I Have Landed

by Stephen Jay Gould

  Second, the substitution of differentiation for addition also suggests that the author of Genesis 1 probably conceived the nature of plants in a manner radically different from our understanding today. We make a primary distinction between organic and inorganic, with plants unambiguously in the first category, although usually relegated to the bottom of a rising sequence of plant, animal, and human. (Sometimes, vernacular language even restricts “animal” to mammals alone—as in a kiddie card game called “Bird, Fish, Animal,” which I, as a professional biologist, simply couldn’t fathom until I thumbed through the deck and realized that “animal” only meant lions and tigers and bears, oh my!—and then the name of the game just drove me nuts. I shall die content if I ever persuade the manufacturers to rechristen this otherwise harmless and even instructive recreation as “Bird, Fish, Mammal.”) Our conventional taxonomy of organic and inorganic reinforces the false view that Genesis 1 should be read as a tale of addition—for primitive plants on day three should originate before any more advanced animal on day five. But why, then, does the intervening day four neglect organisms altogether?

  However, when we reinterpret Genesis 1 as a differentiation myth, an alternate taxonomy best explains the discontinuity between an appearance of plants on day three and the creation of a sequence of animals that begins on day five and then continues, with no further break, right to the end of the story. Day three, with both vertical and horizontal divisions in San Marco’s narthex, marks the episode of differentiation for the earth’s physical potential—the separation of the primal chaos below the firmament into its major components of water and land. The subsequent origin of plants on the same day (and in the next verse) suggests to me that the author of Genesis 1 viewed plants as the culminating aspect of the land’s differentiation, and not as a later addition from a separate organic realm, merely rooted within the substrate of another category of material stuff. In short, I would bet that the taxonomy of Genesis 1 intends to rank plants with earth, and not with animals.

  In advocating the importance of ancient creation myths for our modern understanding of natural history, I make no argument about truth value. Rather, I think that our primal myths teach us something important about the limits and capacities of the human mind for organizing complex material into sensible stories. All cultures must generate creation myths; how else can we infuse order into the buzzing and blooming confusion of nature’s surrounding diversity and complexity? Anthropologists, ethnographers, and folklorists have long noted the striking similarities among creation stories devised by people living in distant lands and without any known contact.

  Two explanations for these similarities have generally been offered: (1) perhaps the story really arose only once, and then passed from one culture to another by more efficient routes of sharing than anthropologists have recognized; or (2) perhaps the stories arose in true independence, but with striking similarity enforced by inherited mental preferences and images—the archetypes of Jungian psychology—deeply and innately embedded in the evolutionary construction of the human brain. But I think that we should add a third possibility, invoking logical limits to the structure of stories rather than explicitly similar content, derived either by direct transfer or evoked from common residence in all human brains. (Of course, such logical limits also lie within our mentality, but this third principle calls upon a different and much more general aspect of consciousness than the specific images of Jungian archetypes.) After all, comprehensible stories can only “go” in a certain number of ways—and the full list of creation myths, independently devised by our varied and separate cultures all over the globe, includes so many entries that, inevitably, several specific tales must fall under each of the few general rubrics.

  These themes, although far fewer than the stories that they must organize, still span a fairly ample range. For example, creation stories may be primarily elitninative, as when a promiscuous creator begins by populating the cosmos with all conceivable forms, and then lets nature take its course by weeding out the malformed and the nonoperational. Or creation stories may be cyclical, when sets of fully adequate orders successively succumb as new generations arise to enjoy their own transient ascendancy—so the Gods of Jupiter’s generation succeed their Saturnian ancestors, while Wotan and his cohort perish in Wagner’s Götterddämmerung, as a new day dawns at the end of four very long operas.

  But only two basic alternatives exist when a culture chooses to organize a creation myth as a successive and progressive series—surely a common, if not the preferred, theme among most human groups (for whatever set of complex reasons involving both mental preferences and natural appearances). Such tales of sequential improvement may invoke either successive addition (first make this, then add this at a higher level, etc.) or refining differentiation (start with a big soup containing all eventual products as unformed potential, and then separate-coagulate-harden, separate-coagulate-harden, etc.). Perhaps other alternatives exist, and creation myths certainly can (and usually do) include aspects of both primal tales. But addition and differentiation define the primary mental territory of creation myths constructed under the theme of sequential progression.

  I now reach the point of necessary confession for my cryptic and self-indulgent title. You have probably excused me for the narthex part, already explained above. But “pangenetic,” and the resulting totality in particular, require an abject plea for your indulgence. In using “pangenetic,” first of all, I honor my hero, and the inspiration for all ten volumes in this series of essays, Charles Darwin. In his longest book of 1868, the two-volume Variation of Animals and Plants under Domestication, Darwin proposed, as a “provisional hypothesis” in his own words and judgment, a theory of heredity that he called pangenesis. History has forgotten this incorrect theory, both rightly and entirely—although, curiously and by a complex route, our most salient modern word gene explicitly honors Darwin’s failed effort.

