Randomness in Evolution
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About this ebook
The important role that randomness plays in evolutionary change
John Tyler Bonner, one of our most distinguished and insightful biologists, here challenges a central tenet of evolutionary biology. In this concise, elegantly written book, he makes the bold and provocative claim that some biological diversity may be explained by something other than natural selection.
With his customary wit and accessible style, Bonner makes an argument for the underappreciated role that randomness—or chance—plays in evolution. Due to the tremendous and enduring influence of Darwin's natural selection, the importance of randomness has been to some extent overshadowed. Bonner shows how the effects of randomness differ for organisms of different sizes, and how the smaller an organism is, the more likely it is that morphological differences will be random and selection may not be involved to any degree. He traces the increase in size and complexity of organisms over geological time, and looks at the varying significance of randomness at different size levels, from microorganisms to large mammals. Bonner also discusses how sexual cycles vary depending on size and complexity, and how the trend away from randomness in higher forms has even been reversed in some social organisms.
Certain to provoke lively discussion, Randomness in Evolution is a book that may fundamentally change our understanding of evolution and the history of life.
John Tyler Bonner
John Tyler Bonner is professor emeritus of ecology and evolutionary biology at Princeton University. His books include The Social Amoebae: The Biology of Cellular Slime Molds and Why Size Matters: From Bacteria to Blue Whales (both Princeton).
Read more from John Tyler Bonner
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Reviews for Randomness in Evolution
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- Rating: 4 out of 5 stars4/5Bonner's argument in this long essay is essentially, the simpler the organism, the less role natural selection plays in evolution - randomness plays a much larger role. This is a very short essay on a topic sure to cause much debate in his field. I am not a biologist, but I believe Bonner has made a persuasive argument and look forward to the discoveries which will be made by those testing his thesis.
Book preview
Randomness in Evolution - John Tyler Bonner
essay.
PREFACE
Many biologists, and I am one of them, live two lives at the same time. In one they work with organisms from day to day in the laboratory, or in the field. This is what keeps them in touch with their subjects—the real world that they find so fascinating. The other life is a concern for the big picture: how it all fits together. No one gives a better example of this double life than Charles Darwin, with his long and excruciatingly detailed study of barnacles, on the one hand, and his breathtaking excursion into evolution, on the other. From a biologist’s point of view there can be no bigger picture than the latter.
In my case the microscopic cellular slime molds have been my barnacles, and my mini journeys into looking at the broader picture have been put forth in essays over the years. Often they have been concerned with bringing forth a hidden phenomenon, or showing connections between different realms of biology that are much more closely related than convention would have it. I have been led to seek the big picture, one that ties together facts and ideas that are generally thought of as entirely separate. For instance, years ago I was concerned that the study of the development of organisms was limited to very few organisms, such as sea urchins and amphibians, yet the variety of organisms that develop is great. I felt that comparative studies of development would be essential for generating new insights into the venerable study of embryology and its relation to evolution. Later I was struck by the similarities between cell societies that make up a multicellular organism and animal societies, such as those of ants and other insects and mammalian societies as found in various species of monkey: the same forces make them tick. Then I became intrigued by the ways the essential communication between cells during development fell in neatly with the then new discoveries of that time of Nikolaas Tinbergen and Konrad Lorenz in the rising field of ethology; it was a different way of looking at the evolution of development.
My big picture
kept changing. I soon realized the great importance of the concept of life cycles, and this led me to appreciate the importance of size. Life cycles of a multicellular organism (such as ourselves) start off as a minute fertilized egg and keeps getting larger and larger until maturity. This is as true for a small alga as it is for a blue whale. Furthermore, if one looks at the history of our planet, it is evident that the maximum size of animals and plants progressively increases over geologic time (a matter to be pursued further in the pages that follow). This size increase is fundamentally tied with an increase in complexity—what I have called the size-complexity rule.
And all during this series of generalizations that I have indulged in over the years, I have kept my eye firmly fixed on the cellular slime molds, my barnacles.
