Creatures of Accident addresses the most important question in evolutionary theory: How do complex creatures arise from simple ones? This "vertical" dimension of evolution has been downplayed in the literature with unsavory political views. The avoidance of evolution's vertical dimension has, however, left evolutionary biology open to the perception, from outside, that it deals merely with the diversification of rather similar creatures, all at the same level of "advancedness" from a common ancestor-as, for example, in the classic case study of Darwin's finches, with their different beaks.

Wallace Arthur is a professor of zoology at the National University of Ireland,
Galway. The author of seven previous books, he also serves as European editor of the journal Evolution and Development.

Preface	p. ix
Hand Luggage Only	p. 3
The Biased Buddhist	p. 15
Sandcastles and Their Children	p. 21
A Deafening Silence	p. 40
Cork Prisons	p. 55
Building a Castle of Cells	p. 67
Dances with Genes	p. 79
Life Through Time	p. 89
The Embryo Wars	p. 101
Darwin and His Legacy	p. 114
Possible Creatures, Probable Creatures	p. 126
Duplicate and Diversify	p. 136
The Best Box of All	p. 150
From Simple to Complex	p. 161
From Complex to Even More Complex	p. 112
Acquiring Your Head	p. 183
Crossing the Threshold	p. 194
Dinosaur Blues	p. 205
Beyond Pluto	p. 216
Big Questions	p. 225
Glossary	p. 233
Further Reading	p. 241
Acknowledgments	p. 243
Index	p. 245
Table of Contents provided by Ingram. All Rights Reserved.

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Chapter One
HAND LUGGAGE ONLY

Human thinking about the nature of life has been constrained by dogmatic ideological stances, not just religious and political ones, but also adherence to the scientific orthodoxy of the day. Such “philosophical baggage” needs to be jettisoned at the outset of our journey so that we open our minds to the maximum range of possibilities. Science should be all about open-mindedness and questioning. It is an honest search for the truth about the nature of “life, the universe and everything,” to use that famous phrase introduced by Douglas Adams in his book The Hitchhiker’s Guide to the Galaxy.

This book, like the animal kingdom, had an accidental origin. The seed from which it eventually germinated was sown by a newspaper article I read a few years ago. The retention of this seed of information for several years is a bit odd, because newspapers, unlike books, are ephemeral things. If you have already read today’s paper, how many articles can you remember? What about yesterday’s? Or last week’s? We pass our time on trains and planes perusing the papers, but we don’t commit much to memory—or at least to the long-term version of that everyday miracle.

However, occasionally something sticks. The article whose message stuck with me was in the color supplement of one of the Sunday papers. It was about evolution. A particular sentence is all that I retain, and doubtless in imperfect form. But, to an approximation, here it is: “Complex creatures, like humans, are a mere epiphenomenon in the history of Life.”

What did its author mean by describing us as an “epiphenomenon,” that is, a sort of blip on the periphery of something altogether more important? What was the deep philosophical point he was trying to impart? Well, his point was something like this. Since life began about four billion years ago, the vast majority of the creatures that have lived out their lives in every corner of our planetary home have been bacteria. This in itself is hardly surprising, because bacteria are very small, and small creatures tend to be much more numerous than large ones. You and I are both individual humans, but we are also both roving vehicles transporting millions of bacteria from place to place—most of them in our guts and on our skin.

But the point goes further. Not only are there far more bacteria than animals or plants; there are also more different types of bacteria. In other words, species. We all recognize different species of animals, whether very different, like humans and houseflies, or only slightly different, like horses and donkeys. In contrast, different species of bacteria require more than the naked eye to see, let alone distinguish. Indeed, the whole concept of a species—bounded by its members’ inability to breed with other than same-species partners—is hard to apply in the bacterial realm, where reproduction is hardly sex as we know it.

Such difficulties aside, it is probably true that both now and at all other points in evolutionary time the living world has been dominated by bacteria, both in numbers of individual creatures and in numbers of types of creatures. This fact is at odds with a curious human practice—naming particular periods of the earth’s history after a particular kind of animal, as in the Age of Fishes. Such names have a rationale but also serve to mislead. They are normally used to refer to a type of animal that diversified rapidly in the period concerned and consequently contributed much to its fossil record. But unlike fish, most bacteria have no hard parts and rarely fossilize. So fossil frequencies are a poor guide to the dominant creatures of the past. In reality, the whole of evolutionary time could be labeled the Age of Bacteria.

