“If man can by patience select variations useful to him, why, under changing and complex conditions of life, should not variations useful to nature’s living products often arise, and be preserved or selected? What limit can be put to this power, acting during long ages and rigidly scrutinising the whole constitution, structure, and habits of each creature,—favoring the good and rejecting the bad? I can see no limit to this power, in slowly and beautifully adapting each form to the most complex relations of life. The theory of natural selection, even if we look no farther than this, seems to be in the highest degree probable.”

The products of human selection surround us. From the ubiquitous species we have modified for food, to our domestic pets and decorative plants, we have ingeniously developed much of our organic environment. By hybridizing and crossbreeding the variations we discovered in natural populations, we have reengineered organisms to meet both our needs and our whims. It is no surprise that Charles Darwin began what he called his “one long argument” for natural selection with so clear evidence of the malleability of species. His proposal of “descent with modification” stated simply that the process of selection would, over time, create new species distinct and separate from the original. Unlike human selection, which operates with certain ends in mind, the success of natural selection is driven by fitness: those that are best suited to the environment are likely to leave more offspring.

Darwin believed that the slow, gradual work of “survival of the fittest” would change species bit by bit. He believed that evidence of these incremental changes would eventually be found in the fossil record. Indeed, a few “missing links” or transitional forms have been unearthed, but the problem of incremental change remains one of the theory’s greatest challenges.

This is not a newly discovered difficulty. While the concept of punctuated equilibrium has for the most part replaced the gradualist view of evolution, an inability to believe that small variations enhance the survival and reproductive potential of individuals fuels ongoing criticism. Even if change occurred quickly, must there not have been a time when individuals derived benefit from sporting half a wing, a partly developed eye, or the rudimentary beginnings of a male-female reproductive system?

In the late 1800s, when science was more a gentlemen’s activity than an academic profession, novelist Samuel Butler pointed to related difficulties in his book Life and Habit (1877): “If the differences between an elephant and a tadpole-like fish have arisen from the accumulation of small variations that have had no direction given them by intelligence and sense of needs, then no time conceivable by man would suffice for their development.”

The Argument Continues

This problem of how blind processes of evolution create new species and biological systems through small steps is also addressed in two recent books.

In The Plausibility of Life: Resolving Darwin’s Dilemma, Marc Kirschner and John Gerhart ask, “Could they [complex structures with specific complex functions: eyes, hearts, wings, etc.] have been plausibly assembled, small piece by small piece, each presupposing a selective advantage?” Kirschner, of Harvard Medical School, and Gerhart, of the University of California–Berkeley, believe they have uncovered the way nature creates variations that are finished products rather than stages on the way to completion. They argue that they have solved the bit-by-bit dilemma by uncovering a mechanism that can show “how random genetic change is converted into useful innovation.”

Michael Behe, in The Edge of Evolution: The Search for the Limits of Darwinism, speaks to the same bit-by-bit problem. He calls this difficulty of unfinished steps “irreducible complexity.” Behe, of Lehigh University, became the poster boy for Intelligent Design after the 1996 publication of his previous book, Darwin’s Black Box. There he wrote, “To a person who does not feel obliged to restrict his search to unintelligent causes, the straightforward conclusion is that many biochemical systems were designed.” As his new title implies, he believes that while natural selection can explain many things about life on earth, random mutation and selection have been “grossly oversold to the modern public” as a solution for the planet’s biodiversity. “Most mutations that built the great structures of life must have been nonrandom.”

Randomness

Darwin did not invent the evolutionary worldview; he merely offered (along with his contemporary Alfred Wallace) a mechanism through which biological adaptation could occur. The system he proposed, however, insisted that variation and natural selection worked blindly and without forethought or intention. Prior to Origin of Species, the prevailing theory of evolution had been of change driven by need, as alluded to by Butler above, or the aspiration of all life toward higher or ideal forms.

Although no one of that period understood the source of variation as we do today (the genetic code), nor how an organism functions at the cellular level (the control of gene expression), the impetus for evolution was believed to be within each organism. Imagining such an internal drive offered some comfort and sensibility. It implied that all living things had a responsible part to play in their own success and adaptation as well as in their connection and interaction with other individuals.

Although even Darwin succumbed to inventing a physiologic system whereby an organism’s life experiences could be packaged and passed on to the next generation, he remained dedicated to the random and purposeless nature of evolution. The concept of natural selection was then and remains today a disruptive idea; it leaves everything to be arbitrated by chance. Chance rolls out variations randomly, and the environment selects those that are best fit to survive and pass on their traits to the next generation.

