Darwin's Black Box

The Biochemical Challenge to Evolution

Michael J. Behe

• Publisher: Free Press
• Year: 2001
• ISBN:
  9780743214858
• Topic: Ciencias biológicas
• Subtopic: Ciencias en general

The groundbreaking, "seminal work" ( Time ) on intelligent design that dares to ask, was Darwin wrong? In 1996, Darwin's Black Box helped to launch the intelligent design movement: the argument that nature exhibits evidence of design, beyond Darwinian randomness. It sparked a national debate on evolution, which continues to intensify across the country. From one end of the spectrum to the other, Darwin's Black Box has established itself as the key intelligent design text—the one argument that must be addressed in order to determine whether Darwinian evolution is sufficient to explain life as we know it.In a major new Afterword for this edition, Behe explains that the complexity discovered by microbiologists has dramatically increased since the book was first published. That complexity is a continuing challenge to Darwinism, and evolutionists have had no success at explaining it. Darwin's Black Box is more important today than ever.

PART I

CHAPTER 1

THE LIMITS OF AN IDEA

This book is about an idea—Darwinian evolution—that is being pushed to its limits by discoveries in biochemistry. Biochemistry is the study of the very basis of life: the molecules that make up cells and tissues, that catalyze the chemical reactions of digestion, photosynthesis, immunity, and more.¹ The astonishing progress made by biochemistry since the mid-1950s is a monumental tribute to science’s power to understand the world. It has brought many practical benefits in medicine and agriculture. We may have to pay a price, though, for our knowledge. When foundations are unearthed, the structures that rest on them are shaken; sometimes they collapse. When sciences such as physics finally uncovered their foundations, old ways of understanding the world had to be tossed out, extensively revised, or restricted to a limited part of nature. Will this happen to the theory of evolution by natural selection?

Like many great ideas, Darwin’s is elegantly simple. He observed that there is variation in all species: some members are bigger, some smaller, some faster, some lighter in color, and so forth. He reasoned that since limited food supplies could not support all organisms that are born, the ones whose chance variation gave them an advantage in the struggle for life would tend to survive and reproduce, outcompeting the less favored ones. If the variation were inherited, then the characteristics of the species would change over time; over great periods, great changes might occur.

For more than a century most scientists have thought that virtually all of life, or at least all of its most interesting features, resulted from natural selection working on random variation. Darwin’s idea has been used to explain finch beaks and horse hoofs, moth coloration and insect slaves, and the distribution of life around the globe and through the ages. The theory has even been stretched by some scientists to interpret human behavior: why desperate people commit suicide, why teenagers have babies out of wedlock, why some groups do better on intelligence tests than other groups, and why religious missionaries forgo marriage and children. There is nothing—no organ or idea, no sense or thought—that has not been the subject of evolutionary rumination.

Almost a century and a half after Darwin proposed his theory, evolutionary biology has had much success in accounting for patterns of life we see around us. To many, its triumph seems complete. But the real work of life does not happen at the level of the whole animal or organ; the most important parts of living things are too small to be seen. Life is lived in the details, and it is molecules that handle life’s details. Darwin’s idea might explain horse hoofs, but can it explain life’s foundation?

Shortly after 1950 science advanced to the point where it could determine the shapes and properties of a few of the molecules that make up living organisms. Slowly, painstakingly, the structures of more and more biological molecules were elucidated, and the way they work inferred from countless experiments. The cumulative results show with piercing clarity that life is based on machines—machines made of molecules! Molecular machines haul cargo from one place in the cell to another along “highways” made of other molecules, while still others act as cables, ropes, and pulleys to hold the cell in shape. Machines turn cellular switches on and off, sometimes killing the cell or causing it to grow. Solar-powered machines capture the energy of photons and store it in chemicals. Electrical machines allow current to flow through nerves. Manufacturing machines build other molecular machines, as well as themselves. Cells swim using machines, copy themselves with machinery, ingest food with machinery. In short, highly sophisticated molecular machines control every cellular process. Thus the details of life are finely calibrated, and the machinery of life enormously complex.

Can all of life be fit into Darwin’s theory of evolution? Because the popular media likes to publish exciting stories, and because some scientists enjoy speculating about how far their discoveries might go, it has been difficult for the public to separate fact from conjecture. To find the real evidence you have to dig into the journals and books published by the scientific community itself. The scientific literature reports experiments firsthand, and the reports are generally free of the flights of fancy that make their way into the spinoffs that follow. But as I will note later, if you search the scientific literature on evolution, and if you focus your search on the question of how molecular machines—the basis of life—developed, you find an eerie and complete silence. The complexity of life’s foundation has paralyzed science’s attempt to account for it; molecular machines raise an as-yet-impenetrable barrier to Darwinism’s universal reach. To find out why, in this book I will examine several fascinating molecular machines, then ask whether they can ever be explained by random mutation/natural selection.