Under this view of life, we humans and our animal allies are indeed a “mere epiphenomenon,” or, in more graphic terms, a tiny molehill on a vast bacterial lawn. A molehill that may one day disappear, whether by self-inflicted nuclear radiation or other means, leaving our simpler but more robust progenitors to go about their bacterial business in a molehill-free manner, as they were doing three billion years ago.

I’m going to call this lawn-with-molehills perspective the left-wing view of life. The reason for this label is that, in this perspective, attention is focused on diversity—that is, creatures being merely different from each other within a level of complexity—rather than on complexity, and on evolutionary increases in this over time. There is a reluctance to think of any local corner of this variety as being better or higher in some sense than another. So it is an egalitarian view of life. We life-forms are all comrades in our struggle for existence, whether we are bacteria, beetles, blue whales, or bus drivers.

So what is the right-wing view? This is where we go from lawn to ladder. A long time ago in Germany—about two centuries back—a group of philosophically minded folk interested in the nature of life came up with the idea that all creatures could be arranged in a line. And the line was a vertical one: it was effectively a sequence of increasing complexity and sophistication. Microbes at the bottom, humans at the top. This is something of a caricature, but it captures these philosophers’ fundamental point.

This vertical line needs a name. It is often referred to by the Latin scala naturae, meaning, as you might expect, “natural scale.” Whatever we call it, any overall view of life based on it is fundamentally at odds with the lawn-with-molehills view. If our central metaphor shifts from horizontal to vertical, we change our focus from diversity to complexity. From humans as molehill to pinnacle. From bacteria as all-dominant life-forms to lowly dwellers on the bottom rung.

Now, each of these views captures an element of truth. It is always unwise to regard thinkers of the past as ignorant or deluded. The further back we go, the less the information at the disposal of the thinkers concerned. But while lack of some kinds of information constrains thinking, it does not necessarily distort it. That is, it does not prevent a rigorous analysis of whatever information was available at the time. So I am not interested in being critical of last decade’s Sunday newspapers or of worthy tomes written in the eighteenth and nineteenth centuries in a language that regrettably I cannot read. Sure, my criticism is implicit, but I will not develop it. Instead, what I will develop is a Middle Way, to borrow that famous Buddhist concept, between the left-wing and the right-wing views—that is, between life’s lawn and life’s ladder. However, it will be a decidedly biased Middle Way—more on that in the following chapter.

Today, the worldview of most Europeans, and many (but not most?) Americans, is sufficiently infused with evolutionary thinking that the idea of evolution in general causes an adverse response only in the creationist movement. There are now many strands of this movement, the most recent being intelligent design, or ID.

If all that phrase implied were an intelligent Creator causing the big bang through which the universe was born some fourteen billion years ago and then standing back to let nature run its course, it would seem no great threat to an evolutionary worldview. But unfortunately it goes further. I will return to this point toward the end of the book (in Chapter 20). Most of the book is not devoted to attacking ID, but rather to building the case that ID is unnecessary by explaining, in a way that is readily accessible to a general readership, how the rise of complex creatures can be explained in terms of natural processes. I will take the view that we should all accept evolution regardless of whether we do or do not see religious implications, because of the mass of accumulated evidence in its favor, some of which we will see in subsequent chapters. But accepting evolution was not so easy in the late eighteenth century.

We need to be careful here. What exactly was the state of human thinking 220 years ago? How uniform or varied were people’s views of life? It is easy to make ill-informed statements about such times that historians of science could disprove in a single sweep of the pen. Belief in evolution did not begin with Charles Darwin and his 1859 masterpiece, On the Origin of Species. That book may indeed have been the biggest single milestone along the way from a dominance of creationist myths to the triumph of evolutionary arguments, but it was not the first. European views on evolution can be traced back at least half a century earlier, and probably further. And who knows what the Chinese were thinking about life way back centuries before Darwin’s time, when they scooped Copernicus with their early ideas on a heliocentric solar system?

But caution should not go too far. Although you and I have little insight into the philosophical conversations that took place in late-eighteenth-century Germany, we can be fairly sure that evolution was not center stage at that time. I’d guess that some folk had thought of it. Regardless of whether this is true, evolution still did not feature in the prevailing European worldview by 1800.

This fact raises an interesting question. What was in the minds of those late-eighteenth-century proponents of the right-wing view? If life had a ladder, did creatures not climb up it? No, they emphatically did not. The ladder, which now so readily permits an evolutionary interpretation, was at the time very abstract—a pattern in the mind of God.

