no way to remove a piece of the structure without destroying its function, then it could not have evolved in a stepwise fashion, as evolution would predict. That’s really all it says: that evolution is falsified if you identify a pathway, for instance, that would not be functional if you removed a piece. It’s naively appealing — but only if you think evolutionary change must be symmetrical and reversible. But we actually evolve irreducibly complex systems all the time.

Let’s work through a simple example. Here’s a pathway, or circuit: a battery, a switch, and a light bulb (I’ve left out the one wire to complete the circuit, just to simplify it all; don’t take it too literally.) You close the switch, the bulb lights up. Simple.

Here’s a simple expansion of that circuit. I’ve merely duplicated the switch, so now there’s two of them: close either one, the bulb lights up. This might not be a trivial change to an electrician, but it is to a geneticist — genes get duplicated all the time, and typically all it would do is add a redundant element. So this is a routine variation of a kind that is frequently observed in biological systems.

Now we change one wire, shifting the output of the first switch from directly activating the effector (the bulb) to feeding into the second switch. Now to light up the bulb, you must close the second switch, but the first switch is redundant.

The biological analog to this would be if, for instance, a protein in a biochemical pathway lost its ability to bind a terminal substrate, but could still activate an intermediate protein. Again, this happens.

Now you could imagine a mutation that destroyed the first switch, and the whole system would simply revert to the initial condition, in which a single switch controls the bulb. That happens, too — we find dead genes (called pseudogenes) all over the genome.

Or, just as possible, what if you kept the first switch but lost another wire?

This is an interesting change. Now, to light up the bulb, you have to close both the first and second switch. It also fits Behe’s description of an irreducibly complex system, because removing any part, the battery, the first switch, or the second switch, produces a pathway that cannot light up the bulb. It’s a dead system. It is most definitely irreducibly complex by any reading of Behe’s hypothesis.

But does that mean it could not have evolved by the incremental addition or subtraction of parts, with every step retaining the full capability of lighting up the bulb? Of course not. I just led you through each step, and in all four of the cartoons above, you can turn the lightbulb on. The fact of ICness does not vitiate the idea of incremental evolution.

So naive creationists will look at the fact of the organization of the eye, that you cannot remove the optic nerve or the retina and still have a functional eye, and fallaciously argue that that means it could not have evolved. This is logically false. I can point to lots of biological systems that can be called irreducibly complex: I am personally irreducibly complex, for instance, because I would stop functioning if you cut out my heart or gave me a brainectomy or deleted a big chunk of my immune system — but that fact is not sufficient to demonstrate that evolution couldn’t have done it.

I’ve been pointing this out to creationists for well over a decade, and all I ever get from them is stupefied stares and the occasional splutter. I don’t expect it will sink in this time, either. But I do derive a certain rude satisfaction from the fact that creationists repeatedly exhibit that same dumb incomprehension every time, so I’ll keep puncturing them with it.