The Pony Fish's Glow

PREFACE AND ACKNOWLEDGMENTS

The subtitle of this book might just as well have been The Adaptationist Program, which would have informed biologists of its subject matter. The one I chose was inspired by George Gaylord Simpson, a distinguished student of fossil mammals and one of the giants of twentieth-century biology. In January 1947 he gave an address at Princeton University, “On the Problem of Plan and Purpose in Nature,” an expanded version of which was published the following June in The Scientific Monthly. I have no idea how either was received at the time, but I do know that they have been neglected ever since. I did not learn about them until 1965, despite many years of persistent interest in the topic and immense admiration for the author. When I finally came across it, I found the article to be, as expected, a superbly reasoned and gracefully presented review of earlier work, and a thorough demolition of much of the muddled thinking that was still prevalent on the topic of adaptation.

But I was not wholly satisfied with Simpson’s treatment of biological adaptations, for which he found plan and purpose appropriately descriptive. He discussed the mechanisms by which organisms solve the problems of life, which do indeed seem well planned and for obvious purposes, but there is more to the problem of plan and purpose than that. The adaptations of organisms also show gross deficiencies in their basic plans. I hope that this book gives a balanced perspective, showing both the power and the limitations of the evolutionary process.

I am grateful to Cambridge University Press for permission to reprint the figure on page 26 and to Oxford University Press for the one on page 140. William Yee of the State University of New York at Stony Brook drew the pigeons pictured on page 23. The final form of that figure and most of the others was produced by Karen Henrickson of Stony Brook.

Many people gave generously of their time and effort in helping with the writing. My wife, Doris Calhoun Williams, deserves special thanks for valuable advice on the entire text, and whatever accuracy can be found in the endnotes can be credited to her. Helena Cronin also read the whole work and offered many helpful criticisms and suggestions. Margie Profet read and gave detailed advice on the first five chapters and offered much discussion helpful for the final four. Michael Ruse helped immensely with the first and last chapters. None of these good friends will be surprised that I did not always follow their advice.

INTRODUCTION

PLAN AND PURPOSE IN NATURE

Most of us have an intuitive and adequate understanding of plan and purpose in man-made objects. The question “What is the purpose of a pencil?” need never be posed. A pencil’s size, shape, material composition, and a long list of other features conform closely to an ideal design for a writing instrument. Calling it a writing instrument summarizes these descriptive details without committing us to any belief about the origin or history of pencils. They could have been invented by Rube Goldberg or by a Neanderthal. We tend to have the same attitudes about the purpose of human body parts. The idea that our ears are for hearing, for example, can be shared by people who disagree on how or when the human ear acquired its admirable design as an auditory instrument.

I am sure that pencils had a complex evolution from a crude beginning, and that changes over the centuries arose from two sources: human imagination and human experience. Imaginative inventors proposed that some modifications might be improvements, and they tried them out. The changes that really turned out to be improvements were selected for manufacture and use; those that did not were discarded and forgotten. In this way pencils evolved by a combination of prior plan and subsequent selection based on trial and error.

A modern biologist recognizes no element of prior plan in the origin and evolution of the human ear. Ears and other features of living organisms, like the photophore of the pony fish discussed in chapter 1, are perfected entirely by the trial-and-error process of natural selection proposed by Charles Darwin in 1859. Ears are maintained and improved because individuals with better ears are more likely to survive and pass their genes on to future generations. This conclusion is supported by evidence that organisms can have sophisticated adaptations and at the same time show design features that would not be there if intelligent planning had played a role (see especially chapters 1, 3, 8, and 9). The idea that human adaptations arose entirely from blind trial and error has serious implications for any honest view of human nature and the present human condition (chapters 6 to 9).

In this book I assume the validity of what has been called the adaptationist program in recent technical literature. For each attribute of an organism, the program’s practitioners raise the question: How does this relate to the organism’s efforts to survive and pass on its genes? Such a question about human teeth, for example, has an obvious answer: they play a positive role in human nutrition, which is clearly needed for survival and reproduction. But the answer is less obvious with a more specific question: Why are there four incisors in each jaw? Serviceable dentitions with three or five incisors can easily be imagined. The answer may be purely historical: primates early in their history gradually changed from some larger number to four, and all primates today are stuck with it because there is no easy way to evolve from four to three or five.

Another question might be, What is the purpose of the sounds we make when gnawing bones or biting celery? The answer: none. Noise is an unavoidable cost of the use of such mechanical adaptations as human teeth. The scientific value of any of these answers is that they have implications that can be checked. They sometimes enable us to predict and make important discoveries. I hope that the early chapters of this book provide abundant justification for this claim.