This book is a continuation of my quest for the big picture. I work with microorganisms and I ask the question: Are they affected by natural selection the same way as large, complex ones? It is conventional to think that selection acts the same way on organisms of all sizes, and I make the case that it might not be so. I was delighted to find that in a brief passage, Darwin also suggested the same idea in one of the later editions of his On the Origin of Species.
Margaree Harbour
Cape Breton, Nova Scotia
RANDOMNESS IN EVOLUTION
CHAPTER 1
Life and the Riddle of Randomness
As biologists our great aim is to find order in all the diversity and complexity of the living world. This is something we all strive for: it is what gives us a feeling of fulfillment and satisfaction. We seek the rules that underlie living phenomena to make ignorance and confusion turn into clarity and order. This is what Linnaeus did by finding a way to classify the vast numbers of different kinds of animals and plants: he brought order out of chaos. And this is what Mendel did with crossing his peas to reveal the basic rules of inheritance, a discovery of such great importance that it provided the basis for the majority of the advances in biology—which have been profound—in the twentieth, and now into the twenty-first century.
The great advance of Charles Darwin in discovering natural selection was another momentous step forward. It explained how organisms could evolve, how they, through successive generations, could become optimally adapted to their environment. There is continual competition between individuals, and the winners are the ones that are successful in producing offspring, thereby passing on the advantageous traits. All biologists today are so in harmony with this idea that it frames all our thoughts, so much so that it has a way of obscuring for us some important and peripheral factors that seem to be less worthy of our attention. But I think they are important, and this book is an attempt to put one of those factors before our eyes.
The most obvious one is randomness. There is something about this idea that is unsettling to many, no doubt because it goes directly against the more comfortable feeling of the order that we all seek. For this reason there is less written on randomness in evolution than on selection, although it is by no means totally absent, as we shall see. Compared to natural selection, it is no great enlightening principle, and therefore it is often relegated to a background noise that really is not doing anything. Natural selection carves out novelties that lead to evolution: randomness seems to go nowhere; it just shuffles things backwards and forwards. While there is some truth to this way of putting the matter, it is fundamentally wrong, as I plan to show in some detail. All of evolutionary change is built on a foundation of randomness. It provides the necessary material for natural selection which then does indeed bring forth the order our inner mind so actively craves.
More than that, we will see examples where randomness is literally put to use as a way of managing a key step in development of an organism (and also in animal societies). In evolution randomness can, in some special circumstances, directly produce order.
The part that randomness plays in evolution differs with the size of the organism. In fact, this is what alerted me to the subject. For many years I have worked with small cellular slime molds, and because of them I have been much concerned in the matter of how size influences both the development and the evolution of organisms. As I bore into this interesting matter I realized that most evolutionary biologists, following the tradition of Darwin, think in terms of large or at least complex plants or animals, and assume that microorganisms are no different despite their small size. There are those who work on the evolution of bacteria and often can distinguish between their characteristics and those of larger eukaryotic organisms, but the prokaryotic world is in some ways a specialized subject, although one of great interest.
An important point should be made right in the beginning. In this book I will be concerned with the variations in morphology. Bacteria, and other prokaryotes, have a very limited morphological variation, and therefore my argument here only concerns eukaryotes, whose cells contain a nucleus and come in a great variety of shapes. Those vast numbers of varieties involve both unicellular and multicellular forms.
Chance in Evolution
The role of chance in evolution has a venerable history, and there has been a recent renewed interest. It was recognized early in the history of genetics that mutations were random. More recently, and for many years, this randomness was understood at the molecular level where one of the bases in a DNA chain substituted for another. There have been many attempts to show that in some circumstances mutation might force change in a particular direction, but these experiments have not stood up with time; the idea that mutations are random has long been generally accepted. It should be noted that this fact has been used by skeptics to doubt Darwin and his natural selection: how can the complexity and the beauty of a bird or a flower be explained by a mechanism rooted in the chaos of randomness! But indeed it can, and we have more and more evidence that there are numerous aspects of evolution besides mutations that involve chance. There is