  According to pangenesis, each organ of the body casts off tiny particles called gemmules. These gemmules circulate throughout the body, and each sex cell eventually accumulates a full set. Thus the fertilized egg contains a complete array of determinants for growing all parts of the adult body—and embryology becomes a process of making these gemmules manifest and letting them grow. In other words, pangenesis expresses a pure theory of differentiation rather than addition for the explanation of organic development. The initial fertilized cell (like the primal chaos of Genesis 1) includes all components of the complex adult, but in unexpressed and inchoate form. Embryology then unfolds as the realization of an initially unformed but completely self-contained potential. Thus the pangenetic paradigm, honoring Darwin’s version of a larger theme, encompasses a class of models based on differentiation rather than addition for the generation of progressive complexity in a temporal series. And the creation story, as depicted in San Marco’s narthex, clearly lies within this pangenetic class.

  Now for the self-indulgent part: the most widely cited technical paper that I ever wrote (with the exception of my first article on punctuated equilibrium, coauthored with Niles Eldredge) bore the title “The spandrels of San Marco and the Panglossian paradigm” (written with my colleague Dick Lewontin, the smartest man I have ever known). For a variety of reasons happily irrelevant to the subject of this essay, the spandrels paper has been unmercifully attacked by a substantial group of biologists committed to the strictly adaptationist account of evolution that this paper questions. (Our spandrels paper has also been appreciated, I trust, by an even more substantial group of colleagues, both in numbers and perspicacity!) Among the many published attacks, several have parodied our original title—as in “the scandals of San Marco” and even “the spaniels of St. Marx.” So I thought I’d indulge myself, after all this tsuris, by writing a paper with my own title parody, albeit on a quite different subject. Sorry, folks, but at least I have laid down all my cards—and I now bare my throat.

  I have little doubt that the first three days of Genesis
1 should be read as a tale of differentiation rather than addition. I also tend to view the fourth day as a continuation in the same mode—that is, God differentiates the earth below into water and land (with plants) on the third day and then, on the fourth day, differentiates the light of the sky above into sun, moon, and stars. But I must confess mixed feelings and signals about the fifth and sixth days. Does God now switch modes to utilize the alternative theme of addition in populating a cosmos (prepared by differentiation) with living creatures? Or does the origin of animals continue the theme of differentiation—as the air and water precipitate their living counterparts on day five, while the land generates its own appropriate forms of life on day six?

  The scene of Adam’s creation in San Marco’s narthex might be read as support for the continuing theme of differentiation. Adam arises, dark as the soil, from the substrate of his origin—brought forth from the earth (the literal meaning of Adam in Hebrew), rather than imposed upon the earth as a separate creation from astral realms. (A familiar Latin pun—homo ex humo (man from the earth)—expresses the same thought, as does the old injunction “for dust thou art, and unto dust shalt thou return.”)

  My own, utterly nonscholarly, intuitions lead me to view the first four days as pure differentiations: light divided from darkness on day one, the upper water of rain from the lower water of rivers and lakes on day two, land from sea on the earth of day three, and sun from moon (the coagulation of previously diffuse light) in the heavens of day four. I then view days five and six as, in part, emplacements (more additive than differentiative) into appropriate surroundings, but also as the final differentiations of each realm—as water, air, and land all bring forth their appropriate living expressions.

  Other interpretations abound, of course. In one popular scheme, advocated in two books that I have read and in several letters received from readers of these essays, the six days of creation fall into two equal cycles: three days of preparation followed by three days of population (of the heavens by sun, moon, and stars on day four; of the sea and air by swimming and flying animals on day five; and of the earth by terrestrial animals and humans on day six). In this reading, one might view the first three days as differentiative (whereas I would so interpret the first four days under this theme), and the last three as primarily additive. Nonetheless, however one explicates the story, I don’t see how our usual reading of progressive addition for all six days can possibly be supported. At least the first three days—probably the first four, and perhaps all six—must be reconceived as a creation myth based on the great alternative theme of differentiation from unformed potential, rather than addition piece by piece.

  This contrast of differentiation and addition as the two primary modes of organizing stories about sequential and progressive development becomes relevant to students of natural history not only as a framework for analyzing our oldest classics of the discipline (the creation myths in our earliest historical documents), but also as a guide to understanding our current problems and conflicts. In particular, when we recognize that we do not derive our concepts of history only from the factual signals that scientific research has extracted from nature, but also from internal limits upon the logical and cognitive modes of human thought, then we can appreciate the complex interaction of mind and nature (or inside and outside) that all great theories must embody.