The idea that theories about prior history can be predictive is often casually dismissed. This is because people think of prediction in terms of future history, when the important use of theory is to predict the outcome of investigations. This is nicely illustrated by a great triumph of nineteenth-century science, the discovery of Neptune. Two scientists independently in France and England, using observed anomalies in the orbit of the planet Uranus, predicted that a detailed examination of a certain part of the sky would reveal a previously unknown planet. When they carried out the investigation and found the planet, this was not the prediction of a future planet, or of any future event, but merely a prediction of what would be found when and if certain actions were carried out.

The same is true of theories of human history, as illustrated by the celebrated (and controversial) discovery of Troy. A story conceived from Homeric epics and classical scholarship inspired a theory by the amateur archaeologist Heinrich Schliemann. He proposed that if he made a certain kind of investigation at a site near the western end of the Dardanelles, he would find remains of the legendary city of Troy. He carried out this investigation in the 1870s and verified his prediction. So Schliemann’s theory, a narrative history with a specific geography, led to a discovery of great interest. This is routinely true of the theoretical stories told by evolutionary biologists.

The first five chapters of this book summarize my view of what the study of biological adaptation is like today. An adaptation is, by definition, something functionally effective that arises from the long-continued action of natural selection. A good example is the special light of a pony fish, an admirably sophisticated aid for solving an immensely important problem. But look more closely at that fish. It has only two eyes; would it not make better sense, from a functional perspective, for it to have more than that? Its mouth and pharynx do a strange kind of double duty: they serve for both feeding and respiration. Why should the respiratory and digestive systems be associated? There is, in fact, a good reason for them not to be associated: the double-duty pharynx makes it possible for pony fish, and vertebrates in general, to choke on food.

And what proportion of the pony fish population would you expect to be male? I expect that most readers, like most biologists, expect the answer to be close to half. Yet surely the population’s reproduction would be more efficient if only a minor fraction were male. These functionally onerous products of pony fish evolution deserve equal time with the functionally adaptive, and I hope that this book achieves something of the needed balance. The unfortunate aspects of evolution are emphasized in my final four chapters, which discuss their implications for contemporary human life—social, medical, and philosophical.

A book this size can give only the sketchiest outline of both current understandings and their implications. I hope that the endnotes will lead the more ambitious readers to other works that can elaborate on what is only outlined here.

CHAPTER 1

ADAPTATIONIST STORYTELLING

Consider the following pair of propositions: the Sun exists to illuminate the surface of the Earth; we have eyes to enable us to make use of the sunlight. Both statements imply a cause-effect relationship. The Sun is a cause of periodic brightness on the Earth’s surface, and eyes cause vision in animals that have them. Both also imply something more: that the Sun is there to fulfill a need for terrestrial illumination, and that we have eyes because we need to see. The point of this chapter is that the first of these further implications is false, or at least has no evidence in its support, and that the second is true, in a special and immensely important sense.

An examination of the Earth-Sun system utterly fails to support the idea that the sun exists to serve the planet. The sun is about 150 million kilometers away, a distance of nearly 12,000 Earth diameters. The Earth is nearly spherical and about 12,600 kilometers in diameter. Why would something that exists to serve the Earth be so far away from it? And why would it be enormously larger than what it is there to serve?

The Sun’s diameter is about 100 times that of the Earth, its volume roughly a million times greater. The whole gigantic surface of the Sun is brilliantly radiating in all directions. The Earth’s small size and great distance enable it to intercept less than a billionth of the Sun’s light. The rest radiates out in other directions, with other bodies in the solar system also intercepting minuscule proportions of it. The efficiency of the Sun’s use of energy in illuminating the Earth is microscopic. Indeed, a detailed examination of the Sun fails to disclose any features that relate specifically to the Earth.

What should we expect of a system really designed to illuminate the Earth? Given the constraint of having to use a single radiating sphere as the light source, we might want to economize on energy and materials by making the light source much smaller than the Earth but in a close circular orbit around it. This was the standard conception in antiquity, for example, the Greeks’ solar chariot crossing the sky from east to west. Even though this system’s efficiency might be a million times what we now have, it would still be low from an engineering perspective. Most of the light would miss the Earth and go off in other directions. With a precisely shaped and brightly polished reflector mounted behind the Sun, we could make do with a much weaker source and achieve an efficiency to satisfy rather stringent engineering demands.

