The Case for a Creator (33 page)

“First, there’s a flat wooden platform to which the other parts are attached. Second, there’s a metal hammer, which does the job of crushing the mouse. Third, there’s a spring with extended ends to press against the platform and the hammer when the trap is charged. Fourth, there’s a catch that releases when a mouse applies a slight bit of pressure. And, fifth, there’s a metal bar that connects to the catch and holds the hammer back when the trap is charged.

“Now, if you take away any of these parts—the spring or the holding bar or whatever—then it’s not like the mousetrap becomes half as efficient as it used to be or it only catches half as many mice. Instead, it doesn’t catch
any
mice. It’s broken. It doesn’t work at all.”

He pointed down at the trap again. “And notice that you don’t just need to have these five parts, but they also have to be matched to each other and have the right spatial relationship to each other. See—the parts are stapled in the right place. An intelligent agent does that for a mousetrap. But in the cell, who tells the parts where they should go? Who staples them together? Nobody—they have to do it on their own. You have to have the information resident in the system to tell the components to get together in the right orientation, otherwise it’s useless.”

Behe sat back down. “So the mousetrap does a good job of illustrating how irreducibly complex biological systems defy a Darwinian explanation,” he continued. “Evolution can’t produce an irreducibly complex biological machine suddenly, all at once, because it’s much too complicated. The odds against that would be prohibitive. And you can’t produce it directly by numerous, successive, slight modifications of a precursor system, because any precursor system would be missing a part and consequently couldn’t function. There would be no reason for it to exist. And natural selection chooses systems that are already working.”

I studied the mousetrap. “You said an irreducibly complex system can’t be produced
directly
by numerous, successive, slight modifications,” I said. “Does that mean there couldn’t be an indirect route?”

Behe shook his head. “You can’t absolutely rule out all theoretical possibilities of a gradual, circuitous route,” he said. “But the more complex the interacting system, the far less likely an indirect route can account for it. And as we discover more and more of these irreducibly complex biological systems, we can be more and more confident that we’ve met Darwin’s criterion of failure.”

I asked, “Are there a lot of different kinds of biological machines at the cellular level?”

“Life is actually based on molecular machines,” he replied. “They haul cargo from one place in the cell to another; they turn cellular switches on and off; they act as pulleys and cables; electrical machines let current flow through nerves; manufacturing machines build other machines; solar-powered machines capture the energy from light and store it in chemicals. Molecular machinery lets cells move, reproduce, and process food. In fact, every part of the cell’s function is controlled by complex, highly calibrated machines.”

Behe motioned toward the mousetrap. “And if the creation of a simple device like this requires intelligent design,” he said, “then we have to ask, ‘What about the finely tuned machines of the cellular world?’ If evolution can’t adequately explain them, then scientists should be free to consider other alternatives.”

Before I began investigating that issue any further, though, I wanted to stay focused a while longer on Behe’s whimsical use of the mousetrap to illustrate irreducible complexity. Ever since
Darwin’s Black Box
was published, the lowly rodent-catcher has become something of a new icon in the debate over evolution versus design. As such, it has been pelted by opposition from Darwinists—and I needed to know if Behe could fend off the best challenges.

MESSING WITH THE MOUSETRAP

“Your mousetrap has generated quite a bit of controversy,” I began. “For instance, John McDonald of the University of Delaware said mousetraps can work well with fewer parts than yours—and he even drew a picture of a trap that’s simpler than the one you drew. Doesn’t this undermine your point that your mousetrap is irreducibly complex?”

“No, not a bit,” he said with a good-natured smile. “I
agree
there are mousetraps with fewer parts than mine. As a matter of fact, I said so in my book! I said you can just prop open a box with a stick, or you can use a glue trap, or you can dig a hole for the mouse to fall into, or you can do any number of things.

“The point of irreducible complexity is not that one can’t make some other system that could work in a different way with fewer parts. The point is that the trap we’re considering right now needs all of its parts to function. The challenge to Darwinian gradualism is to get to my trap by means of numerous, successive, slight modifications. You can’t do it. Besides, you’re using your intelligence as you try. Remember, the audacious claim of Darwinian evolution is that it can put together complex systems with no intelligence at all.”