  The ancient creation myths of our cultures become particularly interesting in this context because they originated when our ancestors possessed no direct data at all about the actual pathways of life’s history as revealed in the fossil record. These myths therefore represent nearly pure experiments in the range of mental possibilities for explaining the natural world when no hard information constrained our field of speculation.

  The “bottom line” or “take home” message—that mind and nature always interact to build our basic concepts of natural order—becomes especially relevant in our current scientific age, where prevailing beliefs about the sources of knowledge lead us to downplay the role of the mind’s organizing potentials and limits, and therefore encourage us to regard our theories of nature as products of objective observation alone. In particular, the logical restriction of tales about sequential and progressive development to two basic modes—differentiation and addition in the terms of this essay—can help us to understand our current theories (and to probe their scientific weaknesses when our mental preferences have hidden a different factual reality).

  Consider the two major processes in biology—embryology and evolution—that, when specifically applied to human history, will inevitably be depicted as tales of sequential development toward greater complexity. (I do not believe that either process, especially evolution, must yield stories in this mode, but I do not challenge this pattern for our own particular case.) Both the history and current array of views on human embryology and evolution may be regarded, without gross caricature or oversimplification, as one long exercise in the interplay of shifting preferences for stories about differentiation or addition.

  The study of vertebrate embryology, from the invention of the microscope in the seventeenth century to our modern understanding of genetics, has featured a set of debates between differentiative and additive stories for a process of increasing size and complexity from a tiny homogeneous egg to a neonate with all the anatomical complexity of adulthood. During most of the seventeenth and eighteenth centuries, the debate between “epigenesis” and “preformationism” virtually defined the territory of study for embryology. The epigeneticists embraced an additive model, arguing that the initial egg should be interpreted as its literal appearance suggests—that is, merely as a mass of promiscuous potential, devoid of structure, and eventually shaped to the particular anatomy of the complex neonate only because formative principles then operate upon this initial homogeneity to build, step by step and in an unerring manner (so long as embryology follows its normal course) the complexity of the final product. (Epigenesis means, literally, “generated upon”—that is, one step after the other.)

  By contrast, the preformationists rallied behind a story of differentiation that envisaged all the structural complexity of the neonate as already present within the initial cell, and only brought to visibility during embryology. In the caricatured version, preformationism has usually been ridiculed as the belief that a perfect homunculus lies within each sperm or egg cell. No serious scientific preformationist held such a view. Rather, they argued that all structures must be present in the initial cell, but in too tiny, too transparent, and too diffuse a state to be visible (like the chaos at the outset of Genesis 1, and not like a fully formed homunculus). Embryology then becomes a differentiative process of concentration, coagulation, solidification, and growth.

  When evolutionary ideas pervaded embryology in the nineteenth century, the two leading interpretations continued to uphold contrasting stories of addition or differentiation. Haeckel’s famous theory of recapitulation held, in a purely additive account, that sequential steps in embryonic complexification repeated the evolutionary accretion of successive adult stages to the ancestral lineage—so that a complex animal, in its embryology, literally climbed its own family tree. The primary alternative, von Baer’s theory of differentiation, argued that the visual simplicity of an early stage does not represent an ancient ancestor that must then be augmented (as in Haeckel’s additive theory), but rather a more general form of greater homogeneity and lesser differentiation, holding all potential for the definitive complexity that eventually develops in each lifetime. Thus, at an early stage of development, we know that the embryo will become a vertebrate, then (at a later stage) a mammal, then a primate, then a hominoid, and finally a human being—a process of increasingly finer specification, contrasted with Haeckel’s additive model of ever-increasing complexity in accretion.

  When we consider the other historical process that led to our human form—the much longer evolutionary construction of Homo sapiens in geological time, rather than the embryological gener
ation of each individual Homo sapiens in nine months—we note that concepts of evolution may also be classified into additive and differentiative models. Darwinism embodies an additive view. Because the Darwinian style of explanation has prevailed within science, we tend to forget that several abandoned theories of evolution advocated differentiative models. These accounts imagined that the first vertebrate in the Cambrian explosion—a boneless and jawless creature just an inch or two in length—already contained all the parts and potentials that evolution would necessarily elaborate into human form in a distant future. The supposed mechanisms for such a “programmed” differentiation spanned the full gamut from God’s direct actions (in a few overtly theological accounts) to principles embodied in unknown, but entirely physical, laws of nature (for some atheistic versions at an opposite speculative extreme).

  If allegiance to an additive or differentiative model implied no consequences for skewing our views of life in disparate directions, then we could dismiss the entire subject as an effete intellectual game without meaning for scientific understanding. But our preferred theories often act as biases that strongly influence our basic conceptions of the natural world—and additive versus differentiative views of historical sequences do not hold the same intellectual weights, properties, and implications. We might summarize the differences, looking at lessons from the history of science, by saying that each basic model features a defining property and struggles with a major problem.