Although bacteria are still all around us as well as inside us (it is estimated that there are more bacteria in us than the number of our own cells, of which there are at least a trillion and maybe many more), let us return to the only slightly more complex organisms of which we are ultimately composed: the eukaryotes. It is true that bacteria can form colonies, referred to as biofilms, or, more colloquially, as slime, and that in their collective state they differ somewhat in their cellular structure from their state as independent organisms, but it is from eukaryotes that most multicellular bodies, including all the more complex ones, derive. Eukaryotes are on average 100 to 1,000 times larger than bacteria, so that the largest of them may be just visible to the naked eye. They represent a significant increase not only in size but in complexity compared to prokaryotes: they have an internal nucleus that contains the DNA and that is the result of some kind of cell symbiosis. Given the firm exterior surface of the prokaryotes, combining them in a new form was no mean feat. It took perhaps a half billion years for life to emerge from the seas of the early earth, but it took another 1.5 billion before the eukaryotes emerged.
Remembering Gould’s strictures about the predominance of prokaryotes and eukaryotes, and the fact that multicellular organisms formed of differentiated eukaryotic cells are mere twigs on the bush of life, we may still consider the remarkable path that these twigs would take and the fact that one of them would eventually lead to us. John Maynard Smith and Eors Szathmary, in their book The Major Transitions in Evolution, describe the developments of unicellular organisms that we have noted above; the appearance of sexual reproduction among the eukaryotes; the appearance of multicellular eukaryotic organisms involving the differentiation of cells and leading to the three major divisions of fungi, plants, and animals; the development of colonies of multicellular organisms involving nonreproductive castes among some insect groups; the development of primate and then human societies; and finally the development of language among humans.32 Smith and Szathmary account for all of these transitions in terms of classical Darwinian natural selection.
Conserved Core Processes
Marc Kirschner and John Gerhart, in their book The Plausibility of Life, develop a conception of the organismic control of variation that does not deny but does extend the classical view of natural selection.33 Because their focus is on animals, they will move us closer to human evolution as the background for understanding religion. Fungi and plants are enormously successful forms of multicellular life of great interest in themselves, but not essential for purposes of my story. In my attempt to translate Kirschner and Gerhart’s very complex argument for the purposes of this book, I will inevitably oversimplify, so I warn the reader to consult this important book rather than rely on my summary.
The key to Kirschner and Gerhart’s argument is the idea of facilitated variation, which involves much more selective activity by the organism than the usual notion of random mutation suggests. But facilitated variation makes sense only in terms of their other key concept: conserved core processes. What Kirschner and Gerhart stress is that mutations can occur only in organisms that are already structures-already have core processes that have persisted through long ages of evolutionary history-and that mutations, though inevitably random, will be accepted or rejected in terms of how they relate to the conserved core processes. The primary contribution of the book is to clarify how conserved core processes promote variation, that is, “facilitated variation,” in ways that produce novel developments in phenotypes without undermining the continuity of the core processes. Stability and change, in this view, enhance each other rather than conflict with each other.
Although the book’s main contribution is its spelling out of facilitated variation at the level of cell biology, its argument depends on the notion of conserved core processes, whose origin they do not claim to have fully explained. All of life is a development of the first core process, that of the prokaryote cell. “The most obscure origination of a core process is the creation of the first prokaryotic cell. The novelty and complexity of the cell is so far beyond anything inanimate in the world of today that we are left baffled by how it was achieved..“3’ But as with all core processes, the emergence of the prokaryotes produced consequences that are still at work in all living organisms:
The chemistry of the processes was evolved at least three billion years ago; the components and their activities have been retained unchanged to this day, transmitted to all offspring of this ancestor. It is an amazing level of conservation. After these millions of millennia of evolution, many metabolic enzymes in the bacterium E. coli are still more than 50 percent identical in their amino acid sequence to the corresponding human enzymes. For example, of 548 metabolic enzymes sampled from E. soli, half are present in all living life forms, whereas only 15 percent are specific to bacteria alone.35
Later core processes share certain characteristics: they occur relatively suddenly, they involve major innovations, and they do not consist of piecemeal accretions but involve whole suites of changes.36 Speaking of the appearance of the second great conserved core process, that of the singlecelled eukaryotes 1.5 to 2 billion years ago, Kirschner and Gerhart write, after describing some of the features of prokaryotes that are reorganized in eukaryotes:
These cases suggest that the great innovations of core processes were not magical moments of creation but periods of extensive modification of both protein structure and function. The changes are not achieved by facilitated variation of the regulatory kind we have described throughout this book. Instead, during great waves of innovation, preexisting components of prokaryotes changed their protein structure and function in fundamental ways to generate the components of new core processes of the eukaryotic cell.37