This idea that nature is a “blind watchmaker”—that undirected natural processes can, on their own, create complexity—is both the core of modern evolutionary theory and at the heart of why the theory feels so uncomfortable to many. To understand what these two new texts have added to the discourse, it is helpful to understand that these authors are not working with new questions or controversies.

Origin or Genesis?

Admitting in Origin the difficulty of expecting “extremely slight and gradual” changes to come together to create so complex a structure as the vertebrate eye, Darwin noted: “I have felt the difficulty far too keenly to be surprised at others hesitating to extend the principle of natural selection to so startling a length.” Then he added the statement which has become the challenge of many a critic over the last century: “If it could be demonstrated that any complex organ existed, which could not possibly have been formed by numerous, successive, slight modifications, my theory would absolutely break down. But I can find out no such case.”

Darwin included these comments in his sixth edition of Origin, in response to St. George Mivart’s critical text, On the Genesis of Species. A naturalist like Darwin, Mivart argued that “natural selection utterly fails to account for the conservation and development of the minute and rudimentary beginnings, the slight and infinitesimal commencements of structures, however useful those structures may afterwards become.” Focusing briefly on insects that mimic plants (for example, katydids and walking sticks), Mivart continued that to end up with such biological structure “out of utterly indifferent and indeterminate infinitesimal variations in all conceivable directions” appears impossible.

Darwin’s critics were looking for something, just as they do today, that showed evolution had purpose. Few people doubted the idea of change in the late 1800s, but the idea of change without purpose, without the directing power of a Creator, was just not acceptable. But of course, as we know, Darwin held his ground: “Variability is governed by many unknown laws, of which correlated growth is probably the most important. . . . To adapt a species to new habits of life, many co-ordinated modifications are almost indispensable.”

Plausible Answers?

Kirschner and Gerhart begin where Darwin left off. How can novel, directionless variations add up to complexity? “Ignorance about novelty,” they offer, “is at the heart of skepticism about evolution, and resolving its origins is necessary to complete our understanding of Darwin’s theory.”

Outlining what they call “evolvability,” the authors conclude that life is indeed plausible by natural selection if the results of random mutation are biased toward useful variation. Their hypothesis is called “facilitated variation.” It is based on the observation that all living things share the same basic biochemistry and cell structure. This commonality, all the way up from genetic code to protein structure to embryological development, is evidence of the building process of natural selection, they believe.

The authors argue that this uniformity has only the appearance of design and planning. Using human design of clocks as a model of what “intelligent design” must look like (William Paley’s famous discovered brass watch takes center stage in their discussion, which bookends the introduction and conclusion of the text), Kirschner and Gerhart describe the many ways in which intelligent humans solve a single problem. The “evolution” of keeping time created the hourglass, wristwatch, grandfather clock and atomic clock, for example; all do the same job but are completely different machines. There is no commonality of mechanism.

From this they assert that living things do not show design, as the same mechanism is used over and over by seemingly unrelated organisms. If living things were the work of a Creator, they ask, wouldn’t each organism be unique, built from its own particular and idiosyncratic plan? On the other hand, as Darwin astutely observed, “have we any right to assume that the Creator works by intellectual powers like those of man?”

Kirschner and Gerhart insist that what looks like intelligence—conserving and using the same system in a variety of ways—is actually the result of life having evolved a way to channel random mutation toward nonrandom ends: “The bias introduced by facilitated variation accelerates the process of natural selection by giving it more viable variation of a type likely to be appropriate to the selective conditions than it would have been if variation occurred in all directions.”

Summing up Darwinian theory as “genetic variation, phenotypic variation, and selection,” Kirschner and Gerhart posit that while genes may vary randomly, the phenotypic or body changes that can actually result from these mutations are directional, a rearrangement of modules creating a greater variety of possibly useful variations rather than a disorganized mess of “not quites” or “halfway theres.” They write, “Novelty in the organism’s physiology, anatomy, or behavior arises mostly by the use of conserved processes in new combinations, at different times, and in different places and amounts, rather than by the invention of new processes.”

“The novelty and the complexity of the [prokaryotic] cell is so far beyond anything inanimate in the world today that we are left baffled by how it was achieved.”

