Pushing Back the Test

Once Intelligent Design is shorn of its distracting attacks on evolution, there’s very little real science left to consider. How does Intelligent Design account for all of the evidence in favor of evolution, from the fossil record to mutation rates to the similarities and differences between species? At what exact point did the designer intervene in the evolution of the horse, or bird flight, or the Cambrian explosion? And what did the designer do? How can we test these claims? What predictions has Intelligent Design made that have resulted in important new discoveries? If you look for answers to these questions, you end up only with contradictions, untestable claims, or, most often, silence.

In 1996 Michael Behe attempted to make the case for Intelligent Design in Darwin’s Black Box. Behe, a biochemist at Lehigh University, presented some examples of complex biochemistry and declared that they could not have evolved. Yet at the same time, he granted that “on a small scale, Darwin’s theory has triumphed.” In other words, in the world of Intelligent Design, things do evolve: finches change the size of their beaks; HIV adapts to new hosts; birds introduced into the United States have diversified into new groups. But these sorts of small changes can’t produce the complexity of life.

The problem for Intelligent Design is that small changes add up to big effects. As time passes, mutations build up in the DNA of populations of animals and other organisms. Once enough small changes have amassed, populations can evolve into distinct species. Scientists can use the genetic differences to work out the relationships of these species. If Behe accepts microevolution, he has no choice but to accept the tree of life as well. (According to this tree, incidentally, humans are close cousins to chimpanzees. Creationists who don’t savor the idea that their ancestors were apes must recognize that Intelligent Design surrenders this point.) And since Behe offers no objection to the fossil record and isotopic dating, he apparently accepts that the tree of life has branched out over the course of the last 4 billion years.

So where does evolution stop and “design” begin? Hard to say. Did an Intelligent Designer step in 500 million years ago and install the clotting cascade in the earliest vertebrates? Did the designer step in 150 million years ago, when mammals evolved a complex set of molecules that allowed a placenta to implant itself into a mother’s uterus and prevent her immune system from rejecting a fetus? Or every time a species of milkweed has invented a new kind of poison to fight off insects? Behe never tells us.

Making matters even murkier, Behe even grants that some molecules don’t look designed. Hemoglobin, the molecule that carries oxygen in red blood cells, has a structure remarkably like myoglobin, an oxygen‑storing molecule in our muscles. Behe therefore says that hemoglobin is not a good example of Intelligent Design. “The behavior of hemoglobin can be achieved by a rather simple modification of the behavior of myoglobin,” he writes. But myoglobin–now, that has to be irreducibly complex, according to Behe, because he cannot conceive how it could have evolved.

By muddling its claims with evolution, Intelligent Design cannot create hypotheses that can be tested. If I propose that a molecule is irreducibly complex and evidence emerges that it could have evolved by gene duplication or some other process, I can write it off as a product of evolution and move the whole argument back to the earlier molecule. Behe himself toys with pushing Intelligent Design all the way back to the very beginning of life’s history. He speculates that the first cell might have been designed with all the complex networks of genes that were used later in different organisms. Different kinds of organisms continued to use certain genes, while others were silenced.

“This notion leaves so much of molecular evolution unexplained that it’s hard to know where to start,” says H. Allen Orr, a biologist at the University of Rochester. It is true that some genes do get silenced over time. A gene may get duplicated, for example, and one of the copies mutates until it can’t make a protein. These useless genes are known as pseudogenes. But the pseudogenes we carry, Orr points out, resemble our own active genes. If Behe were correct, you’d expect to find pseudogenes in our DNA that looked like the active genes in all sorts of other species. Why don’t we carry pseudogenes for making rattlesnake venom or flower petals? Why do we instead share so many pseudogenes with chimpanzees?

Evolution offers a straightforward explanation: only after our own ancestors diverged from those of flowers and rattlesnakes did these pseudogenes evolve. Intelligent Design, on the other hand, can claim only that it just so happened that silenced genes were silenced the way they were. As with previous versions of creationism, Intelligent Design leaves us with a designer who goes to enormous lengths to trick us into thinking that life evolved.

Intelligent Design fails because it abandons the central quest of science. “If you’re allowed just to postulate something complicated enough to design a universe intelligenfly, then you’ve sold the past,” says Richard Dawkins. “You’ve simply allowed yourself to assume the existence of exactly the thing which we’re trying to explain. The beauty of the theory of evolution by natural selection is that it starts with simple things, and it builds up slowly and gradually to complex things, including things complex enough to design things–brains, in other words. If you allow yourself to use the idea of design right from the start, then you are simply giving up the beginning. You’re simply not providing any kind of explanation at all.”