But why the constraint of a spherical light source radiating in all directions? Why not have the Earth surrounded by a grid of fluorescent tubes, or something analogous on a colossal scale, with the tubing backed up by precisely shaped reflectors? Or you could have the light produced by terrestrial objects, like the two brilliant Trees of Valinor that for long ages furnished all needed light in J. R. R. Tolkien’s Middle Earth from leaves that shone from their undersides. Any such engineered light source would clearly show, by its obvious engineering, that lighting the Earth was its raîson d’être. The real Earth-Sun system shows no such evidence of purposive engineering.

What about the eye? This in fact is the classic example of plan and purpose in nature. It forms a centerpiece for William Paley’s version of the theological “argument from design” in his renowned early-nineteenth-century book Natural Theology:

Observe a new-born child first lifting up its eyelids. What does the opening of the curtain discover? The anterior part of two pellucid globes, which, when they come to be examined, are found to be constructed upon strict optical principles; the self-same principles upon which we ourselves construct optical instruments. We find them perfect for forming an image by refraction composed of parts executing different offices; one part having fulfilled its office upon a pencil of light, delivering it over to the action of another part; that to a third, and so onward; the progressive action depending for its success upon the nicest and minutest adjustment of the parts concerned; yet these parts so in fact adjusted, so as to produce, not by a simple action or effect, but by a combination of actions and effects, the result which is ultimately wanted. And forasmuch as this organ would have to operate under different circumstances, with strong degrees of light, and with weak degrees, upon near objects, and upon remote ones; and these differences demanded, according to the laws by which the transmission of light is regulated, a corresponding diversity of structure; that the aperture, for example, through which the light passes, should be larger or less; the lenses rounder or flatter, or that their distance from the tablet, upon which the picture is delineated, should be shortened or lengthened: This, I say, being the case, and the difficulty to which the eye was to be adapted, we find its several parts capable of being occasionally changed, and a most artificial apparatus provided to produce that change. This is far beyond the common regulator of a watch, which requires the touch of a foreign hand to regulate it; but it is not altogether unlike Harrison’s contrivance for making a watch regulate itself, by inserting within it a machinery, which, by the artful use of the different expansion of metals, preserves the equality of the motion under all the various temperatures of heat and cold in which the instrument may happen to be placed. The ingenuity of this last contrivance has been justly praised. Shall, therefore, a structure which differs from it, chiefly by surpassing it, be accounted no contrivance at all? or, if it be a contrivance, that it is without a contriver?

Modern physiologists would be entirely in agreement with Paley’s description of the structure and regulatory capabilities of the human eye, and would be able to add further facts in support of Paley’s reasoning. He well understood the eye as an optical instrument, up to the point of the formation of a precise two-dimensional image on the retina. Today we have, in addition, a detailed knowledge of retinal photochemistry and the way photic reactions in the rods and cones are efficiently transduced into nerve impulses. We partly understand the routing of these impulses through layer upon layer of information-processing machinery in the retina itself and then in the brain, so as to achieve the maximum possible amount of useful information from the light that reaches our eyes.

But what of Paley’s final question? Must a contrivance have a contriver? His asking it makes clear that he assumed only one possible answer. This is the point of his famous parable about finding a watch on the ground. Examining the watch showed it to be an elaborate contrivance for telling time. There must therefore have been a contriver (watchmaker) who understood the need to measure the passage of time and knew how to contrive a way to meet that need. For Paley, a Christian clergyman, there must be an eyemaker, the omniscient creator recognized by Judeo-Christian theology.

A CLOSER LOOK AT PALEY’S ARGUMENT

Unfortunately for this aspect of Paley’s reasoning, not all features of the human eye make functional sense. Some are arbitrary. To begin at the grossest level, is there a good functional reason for having two eyes? Why not one or three or some other number? Yes, there is a reason: two is better than one because they permit stereoscopic vision and the gathering of three-dimensional information about the environment. But three would be better still. We could have our stereoscopic view of what lies ahead plus another eye to warn us of what might be sneaking up behind. (I have more suggestions for improving human vision in chapter 7.) When we examine each eye from behind, we find that there are six tiny muscles that move it so that it can point in different directions. Why six? Properly spaced and coordinated, three would suffice, just as three is an adequate number of legs for a photographer’s tripod. The paucity of eyes and excess of their muscles seem to have no functional explanation.

And some eye features are not merely arbitrary but clearly dysfunctional. The nerve fibers from the retinal rods and cones extend not inward toward the brain but outward toward the chamber of the eye and source of light. They have to gather into a bundle, the optic nerve, inside the eye, and exit via a hole in the retina. Even though the obstructing layer is microscopically thin, some light is lost from having to pass through the layer of nerve fibers and ganglia and especially the blood vessels that serve them. The eye is blind where the optic nerve exits through its hole. The loose application of the retina to the underlying sclera makes the eye vulnerable to the serious medical problem of detached retina. It would not be if the nerve fibers passed through the sclera and formed the optic nerve behind the eye. This functionally sensible arrangement is in fact what is found in the eye of a squid and other mollusks (as shown in the figure below), but our eyes, and those of all other vertebrates, have the functionally stupid upside-down orientation of the retina.