Behe’s simple explanation seemed sufficient to defeat McDonald’s critique.
⁶
But there was a stronger challenge to consider. I reached down into my briefcase and removed a copy of
Natural History
magazine. “Kenneth Miller of Brown University has another objection to your trap,” I said. Then I read him Miller’s comments:

Take away two parts (the catch and the metal bar), and you may not have a mousetrap but you do have a three-part machine that makes a fully functional tie clip or paper clip. Take away the spring, and you have a two-part key chain. The catch of some mousetraps could be used as a fishhook, and the wooden base as a paperweight; useful applications of other parts include everything from toothpicks to nutcrackers and clipboard holders. The point, which science has long understood, is that bits and pieces of supposedly irreducibly complex machines may have different—but still useful—functions.
⁷

“That’s a strong point,” I said. “Maybe an irreducibly complex system could develop gradually over time, because each of its components could have another function that natural selection would preserve on the way toward developing a more complex machine.”

“That’s an interesting argument,” he said.

I leaned forward. “Doesn’t this dismantle your case?” I asked.

Behe didn’t flinch. “The problem,” he replied, “is that it’s not an argument against anything I’ve ever said. In my book, I explicitly point out that some of the components of biochemical machines can have other functions. But the issue remains—can you use numerous, slight, successive modifications to get from those other functions to where we are?

“Some of this objection seems a bit silly. Could a component of a mousetrap function as a paperweight? Well, what do you need to be a paperweight? You need mass. You need to exist. An elephant, or my computer, or a stick can be a paperweight. But suppose you go buy a paperweight. What would it look like? Most of them are nondescript, roundish things. None of them look anything like a precursor to a mousetrap. Besides, look at what he’s doing: he’s starting from the finished product—the mousetrap—and disassembling it and moving a few things around to use them for other purposes. Again, that’s intelligent design!

“The question for evolution is not whether you can take a mousetrap and use its parts for something else; it’s whether you can start with something else and make it into a mousetrap. The problem for evolutionists is to start with a less complex system and build a more complex system. Even if every component could theoretically have a useful function prior to its assembly into the mousetrap, you’d still have the problem of how the mousetrap becomes assembled.”

“Explain further,” I said.

“When people put together a mousetrap, they have the disassembled components in different drawers or something, and they grab one from each drawer and put it together. But in the cell, there’s nobody there to do that.

“In molecular machines, components have portions of their shape that are complementary to each other, so they connect with each other in the right way. A positive charge can attract a negative charge, and an oily region can attract another oily region. So if we use the mousetrap as an analogy, one end of the spring would have to have a certain shape or magnetism that just happened to attract and fit with another component of the trap. They’d all have to fit together that way until you had the whole trap assembled by itself.

“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 together for this new function,” I said. “For instance, microtubules look a bit like girders. Maybe they were used in the structure of primitive cells. Or maybe they formed the cellular highways along which the motor proteins moved material within the cell.”

Behe didn’t look impressed. “A motor protein that has been transporting cargo along a cellular highway might not have the strength necessary to push two microtubules relative to each other,” he replied. “A nexin linker would have to be exactly the right size before it was useful at all. Creating the cilium inside the cell would be counterproductive; it would need to extend from the cell. The necessary components would have to come together at the right place at the right time, even assuming they were all pre-existing in the cell.”

“Isn’t it possible that they might all come together by chance?” I asked.

“It’s extraordinarily improbable,” he replied. “Let me illustrate it for you. Say there are ten thousand proteins in a cell. Now, imagine you live in a town of ten thousand people, and everyone goes to the county fair at the same time. Just for fun, everyone is wearing blindfolds and is not allowed to speak. There are two other people named Lee, and your job is to link hands with them. What are the odds that you could go grab two people at random and create a link of Lees? Pretty slim. In fact, it gets worse. In the cell, the mutation rate is extremely low. In our analogy, that would mean you could only change partners at the county fair one time a year.

“So you link with two other people—sorry, they’re not the other Lees. Next year, you link with two other people. Sorry, no Lees again. How long would it take you to link with the other Lees? A very, very long time—and the same is true in the cell. It would take an enormous amount of time—a
prohibitive
amount of time—even to get three proteins together.