Evolution is a controversial topic, so it is necessary to address a few basic questions at the beginning of the book. Many people think that questioning Darwinian evolution must be equivalent to espousing creationism. As commonly understood, creationism involves belief in an earth formed only about ten thousand years ago, an interpretation of the Bible that is still very popular. For the record, I have no reason to doubt that the universe is the billions of years old that physicists say it is. Further, I find the idea of common descent (that all organisms share a common ancestor) fairly convincing, and have no particular reason to doubt it. I greatly respect the work of my colleagues who study the development and behavior of organisms within an evolutionary framework, and I think that evolutionary biologists have contributed enormously to our understanding of the world. Although Darwin’s mechanism—natural selection working on variation—might explain many things, however, I do not believe it explains molecular life. I also do not think it surprising that the new science of the very small might change the way we view the less small.

A VERY BRIEF HISTORY OF BIOLOGY

When things are going smoothly in our lives most of us tend to think that the society we live in is “natural,” and that our ideas about the world are self-evidently true. It’s hard to imagine how other people in other times and places lived as they did or why they believed the things they did. During periods of upheaval, however, when apparently solid verities are questioned, it can seem as if nothing in the world makes sense. During those times history can remind us that the search for reliable knowledge is a long, difficult process that has not yet reached an end. In order to develop a perspective from which we can view the idea of Darwinian evolution, over the next few pages I will very briefly outline the history of biology. In a way, this history has been a chain of black boxes; as one is opened, another is revealed.

Black box is a whimsical term for a device that does something, but whose inner workings are mysterious—sometimes because the workings can’t be seen, and sometimes because they just aren’t comprehensible. Computers are a good example of a black box. Most of us use these marvelous machines without the vaguest idea of how they work, processing words or plotting graphs or playing games in contented ignorance of what is going on underneath the outer case. Even if we were to remove the cover, though, few of us could make heads or tails of the jumble of pieces inside. There is no simple, observable connection between the parts of the computer and the things that it does.

Imagine that a computer with a long-lasting battery was transported back in time a thousand years to King Arthur’s court. How would people of that era react to a computer in action? Most would be in awe, but with luck someone might want to understand the thing. Someone might notice that letters appeared on the screen as he or she touched the keys. Some combinations of letters—corresponding to computer commands—might make the screen change; after a while, many commands would be figured out. Our medieval Englishmen might believe they had unlocked the secrets of the computer. But eventually somebody would remove the cover and gaze on the computer’s inner workings. Suddenly the theory of “how a computer works” would be revealed as profoundly naive. The black box that had been slowly decoded would have exposed another black box.

In ancient times all of biology was a black box, because no one understood on even the broadest level how living things worked. The ancients who gaped at a plant or animal and wondered just how the thing worked were in the presence of unfathomable technology. They were truly in the dark.

The earliest biological investigations began in the only way they could—with the naked eye.² A number of books from about 400 B.C. (attributed to Hippocrates, the “father of medicine”) describe the symptoms of some common diseases and attribute sickness to diet and other physical causes, rather than to the work of the gods. Although the writings were a beginning, the ancients were still lost when it came to the composition of living things. They believed that all matter was made up of four elements: earth, air, fire, and water. Living bodies were thought to be made of four “humors”—blood, yellow bile, black bile, and phlegm—and all disease supposedly arose from an excess of one of the humors.

The greatest biologist of the Greeks was also their greatest philosopher, Aristotle. Born when Hippocrates was still alive, Aristotle realized (unlike almost everyone before him) that knowledge of nature requires systematic observation. Through careful examination he recognized an astounding amount of order within the living world, a crucial first step. Aristotle grouped animals into two general categories—those with blood, and those without—that correspond closely to the modern classifications of vertebrate and invertebrate. Within the vertebrates he recognized the categories of mammals, birds, and fish. He put most amphibians and reptiles in a single group, and snakes in a separate class. Even though his observations were unaided by instruments, much of Aristotle’s reasoning remains sound despite the knowledge gained in the thousands of years since he died.

Only a few significant biological investigators lived during the millennium following Aristotle. One of them was Galen, a second-century A.D. physician in Rome. Galen’s work shows that careful observation of the outside and (with dissection) the inside of plants and animals, although necessary, is not sufficient to comprehend biology. For example, Galen tried to understand the function of animal organs. Although he knew that the heart pumped blood, he could not tell just from looking that the blood circulated and returned to the heart. Galen mistakenly thought that blood was pumped out to “irrigate” the tissues, and that new blood was made continuously to resupply the heart. His idea was taught for nearly fifteen hundred years.

It was not until the seventeenth century that an Englishman, William Harvey, introduced the theory that blood flows continuously in one direction, making a complete circuit and returning to the heart. Harvey calculated that if the heart pumps out just two ounces of blood per beat, at 72 beats per minute, in one hour it would have pumped 540 pounds of blood—triple the weight of a man! Since making that much blood in so short a time is clearly impossible, the blood had to be reused. Harvey’s logical reasoning (aided by the still-new Arabic numerals, which made calculating easy) in support of an unobservable activity was unprecedented; it set the stage for modern biological thought.

