The title of this book, Origins of Order: Self-Organization and Selection in Evolution, states the book's task: To answer the question, What are the sources of the overwhelming and beautiful order which graces the living world? To presume to ask such a question is also to know one must not presume to succeed. Questions such as this must ever be asked anew as each generation comes to perceive new ways of ordering its view of life.

One view, Darwin's, captives us all: natural selection and the great branching tree of life, spreading from the major phyla to the minor genera and species, to terminal twigs, to curious humans seeking their place. Darwin and evolutionism stand astride us, whatever the mutterings of creation scientists. But is the view right? Better, is it adequate? I believe it is not. It is not that Darwin is wrong, but that he got hold of only part of the truth. For Darwin's answer to the sources of the order we see all around us in overwhelmingly an appear to a single singular force: Natural selection. It is this single-force view which I believe to be inadequate, for it fails to notice, fails to stress, fails to incorporate the possibility that simple and complex systems exhibit order spontaneously. That spontaneous order exists, however, is hardly mysterious. The nonbiological world is replete with examples, and no one would doubt that similar sources of order are available to living things. What is mysterious is the extent of such spontaneous order in life and how such self-ordering may mingle with Darwin's mechanism of evolution---natural selection---to permit or, better, to produce what we see.

Biologists have not entirely ignored the spontaneous emergence of order, the occurrence of self-organization. We all know that oil droplets in water manage to be spherical without the benefit of natural selection and that snowflakes assume their evanescent sixfold symmetry for spare physiochemical reasons. But the sheer imponderable complexity of organisms overwhelms us as surely as it did Darwin in his time. We customarily turn to natural selection to render sensible the order we see, but I think the answer to our questions about the origins or order is broader. We already have some inkling of the kinds of spontaneous order which may bear on biological evolution, and I believe we must make the most profound assessment of such self-organization. We must look in any direction that seems profitable because whatever spontaneous may abound is available for evolution's continuing uses.

What makes the present stage of biological science so extraordinary is that molecular biology is driving us to the innermost reaches of the cell's ultimate mechanisms, complexity, and capacity to evolve. At the very same time, work in mathematics, physics, chemistry, and biology is revealing how far- reaching the powers of self-organization can be. These advances hold implications for the origin of life itself and for the origins of order in the ontogeny of each organism. One major theme of this book is an effort to link recent work in molecular biology with these new insights into spontaneous order in complex systems. Union of the two streams of insight promises to transform our understanding. The order inherent in the busy complexity within the cell may be largely self-organized and spontaneous rather than the consequence of natural selection alone.

Yet our task is not only to explore the sources or order which may lie available to evolution. We must also integrate such knowledge with the basic insight offered by Darwin. Natural selection, whatever our doubts in detailed cases, is surely a preeminent force in evolution. Therefore, to combine the themes of self-organization and selection, we must expand evolutionary theory so that it stands on a broader foundation and then raise a new edifice. That edifice has at least three tiers:

We must delineate the spontaneous sources of order, the self- organized properties of simple and complex systems which provide the inherent order evolution has to work with ab initio and always.

We must understand how such self-ordered properties permit, enable, and limit the efficacy of natural selection. We must see organisms in a new light, as the balance found, the collaboration achieved, when natural selection acts to further mold order which preexists. In short, we must integrate the fact that selection is not the sole source of order in organisms.

We must understand which properties of complex living systems confer on the systems their capacities to adapt. For Darwin simply assumed that the accumulation of advantageous mutations was possible, and yet the capacity to do so is not self-evident. Some systems can hardly adapt at all. Indeed, we must investigate the possibility that selection itself achieves the kinds of organisms which can adapt successfully. Therefore, we must also wonder whether there may be characteristic features so deeply requisite for the capacity to adapt in a coevolutionary process that their presence in organisms is itself a lawlike consequence of selection operating on complex coevolving systems.

While these points hardly seem contentious, it is no secret that we have, as yet, no theory which embodies them. Physics has its examples of remarkable order, but no use for natural selection. Biologists are secretly aware that selection must be working on systems which to one degree or another exhibit order by themselves. D'Arcy Thompson (1942) told us so with eloquence years ago, but we have not troubled to think through the implications. How strange, yet therefore how inviting, that we may one day bring ourselves to see life in a new light.

The major parts of the book discuss the following topics.

The introduction, Chapter 1, outlines our contemporary view of organisms, order, and evolution. Here we have been persuaded by Monod's (1971) evocative phrase, "Evolution is chance caught on the wing." And we are equally persuaded by Jacob's (1983) view that evolution "tinkers together contraptions." Here broods our sense of organisms as ultimately accidental and evolution as an essentially historical science. In this view, the order in organisms results from selection sifting unexpected useful accidents and marshaling them into improbable forms. In this view, the great universals of biology---the genetic code, the structure of metabolism, and others---are to be seen as frozen accidents, present in all organisms only by virtue of shared descent. The quiet sense that spontaneous order is everywhere present is itself not central to this view. Hence it is not stressed, not investigated, not integrated.