Kirschner and Gerhart describe “a period of rapid remodeling” that involved “enormous innovations” that are not “magical” but that don’t simply follow the logic of facilitated variation that is central to their book. And again, as with the prokaryotes, the new core processes that emerge from this transition survive with remarkable stability in all subsequent eukaryotes, including the multicellular ones-fungi, plants, and animals, and, of course, us. In describing the suite of features that they speak of as the “invention” (their quotation marks) of eukaryotic cells, they write, “The most striking trait is their size and complexity. They are one hundred to one thousand times larger in volume than bacterial cells and have numerous internal membranes that wall off small compartments or organelles (‘little organs’), which are specialized for different functions.“38
The next “intimation of true novelty” comes from the period of perhaps a billion years ago “when multicellular eukaryotes, including animals, first arose.” Here again we see the appearance of new conserved core processes: “A controlled fluid environment inside the multicellular epithelial organism was a novelty that promoted communication between animal cells via secreted and received signals.” This worked out differently in fungi, plants, and animals, but to speak only of animals, they write, “The controlled internal milieu of animals must have provided the context for the elaboration of a greatly expanded set of signals and receptors, and indeed animals have evolved many kinds of cell-cell signaling.” It is these signaling capacities that lead to the development of differentiated cell types, such as those for blood, muscle, and nerves. “The evolution of differentiated cells was a regulatory accomplishment involving new placements and increased amounts of old components. Once evolved, many of these cell types were conserved in metazoan [animal] evolution, from jelly fish to humans.“39
The next and final set of conserved core processes in Kirschner and Gerhart’s analysis has to do with the emergence of body plans among animals: “By 600 million years ago, fairly complex animals were probably present, branching sponges, radial animals such as jellyfish, and the first small bilateral animals (like us, with mirror-image left and right sides), perhaps rather worm-like in form, which left traces of their burrows in the muddy ocean flo
or, thereafter fossilized. This worm-like animal may have been the ancestor of all modern bilateral animals.” But then:
Rather suddenly, diverse macroscopic anatomy appeared on the Cambrian scene of 543 million years ago. By the Midcambrian, representative animals of all but one of the 30 major modern phyla were present according to fossil records.
The abruptness of the emergence of so many complex anatomies may be an artifact of the special features of fossilization at that time or of some special environmental condition that favored large and more complex animals, or it may be the result of some breakthrough in regulatory control on the cellular level. Once again, a new suite of cellular and multicellular functions emerged rather quickly and was conserved to the present 40
We need not describe the details of animal body plans. Most of them share certain features, such as a mouth at the front and an anus at the rear, some kind of digestive system in between, some kind of heart and circulatory system, at least the beginnings of nerve connections, and so forth. It is worth noting that one phylum that shares features with our own vertebrate phylum, such as heads, often eyes, and so forth, even though some of these features evolved independently, has been notably successful, namely the arthropods. Stephen Gould reminds us, lest we seek to esteem our own class of mammals in the subphylum vertebrata too highly, that “mammals form a small group of some four thousand species, while nearly a million species of multicellular animals have been formally named. Since more than 80 percent of those million are arthropods, and since the great majority of arthropods are insects, [some] enlightened people tend to label modern times as the `age of And the Wikipedia article “Crustaceans” points out that “Crustaceans are among the most successful animals, and are as abundant in the oceans as insects are on land.” So, after the enormously successful unicellular organisms, among the multicellular organisms it is the arthropods who have most successfully radiated in an immense variety of species of significantly higher biomass than mammals.
Of body plans, which have extraordinary longevity and creativity in the production of variation, Kirschner and Gerhart write, “Although the body plan is an anatomical structure, it plays a central role in development, and it too should be called a conserved core process. It joins conserved processes such as metabolism and other biochemical mechanisms, eukaryotic cellular processes, and multicellular processes of development to make up the repertoire of conserved processes of bilateral animals.“42 Summing up, they write:
If we follow the path from the bacterium-like ancestor toward humans, we find repeated episodes of great innovation. New genes and proteins arose in each episode. Afterward, the components and processes settled into prolonged conservation. The existence of “deep conservation” is a surprise. To some biologists it is a contradiction of their expectations about the organism’s capacity to generate random phenotypic variation from random mutation. To some, it borders on paradox when held against the rampant diversification of anatomy and physiology in the evolutionary history of
But it is just Kirschner and Gerhart’s point that random mutation, though essential for the production of variation, never acts through the isolated production of a genetic change. The genes, in fact, in spite of the popular belief reinforced by some science writers, are not little homunculi, “replicators” sitting in their chromosomes and “controlling” the organisms seen as “lumbering robot vehicles.“44 Rather, mutation takes place in phenotypes organized by conserved core processes that are able to produce efficient, and often quite remarkable, change without drastic disruption.