Now, in post-Darwinian times, creatures most certainly are seen to climb the ladder—but only some of them. Many creatures have remained on the lawn of design simplicity ever since life began. That is, they have remained as single cells. Others have climbed ladders that led to greater complexity, in some cases to designs that involved many millions of cells. Exactly how they climbed the ladders we’ll get to later, and clearly Darwinian natural selection is a part—though only that—of the answer. For now, the main thing to notice is that the ladder has been pluralized. There has not been a single escape route from the realm of the simple; rather, there have been several. Some led to greater heights than others. After all, even some bacteria have climbed a short ladder to what are called filamentous designs. These involve cells sticking together in strings rather than all existing as entirely independent creatures. And plants climbed a very different ladder from animals.

It gets worse. Evolution is more like the child’s board game Snakes and Ladders than it is like ladders alone. Once you have ascended far enough, it is possible to go down as well as up. As one line of ancestors and descendants (a lineage) is going up, another is going down. Now we get into a terminological and pictorial morass. Darwin called one of his books The Descent of Man. More recently, the Polish-British-American scientist Jacob Bronowski wrote a book, and presented a TV series, called The Ascent of Man. In biological texts, evolutionary trees are usually pictured as going up; but occasionally they are shown as going down, or even sideways. Human family trees, and diagrams of genetic crosses, are usually shown as going down, though they are mere microcosms of those bigger evolutionary trees that usually go up.

The morass in which we now find ourselves is sometimes referred to as philosophical baggage. Every individual thinker carries into every stage of his or her thinking a set of views (good) or prejudices (bad) that have been born of previous reading, thinking, and talking. We are by nature reflective creatures, albeit some more so than others, and we cannot help forming pictures of the world as we learn about it. But these pictures, although they are essential tools in the learning process, can lodge too firmly in our minds at too early a stage and inhibit shifts to different pictures that may become appropriate as we learn more. And this problem characterizes the whole human learning endeavor at the community level as much as it does our own individual mental journeys through life. We must be eternally vigilant about the need to discard our philosophical baggage when it becomes a hindrance rather than a help. Nobody should underestimate the difficulty that lies in maintaining this constant vigil, and in using it to good effect.

A particular kind of philosophical baggage lies at the heart of the morass of ascent and descent metaphors that we have just reached. This baggage concerns our particularly human identity crisis: our views, which tend to be strongly held because they matter so much to us, about what kind of creatures we are, how we got here, where we are going, and whether there is any ultimate purpose in our journey, save that which we make up ourselves as we travel.

This is the worst kind of baggage because it is the most important and thus the most difficult to discard. But discard it we must, even if only temporarily, in order to reach an unprejudiced view of the nature of life, a view based on facts rather than on ideology. The first step in discarding it is to inspect it carefully so that we can see its full extent. You can’t discard baggage that you don’t know you’re carrying.

So back to the left-wing and right-wing views of life, or the lawn and the ladder. This time I’ll take them in the opposite order, which is the order in which they historically arose.

The right-wing view emphasizes differences rather than similarities. Moreover, it emphasizes a single dimension along which (or, more accurately, up and down which) the differences among creatures are manifest. But what is this dimension? I referred to it earlier as being complexity or sophistication. Other terms could be, and have been, used. Some creatures can be described as of a higher grade or as being more advanced than their lower or more primitive relations. It is probably reasonable to describe humans as being more advanced in some sense than flies. Is it equally reasonable to describe flies as being more advanced than snails? Probably not—they’re just different. What if we replace snails with their brighter molluskan cousin the octopus? Most people would describe the octopus as more advanced than the fly, largely because of the octopus’s greater capacity for learning.

Notice, however, that learning is not the same as complexity, though they are related. It is probably true to say that no very simple animal has a large capacity for learned, as opposed to instinctive, behavior. There are no brainy flatworms. But there certainly are many animals that are structurally complex yet limited in the realm of learning. This is true, for example, of sea urchins and centipedes.

…

Excerpted from Creatures of Accident : The Rise of the Animal Kingdom by Wallace Arthur. Copyright © 2006 by Wallace Arthur. Published in September 2006 by Hill and Wang, a division of Farrar, Straus and Giroux, LLC. All rights reserved.

Excerpted from Creatures of Accident: The Rise of the Animal Kingdom by Wallace Arthur
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