The Case for a Creator - Lee Strobel [108]
“In other words, if you just had the components themselves without the ability to bring the other pieces into position, you’d be far from having a functioning mousetrap. Nobody ever addresses this problem in the evolutionary literature. If you do any calculations about how likely this could occur by itself, you find it’s very improbable. Even with small machines, you wouldn’t expect them to self-assemble during the entire lifetime of the earth. That’s a severe problem that evolutionists don’t like to address.”
THE AMAZING, MOVING CILIUM
The mousetrap emerged unscathed. But of course, it was only intended to be an illustration to help people understand irreducibly complex cellular systems. I decided to press forward by asking about some specific examples of molecular machines to see whether they could have developed by the step-by-step evolutionary process envisioned by Darwin. When I asked Behe for a specimen of irreducible complexity, he quickly cited the cilium.
“Cilia are whiplike hairs on the surface of cells. If the cell is stationary, the cilia move fluid across the cell’s surface. For instance,” he said, pointing toward my throat, “you’ve got cilia lining your respiratory tract. Every cell has about two hundred of them, and they beat in synchrony in order to sweep mucus toward your throat for elimination. That’s how your body expels little foreign particles that you accidentally inhale. But cilia also have another function: if the cell is mobile, the cilia can row it through a fluid. Sperm cells would be an example; they’re propelled forward by the rowing action of cilia.”
“That sounds fairly simple,” I remarked.
“That’s what scientists used to think when they examined cilia under a light microscope. They just looked like little hairs. But now that we have electron microscopes, we’ve found that cilia are, in fact, quite complicated molecular machines. Think about it: most hairs don’t beat back and forth. What enables cilia to do this? Well, it turns out a cilium is made up of about two hundred protein parts.”
“How does it function?”
He smiled. “I’ll try to keep this basic,” he said. “There are nine pairs of microtubules, which are long, thin, flexible rods, which encircle two single microtubules. The outer microtubules are connected to each other by what are called nexin linkers. And each microtubule has a motor protein called dynein. The motor protein attaches to one microtubule and has an arm that reaches over, grabs the other one, and pushes it down. So the two rods start to slide lengthwise with respect to each other. As they start to slide, the nexin linkers, which were originally like loose rope, get stretched and become taut. As the dynein pushes farther and farther, it starts to bend the apparatus; then it pushes the other way and bends it back. That’s how you get the rowing motion of the cilium.
“That doesn’t begin to do justice to the complexity of the cilium. But my point is that these three parts—the rods, linkers, and motors—are necessary to convert a sliding motion into a bending motion so the cilium can move. If it weren’t for the linkers, everything would fall apart when the sliding motion began. If it weren’t for the motor protein, it wouldn’t move at all. If it weren’t for the rods, there would be nothing to move. So like the mousetrap, the cilium is irreducibly complex.”
“Why can’t Darwinian evolution account for that?”
“You only get the motion of the cilium when you’ve got everything together. None of the individual parts can do the trick by themselves. You need them all in place. For evolution to account for that, you would have to imagine how this could develop gradually—but nobody has been able to do that.”
I ventured a possibility. “Maybe these three components were being used for other purposes in the cell and eventually came