The origin of these “conserved processes” remains unanswered. Where and how did these common traits first arise? “There is really no alternative but to think that new core processes, such as those that first arose in eukaryotic cells, were cobbled together from the existing processes in prokaryotic cells.” Unfortunately, this is where the solution to Darwin’s dilemma sputters to a halt: “The novelty and the complexity of the [prokaryotic] cell is so far beyond anything inanimate in the world today that we are left baffled by how it was achieved. . . . We can do little more than speculate.”

Another View of Design

According to Michael Behe, Kirschner and Gerhart have just reached the twilight zone of evolutionary biology, the edge of Darwinism. The problem, Behe agrees, is random mutation, but he also believes that the source code on which mutation can operate is not beyond speculation. He wants to find “the line between the random and the nonrandom that defines the edge of evolution.” That line is drawn exactly where facilitated variation begins: the core biochemical processes common to all life.

In this sense the three authors are seeking to answer the same question that challenged Darwin regarding Origin: How does variation work? Behe is, at the most basic level, attempting to place purpose back into evolution: “As Darwin thought, life descended with modification from one stage to another. Mutations arose in a long series—but many were not random.” Common descent is true but trivial, Behe believes. “It says merely that commonalities were there from the start, present in a common ancestor. It does not even begin to explain where those commonalities came from, or how humans subsequently acquired remarkable differences. Something that is nonrandom must account for the common descent of life” (Behe’s emphasis).

While Kirschner and Gerhart would call this nonrandomness “facilitated variation” at best, or even leave it on the shelf for another day, Behe attributes it to the intervention of a supernatural hand. “The bottom line is that, while great progress has been made toward understanding how animals are made, and has revealed unexpected, stunning complexity, no progress at all has been made in understanding how that complexity could evolve by unintelligent processes.”

“For a bevy of reasons having little to do with science, this crucial aspect of Darwin’s theory—the power of natural selection coupled to random mutation—has been grossly oversold to the modern public.”

Countering the plausibility argument, Behe returns to irreducible complexity. Assured that complex systems require multiple coherent steps to be created, he repeats that “without the intimate involvement of a directing intelligence, [mutations] would not come about in nature.” This does not mean that natural selection is invalid. Behe spends much of his book showing where selection is not over the edge, particularly with diseases. In this, he says, natural selection may certainly work with what already exists. Kirschner and Gerhart concur: “Mutation only changes what already exists. It does not create new anatomy, physiology, and behavior from nothing.”

Looking for a Sign

Like taking sides for candidates of opposing parties, loyalists find no value in their favorite’s adversary. Thus it is unfortunate that few party-line Darwinists would be interested in The Edge of Evolution and few IDers in The Plausibility of Life. Both texts are valuable; each gives the reader new insights into the state of evolutionary science as well as clear explanations of how living things function. To simply play one against the other, to join one camp and ignore the other side’s argument, is myopic.

Science is defined as materialist. Thus it will never buckle to the concept of intelligent selection. Nor will it agree that any of the complexities of nature are evolutionarily irreducible. From the scientific perspective, the answer to complexity will always be natural selection and other random factors; the mere existence or fact of a thing—an eye, a chemical pathway, a beautiful turn of color—will always trump irreducibility. The scientific method cannot accept a nonmaterial basis for any theory; this is not how scientific endeavor proceeds.

That does not mean, however, that nonscientific perspectives are invalid. Behe suggests that it is foolish to believe that scientific method is the final arbiter of all questions of natural form and behavior. “The beginning of life needed a directing intelligence,” he insists. Such tenacity does not make his position true either, of course. But neither should it be ignored because it is beyond the pale. Unconventional thinkers such as Behe often move the conversation forward in unlikely ways.

But even Behe is careful to walk softly when claiming the necessity of a causative agent to implement what he finds otherwise biologically impossible: “The idea of intelligent design, although congenial to some religious views of the universe, is independent of them. . . . One can’t leap directly from design to a transcendent God.”

Darwinism is certainly flawed; it has been revised and revised again as new information concerning the nature of life has come to light over the past century and a half. This is no surprise, nor does it mean the idea of evolution is a house of cards ready to implode. Facilitated variation is a new revision. Will it stand up to future scrutiny? While Behe does not believe so, one cannot discredit Kirschner’s and Gerhart’s efforts to compile in one place the immense evidence of a commonality of life on earth.

For the biologist, realizing this deep unity among living things may be the most unexpected discovery science has made in the last few decades. For Behe and others, it is really not surprising in the least; the conservation of complex systems across all life is a most obvious sign of intelligence at work.