Jerry A. Coyne is a professor emeritus in the Department of Ecology and Evolution at the University of Chicago. He is the author of “Why Evolution is True” and “Faith vs. Fact: Why Science and Religion are Incompatible.”

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The notion of “intelligent design” arose after opponents of evolution repeatedly failed on First Amendment grounds to get Bible-based creationism taught in the public schools. Their solution: Take God out of the mix and replace him with an unspecified “intelligent designer.” They added some irrelevant mathematics and fancy biochemical jargon, and lo: intelligent design, which scientists have dubbed “creationism in a cheap tuxedo.”

But the tuxedo is fraying, for intelligent design has been rejected not just by biologists but also by judges who recognize it as poorly disguised religion. Nevertheless, its advocates persist. Among the most vocal is Michael J. Behe, a biology professor at Lehigh University whose previous books, despite withering criticism from scientists, have sold well in a country where 76 percent of us think God had some role in human evolution.

Behe does not rely on the Bible as a science textbook. Rather, he admits that evolution occurs by natural selection sifting new mutations and that all species are related via common ancestors. Where he parts company with other biologists is in his claim that the important mutations producing new types of organisms are not random accidents but are deliberately installed by a designer with a plan. A pious Catholic, Behe sees the designer as the Christian God but concedes that there could be other mutation-makers. These designed mutations solve what he sees as a problem for natural selection: the origin of some complex biochemical features. Such features appear to defy Darwinian explanation because, claims Behe, they can’t function until all the parts are in place. (Unguided natural selection requires that every step in the evolution of a complex feature must enhance an organism’s fitness.) Ergo, these “irreducibly complex” systems must have been forged by a designer who made simultaneous changes in several genes.


Scientists, however, were quick to spot the obvious errors in this argument. First, they pointed out numerous scenarios in which a system fitting Behe’s definition of “irreducible complexity” could evolve in a step-by-step manner (one is the hormone pathway studied by my Chicago colleague Joe Thornton). They then adduced clear evidence from many complex biochemical systems that these scenarios had actually occurred. Indeed, the uniform experience of scientists who work on these systems is that they embody an absurd, Rube Goldberg-like complexity that makes no sense as the handiwork of an engineer but makes perfect sense as a product of a long and unguided historical process.

Further, Behe’s rationale for designed mutations is circular. He claims that biochemical pathways are designed rather than evolved because they’re based on the “purposeful arrangement of parts.” But which arrangements are those designed with a purpose? They’re simply the pathways that Behe sees as too complex to have evolved. This is a classic example of begging the question: assuming what you’re supposed to prove (purposefulness). Yet the history of science is replete with natural phenomena like electricity and infectious disease that were once imputed to God simply because we didn’t understand them. The lesson that Behe and his intelligent-design supporters should learn is that in the face of scientific ignorance, it’s more productive to keep working than to punt to God as the solution.

Perhaps Behe’s most ludicrous claim is this: Evolution within the lowest levels of biological classification — genera and species — might be purely Darwinian, but the origin of higher-level groups — families, orders and so on — requires designed mutations. Yet as every biologist knows, groupings above the level of species are purely subjective. That is, whether you call a group a family or a genus is arbitrary, depending on the tastes of the scientists who work on that group. For example, a given difference in a trait like color or size might help define a new family of birds but only a new genus of frogs (ornithologists tend to be “splitters” while herpetologists are often “lumpers”). This arbitrariness means there’s no reason to suppose that the bird mutations are designed while the frog ones are natural and random. To make things worse, Behe gives not a single example of a family-level mutation that he thinks required the help of a creator.

Behe’s third attack on evolution is that, even at lower levels, it’s “self-limiting.” That is, two features of evolution — its reliance on random mutations and on natural selection — make the process eventually wind down, preventing further change and requiring the designer to step in. Both of these claims are wrong.

Mutation supposedly acts as a brake on evolution because, argues Behe, most genes that fuel adaptation have been irreparably broken and inactivated by mutations (a gene that doesn’t do anything can still be better than one making an unneeded product). And a dead gene, because it tends to degrade further, can’t easily be reactivated. Evolution, then, must eventually grind to a halt.

Behe selectively gives a handful of examples in which mutations have produced broken genes that are nevertheless useful, but he simply ignores the large number of adaptive mutations that do not inactivate genes. These include duplications, in which a gene is accidentally copied twice, with the copies diverging in useful ways (this is how primates acquired our three-color vision, as well as different forms of hemoglobin); changes not in gene function but in how and when a gene is turned on and off, like mutations producing lactose tolerance in milk-drinking human populations; the repurposing of ancient genes acquired from viruses (one source of the mammalian placenta); “chimeric genes” cobbled together from odd bits of DNA (e.g., genes producing antifreeze proteins in fish blood ); and simple changes in DNA sequence that alter proteins without breaking them (tolerance of low oxygen levels in high-flying geese). As long as a substantial number of genetic mutations don’t break genes, which seems to be the case, evolution can work just fine.

Behe also argues that evolution is self-limiting because natural selection “adjust[s] a biological system to its current function” and thus “works to block the system from taking up a significantly different function.” But environments change and current functions become outmoded, prompting new evolution. And new adaptations can fortuitously create new niches: Think of how feathers, which probably evolved to conserve body heat in dinosaurs, opened up the possibility of flight — leading to all the diverse birds on Earth.

Like his creationist kin, Behe devotes his time not to giving evidence for intelligent design but to attacking evolutionary biology. As Herbert Spencer said, “Those who cavalierly reject the Theory of Evolution, as not adequately supported by facts, seem quite to forget that their own theory is supported by no facts at all.” But Behe’s theory, promulgated by the Discovery Institute, Seattle’s intelligent-design organization, does demand support. Who, exactly, is the designer, and what evidence is there that this designer makes nonrandom mutations? Is the designer an immaterial god, in which case we need to know how this god violates the laws of physics by causing mutations, or is the designer material, like a space alien, in which case we must understand the physical methods whereby aliens change our DNA?

And what is an example of a designed mutation? (Behe is silent here.) Since humans are placed in the same family as other great apes (Hominidae), Behe’s theory predicts that we arose without a designer’s intervention. But here he backpedals, asserting that there are “excellent reasons to suspect those differences [between humans and other apes] are well beyond Darwinian processes.” Sadly, he doesn’t give these reasons, but I’d guess they stem from the Christian belief that Homo sapiens is a special creation of God. Such ad hoc claims, derived from religion, explain why intelligent design has been deemed by the courts as “a mere re-labeling of creationism, and not a scientific theory.”

In 1998, the Discovery Institute drafted the “Wedge Document,” a secret plan (leaked in 1999) to spread Christianity in America by teaching intelligent design and fighting materialism. One of the plan’s 20-year goals was “to see intelligent design theory as the dominant perspective in science.” Well, now it’s 20 years on, and despite the efforts of Behe and other neo-creationists, intelligent design has been discredited as science and outed as disguised religion. It’s no surprise, then, that “Darwin Devolves” was published by HarperOne, the religious, spiritual and self-help division of HarperCollins.

Darwin Devolves
The New Science About DNA That Challenges Evolution

By Michael J. Behe

HarperOne. 342 pp. $28.99