Paley did not really confront this problem. Little was known about mollusks’ eyes at the time, and Paley merely treated the blind spots as one of the problems the eye must solve. He correctly noted that the medial position of the optic nerve exits avoids having both eyes blind to the same part of the visual field. Everything in the field is seen by at least one eye. It might also be claimed that the obstructing tissues of the retina are made as thin and transparent as possible, so as to minimize the shading of the light-sensitive layer. Unfortunately there is no way to make red blood cells transparent, and the blood vessels cast demonstrable shadows.

What might Paley’s reaction have been to the claim, which I will elaborate in the next chapter, that mundane processes taking place throughout living nature can produce contrivances without contrivers, and that these processes produce not only functionally elegant features but also, as a kind of cumulative historical burden, the arbitrary and dysfunctional features of organisms?

A. The human eye as it ought to be, with a squidlike retinal orientation. B. The human eye as it really is, with nerves and vessels traversing the inside of the retina.

OTHER EXAMPLES OF FUNCTIONAL DESIGN

The hand is another good example of the concept of functional design. The contraction of muscles in your forearm can lead to functionally precise actions by your hand because of an elaborate system of tendons slipping through well-lubricated channels in the wrist and hand and attaching to the functionally appropriate locations on each finger bone. The opposable thumb is one of the key adaptations that led to the human mastery of tool making and manipulation. And note the fingernails: their location, their shapes, and their mechanical properties. The Roman philosopher Galen wrote a superb treatise on the human hand and other body parts, and argued forcefully for its precision and effectiveness as an instrument for manipulation. He maintained that it was so perfect for this role that it was impossible to think of any change that would improve it. Perhaps he should thus be recognized as the originator of the optimization concept prominent in contemporary biology.

To Galen and Paley and most scholars prior to Darwin, the functional design of living organisms led inescapably to the conclusion that there must be a wise creator who designed the organisms and their many well-engineered parts. This line of reasoning ignores an important point in analogies like that between eye and camera. Cameras surely have designers—people wise in optics and mechanics and photochemistry and perhaps economics. Yet George Eastman did more than merely design cameras on the basis of his admirable understanding. He also tried them out, tested variations in design to determine what really worked well and what less well, even if he did not always understand why. Progress in photography depended not only on engineers’ understandings, but also on the data they gathered in laboratory and field tests.

What would Paley’s reaction have been to the suggestion that the creator’s wisdom is as finite as ours, and that the engineering perfection of such instruments as the eye and the hand depends, like the camera, on much trial-and-error tinkering that supplemented the creator’s limited understanding? And what about the suggestion that the creator had no understanding at all, but accomplished sophisticated engineering entirely on the basis of trial and error? This is essentially what is implied by modern Darwinism, as discussed in the next chapter.

The role of trial and error in the engineering of the devices that we make and use is perhaps more clearly illustrated by something simpler than a camera. Consider, for example, a fishhook. Archaeologists have found fishhooks that date from the Old Stone Age, perhaps as much as fifty thousand years ago. The early specimens were carved from bone or the curved edges of shells into a roughly hook-like form. Perhaps people carved wooden ones even earlier, but these would not have been preserved. Some time later a thoughtful individual may have imagined that a barb behind the hook’s point might make it less likely to slip out of a fish’s mouth. This and other advances must have been greatly aided by improvements in the working of metals. The historical details are likely to remain obscure, but barbed metal fishhooks were in use about twenty thousand years ago.

Things obviously did not stop there. Fishhooks today come in a great variety of shapes and sizes. Some have more than one barb or more than one point, often three turned 120° from one another. They vary in size, from those designed to take large sharks to those used in fly fishing for miniature trout. They vary in materials used and in the length of the shank, the curvature of the hook, and the placement of barbs. These variations did not all arise in final form from some contriver’s inspiration. Fishermen using the hooks noted, from long experience, that some variants worked better than others for different fish and different circumstances. The evolution of fishhooks has undoubtedly been much influenced by a selection process. Those variants found to catch more fish were more likely to be made (or ordered) than those that caught fewer—a process that takes place with or without understanding. If a hook with a 20-millimeter shank was more reliable than one with a 25-millimeter shank, it would be favorably selected. There was no need to understand why 20 was better than 25.