In the Middle Ages the pace of scientific investigation quickened. The example set by Aristotle had been followed by increasing numbers of naturalists. Many plants were described by the early botanists Brunfels, Bock, Fuchs, and Valerius Cordus. Scientific illustration developed as Rondelet drew animal life in detail. The encyclopedists, such as Conrad Gesner, published large volumes summarizing all of biological knowledge. Linnaeus greatly extended Aristotle’s work of classification, inventing the categories of class, order, genus, and species. Studies of comparative biology showed many similarities between diverse branches of life, and the idea of common descent began to be discussed.

Biology advanced rapidly in the seventeenth and eighteenth centuries as scientists combined Aristotle’s and Harvey’s examples of attentive observation and clever reasoning. Yet even the strictest attention and cleverest reasoning will take you only so far if important parts of a system aren’t visible. Although the human eye can resolve objects as small as one-tenth of a millimeter, a lot of the action in life occurs on a micro level, a Lilliputian scale. So biology reached a plateau: One black box, the gross structure of organisms, was opened only to reveal the black box of the finer levels of life. In order to proceed further biology needed a series of technological breakthroughs. The first was the microscope.

BLACK BOXES WITHIN BLACK BOXES

Lenses were known in ancient times, and by the fifteenth century their use in spectacles was common. It was not until the seventeenth century, however, that a convex and a concave lens were put together in a tube to form the first crude microscope. Galileo used one of the first instruments, and he was amazed to discover the compound eyes of insects. Stelluti looked at the eyes, tongue, antennae, and other parts of bees and weevils. Malpighi confirmed the circulation of the blood through capillaries and he described the early development of the embryonic chick heart. Nehemiah Grew inspected plants; Swammerdam dissected the mayfly; Leeuwenhoek was the first person ever to see a bacterial cell; and Robert Hooke described cells in cork and leaves (although their importance escaped him.)

The discovery of an unanticipated Lilliputian world had begun, overturning settled notions of what living things are. Charles Singer, the historian of science, noted that “the infinite complexity of living things thus revealed was as philosophically disturbing as the ordered majesty of the astronomical world which Galileo had unveiled to the previous generation, though it took far longer for its implications to sink into men’s minds.” In other words, sometimes the new boxes demand that we revise all of our theories. In such cases, great unwillingness can arise.

The cell theory of life was finally put forward in the early nineteenth century by Matthias Schleiden and Theodor Schwann. Schleiden worked primarily with plant tissue; he argued for the central importance of a dark spot—the nucleus—within all cells. Schwann concentrated on animal tissue, in which it was harder to see cells. Nonetheless he discerned that animals were similar to plants in their cellular structure. Schwann concluded that cells or the secretions of cells compose the entire bodies of animals and plants, and that in some way the cells are individual units with a life of their own. He wrote that “the question as to the fundamental power of organized bodies resolves itself into that of individual cells.” As Schleiden added, “Thus the primary question is, what is the origin of this peculiar little organism, the cell?”

Schleiden and Schwann worked in the early to middle 1800s—the time of Darwin’s travels and the writing of The Origin of Species. To Darwin, then, as to every other scientist of the time, the cell was a black box. Nonetheless he was able to make sense of much biology above the level of the cell. The idea that life evolves was not original with Darwin, but he argued it by far the most systematically, and the theory of how evolution works—by natural selection working on variation—was his own.

Meanwhile, the cellular black box was steadily explored. The investigation of the cell pushed the microscope to its limits, which are set by the wavelength of light. For physical reasons a microscope cannot resolve two points that are closer together than approximately one-half of the wavelength of the light that is illuminating them. Since the wavelength of visible light is roughly one-tenth the diameter of a bacterial cell, many small, critical details of cell structure simply cannot be seen with a light microscope. The black box of the cell could not be opened without further technological improvements.

In the late nineteenth century, as physics progressed rapidly, J. J. Thomson discovered the electron; the invention of the electron microscope followed several decades later. Because the wavelength of the electron is shorter than the wavelength of visible light, much smaller objects can be resolved if they are “illuminated” with electrons. Electron microscopy has a number of practical difficulties, not least of which is the tendency of the electron beam to fry the sample. But ways were found to get around the problems, and after World War II electron microscopy came into its own. New subcellular structures were discovered: Holes were seen in the nucleus, and double membranes detected around mitochondria (a cell’s power plants). The same cell that looked so simple under a light microscope now looked much different. The same wonder that the early light microscopists felt when they saw the detailed structure of insects was again felt by twentieth-century scientists when they saw the complexities of the cell.

This level of discovery began to allow biologists to approach the greatest black box of all. The question of how life works was not one that Darwin or his contemporaries could answer. They knew that eyes were for seeing—but how, exactly, do they see? How does blood clot? How does the body fight disease? The complex structures revealed by the electron microscope ...

Table of contents

• Cover Page
• Title Page
• Contents
• Preface
• Part I: The Box is Opened
• Part II: Examining The Contents of The Box
• Part III: What Does The Box Tell Us?
• Appendix: The Chemistry of Life
• Notes
• Acknowledgments
• Copyright Page