The first part of the book, Chapters 2 through 6, examines the power and limits of selection when acting on complex systems exhibiting spontaneous order, explores our first examples of self-organization, and proposes that the evolutionary marriage of self-organization and selection is itself governed by law: Selection achieves and maintains complex systems poised on the boundary, or edge, between order and chaos. These systems are best able to coordinate complex tasks and evolve in a complex environment. The typical, or generic, properties of such poised systems emerge as potential ahistorical universals in biology.

None can doubt Darwin's main idea. If we are to consider the implications of spontaneous order, we must certainly do so in the context of natural selection, since biology without it is unthinkable. Therefore, we must understand how selection interacts with systems which have their own spontaneously ordered properties. At a minimum, we must wonder whether selection in sufficiently powerful to obviate any inherent order in life's building blocks. If so, the order seen might reflect selection's dictates alone. Thus Chapters 2 to 4 consider the character of adaptive evolution under strong natural selection on mountainous "fitness landscapes," with high mountain tops representing peaks of fitness and ridges and deep valleys representing low fitness. We shall in fact find critical limits to me power of selection: As the entities under selection become progressively more complex, selection becomes less able to avoid the typical features of those systems. Consequently, should such complex systems exhibit spontaneous order, that order can shine through not because of selection, but despite it. Some of the order in organisms may reflect not selection's success, but its future.

Much of the discussion in Chapters 2 to 4 focuses on adaptation in sequence spaces, such as among possible DNA or protein sequences, where we can conceive of evolution as carrying out adaptive walks toward peaks that represent how well proteins perform specific catalytic or ligand binding tasks. Consideration of the evolution of proteins able to carry out new catalytic functions, in turn, leads to the abstract concept of a catalytic task space. Among the implications of such a space is that about 100 million roughed-in enzymes might constitute a universal enzymatic toolbox able to catalyze almost any reaction. The immune repertoire of about 100 million may already be a first example of such a universal set. This possibility is not merely abstract, for Chapter 4 leads us toward practical implications as well. It is now possible to use genetic-engineering techniques to generate extremely large number of random or quasi-random DNA sequences, hence very large numbers of random or quasi-random RNA sequences and quasi-random proteins. Thus it is possible to explore sequence spaces for the first time. I believe this exploration will lead in the coming decades to what might be called "Applied Molecular Evolution" with very great medical and industrial implications, such as rapid evolution of new drugs, vaccines, biosensors, and catalysts.

Chapter 5 seeks the principles of construction in "parallel-processing" integrated systems of elements that allow the systems to adapt their behavior in a complex environment. We find two themes: First, the emergence of profound spontaneous order. Second, a bold hypothesis that the target of selection is a characteristic type of adaptive system poised between order and chaos. The unexpected spontaneous order is this: Vast interlinked networks of elements behave in three broad regimes---ordered, chaotic, and complex regime on the frontier between order and chaos. The spontaneous order of the ordered regime foretells much of the order seen in aspects of developmental biology. The bold hypothesis states construction requirements which permit complex systems to adapt optimally through accumulation of useful mutations, even in a coevolutionary context where an adaptive move by one "player" distorts the fitnesses and the fitness landscapes of the coevolving partners. Ordered systems, particularly those near the edge of chaos, have the needed properties.

In Chapter 6, we see that the same construction requirements find echos at higher levels, such as whole ecosystems. Here the problem is to understand how such systems are coupled so that members coevolve successfully and how selection itself may achieve such coupling. Again, such ecosystems can behave in three broad regimes---ordered, complex, and chaotic. Again, remarkably, coevolving systems may optimize their capacity to coevolve by mutually attaining the edge of chaos.

The second and third parts of the book discuss other major examples of powerful self-ordering. In each case, the spontaneous order appears so impressive that it would be shortsighted to ignore the possibility that much of the order we see in the biological world reflects inherent order.

In the second part, Chapters 7 to 10, I discuss the origin of life. It requires no more words than this phrase to remember that we do not now know how life may have started. Any discussion is at best a body of ideas. The central problem is this: How hard is it to obtain a self-reproducing system of complex organic molecules, capable of a metabolism coordinating the flow of small molecules and energy needed for reproduction and capable of further evolution? Contrary to all our expectations, the answer, I think, is that it may be surprisingly easy. To state it another way, I want to suggest that we can think of the origin of life as an expected emergent collective property of the modestly complex mixture of catalytic polymers, such as proteins or catalytic RNA, which catalyze one another's formation. I believe that the origin of life was not an enormously improbable event, but law-like and governed by new principles of self-organization in complex webs of catalysts. Such a view has many implications. Among them, the template- replicating properties of DNA and RNA are not essential to life itself (although these properties are now essential to our life). The fundamental order lies deeper, the routes to life are broader.