Instead of lumbering robots, organisms are actors in the process of evolution, even in the evolution of evolvability. Kirschner and Gerhart sum up:
On the side of generating phenotypic variation, we believe the organism indeed participates in its own evolution, and does so with a bias related to its long history of variation and selection. Coupled with our already advanced understanding of natural selection and heredity, facilitated variation completes the broad outlines of the general processes of evolution, particularly for metazoan diversity.45
Toward the end of their book, Kirschner and Gerhart raise the question of the generalizability of their analysis beyond biology, recognizing the dangers of biological analogies in the past. Yet they do suggest a way in which their analysis could be useful for the present book on religious evolution:
At the very least, an analysis of evolvability by facilitated variation evokes different metaphors than does Social Darwinism, which stressed selective conditions, not variation. History is not just a product of selection, determined by the external environment or competition; it is also about the deep structure and history of societies. It includes their organizations, their capacity to adapt, their capacity to innovate, perhaps even their capacity to harbor cryptic variation and diversity.46
I mentioned in the Preface and will develop further below Merlin Donald’s scheme of cultural evolution as involving successively the emergence of mimetic, mythic, and theoretic culture.47 Perhaps each of these is a “conserved core process,” never lost even though reorganized in the light of new core processes, each promoting variation, adaptive and innovative, but each essential to cultural integrity. That comes close to stating the central argument of this book.
Parenthetically, I might note that even Kirschner and Gerhart, in their novel and challenging analysis of conservation and variation, cannot avoid the question of religion. They actually begin their book by referring to William Paley’s Natural Theology of 1809, where Paley develops the analogy of finding a watch on the heath and knowing that so complicated a mechanism had to have a maker, thus proving that the earthworm and the skylark must have had a maker too, what would later be called creationism. Our authors point out that the watch analogy is flawed: watches can be “made,” can be taken apart and reassembled, but organisms grow and, if taken apart, die. Darwin had Paley in mind when he developed his idea of all life as descended from a single beginning and changing through natural selection. 4’ But at the end of the book the authors “return to the heath” and imagine a descendant of Paley’s, with an education in modern biology, who could explain to her ancestor if they could converse, how the watch analogy doesn’t work and how we can understand the evolution of organisms in their own terms without the need of external intervention. But the authors do not want to exclude the question of faith; they simply want their young descendant to explain to her ancestor that we must now “draw the line between faith and science at a different place, one more defensible in the light of the modern understanding.“49 It seems, even when I don’t expect it, that the relation of science and religion appears time and time again in the writings of the scientists I have been studying. Later in this chapter I will sum up what I have, quite unintentionally, discovered about the many ways in which scientists have of late thought about religion in relation to their own work.
The Evolution of New Capacities
Maynard Smith and Szathmary in describing “transitions” and Kirschner and Gerhart in describing “conserved core processes” are both talking about the acquisition of new capacities. Stephen Jay Gould, in his opposition to the idea of progress in evolutionary history and his unhappiness with talk of higher and lower forms of life, quotes Darwin to similar effect and notes that Darwin for a long time avoided the word “evolution,” preferring to speak of “natural selection” instead, because “evolution” had the built-in meaning of progress, as so clearly in the case of Herbert Spencer. In Origin of Species Darwin speaks of progressive change as a “vague and ill-defined sentiment” among He accepts the idea only in the sense that descendants, due to the gradual accumulation of numerous small improvements, are more fitted for their environment than their ancestors and therefore more capable of surviving, though they too will in all likelihood become extinct. It seems that what worried Darwin was the idea of any inherent force for progress other than the slow workings of natural selection.” But perhaps it is possible to speak of the acquisition of n
ew capacities simply as a fact in evolutionary history, however those capacities have been acquired, without implying any metaphysical direction, and recognizing that the preponderance of bacteria in the world today is not only evidence of their fitness, but, in their own way, of their progress, of their ability to adapt to the most amazing range of environments. They have made excellent use of the capacities they have, and they have had no need of the capacities that developed later.
If we may pick up from the point of Kirschner and Gerhart’s final conserved core processes, the body plans of animals, twigs on the bush of life in which we happen to be very interested, we may note that in the early history of body plans, those of reptiles and mammals seem to be very similar. The earliest history of reptiles and mammals, some 320 million years ago (mya), more or less, is not entirely clear. Some classifications place the mammals as early descendants of reptiles, whereas others see both reptiles and mammals as diverging more or less at the same time from amniotes. In any case the early history of reptiles and mammals shows the clear predominance of reptiles. Large reptiles predominated in the Permian period (290-250 mya), though they were very nearly wiped out in the greatest extinction event known, the Permian Triassic extinction event. However, the reptiles made a comeback, and the “age of the dinosaurs,” as every schoolchild knows, followed. The dinosaurs were the dominant terrestrial animal from the late Triassic (about 230 mya) to the end of the Cretaceous (about 65 mya), when the Cretaceous-Tertiary extinction event finally wiped them out altogether, except for their descendants, the birds.
Religion in Human Evolution: From the Paleolithic to the Axial Age Page 11