Further, I suspect that the same principles of self-organization apply to the emergence of a protometabolism. I suggest that the formation of a connected web of metabolic transformations arises almost inevitably in a sufficiently complex system of organicmolecules and polymer catalysts. This view implies that, from the outset, life possessed a certain inalienable holism. It also suggests that almost any metabolic web, were life to evolve again, would have a very similar statistical structure. Thus I find myself wondering if the web structure of a metabolism may reflect not the contingent consequences of this particular history of life, but some underlying ordering principles in biology.

These ideas are generalized in Chapter 10 to a new class of "random grammar" models which exhibit functional integration and transformation in coevolving systems, ranging from prebiotic chemical systems with protoorganisms to the emergence of mutualism and antagonism between simple organisms to similar features of economic and cultural systems. Grammar models are new testbeds for the locus of law in deeply historical sciences such as biology.

The third part, Chapters 11 to 14, examines the "genetic program" which controls cell differentiation during development of the adult from the fertilized ovum, and the machinery which yields ordered morphologies. The main intent is to suggest that many highly ordered features of ontogeny are not the hard-won achievements of selection, but largely the expected self- organized behaviors of these complex genetic regulatory systems.

The problem of cell differentiation, the focus of Chapters 11 to 13, is one of the two most basic issues in developmental biology. Different cell types---nerve, muscle, liver parenchymal---arise and differentiate from earlier cell types during development and, ultimately, in a human, form several hundred cell types. Each cell in a human's body contains essentially the same genetic instructions as all other cells. Those instructions include the structural genes coding for aobut 100 000 different proteins. Cell types differ because different subsets of genes are "active" in the different cell types. The activation and repression of genes is itself controlled by an elaborate regulatory network in which the products of some genes switch other genes on or off. More generally, expression of gene activity is controlled at a variety of levels, ranging from the gene itself to the ultimate protein product. It is this web of regulatory circuitry which orchestrates the genetic system into coherent order. That circuitry may comprise thousands of molecularly distinct interconnections. In evolution, the very circuitry is persistently "scrambled" by various kinds of mutations, as is the "logic" of the resulting developmental program.

In Chatpers 11 to 13, I try to show that such properties as the existence of distinct cell types, the homeostatic stability of cell types, the number of cell types in an organism, the similarity in gene expression patterns in different cell types, the fact that development from the fertilized egg is organized around branching pathways of cell differentiation, and many other aspects of differentiation are all consequences of properties of self- organization so profoundly immanent in complex regulatory networks that selection cannot avoid that order. All aspects of differentiation appear to be properties of complex parallel-processing systems lying in the ordered regime. These properties may therefore reflect quasi-universal features of organisms due not to selection alone, but also to the spontaneous order of the systems on which selection has been privileged to act.

Chapter 14 treads D'Arcy Thompson's ground and considers the second fundamental problem in developmental biology: morphology. The actual morphologies of organisms must also be viewed as a collaboration between the self-ordered properties of physicochemical systems together with the action of selection. Oil droplets are spherical in water because that is the lowest energy state. The membrane of a cell, a bilipid structure, forms spherical closed surfaces because that is its lowest energy state. Other aspects of spatial order in organisms reflect dissipative structures rather like whirlpools, which require a continuous flow of matter and energy to maintain the form. Thus the genome's capacity to generate a form must depend on very many physicochemical processes constituting a panoply of developmental mechanisms beyond the sheer capacity of the genome to coordinate the synthesis of specific RNA and protein molecules in time and space. Morphology is a marriage of underlying laws of form and the agency of selection. The task is to find the laws and hallow the marriage.

I should make it clear that there are many fundamental problems in evolution and development which I have made no attempt to discuss. Most notably, the study of evolution has focused and will continue to focus on analysis of branching phylogenies, with related debates about the tempo and mode of evolution and the roles of natural selection and drift in the evolutionary process. In the best sense, this tradition studies this history of life. My aim in this book, nowhere in opposition to the familiar tradition, is to examine some new directions in which the occurrence of spontaneous order underpins this history of life.

I should also stress that, while the book is finished, it is not a finished book. Some of the subjects are familiar and can be discussed with a modest sense of completion. Others, however, constitute new areas of thought and investigation. Premises and conclusions stand open to criticism. If usual, I hope they are open to improvement.