Purpose and desire, p.12
Purpose and Desire, page 12
Taken alone, Cope’s question sounds cryptic, but it makes better sense in the context of his theory of bathmism properly understood. Cope was a vitalist, in the same sense that Claude Bernard was: he regarded life as a unique phenomenon in the universe, which demanded a unique mode of understanding. Where Bernard focused on homeostasis as life’s distinct quality, Cope sought to frame the question in terms of energy, which led him to a surprisingly advanced theory of evolution—and of orthogenesis. He argued that there was a competition between two forms of work in the universe. Anagenesis, or order-producing work, would fuel growth and complexity. Anagenesis was balanced against work that drove matter toward disorder and death—that is, katagenesis, or degradation to entropy and equilibrium. Cope regarded living systems as anagenesis prevailing over katagenesis. In nonliving systems, the prevalence was reversed: katagenesis prevailed over anagenesis. Bathmism, or growth-energy, was what tilted the prevalence in living systems toward anagenesis.
Strip away the funny neologisms, and it is clear that Cope would have been quite at home with the parable of the cauliflower and cumulus cloud introduced in the Preface. No one pays attention to Cope these days, though, because Cope’s theory marks him as both a Lamarckian and a vitalist: two strikes in the modern Darwinian mind. Strike three came because Cope saw no reason to draw a distinction between soma and germ line as Weismann had done. If the principle of bathmism applied to individual creatures, as Cope had asserted it does, on what basis can we say that it could not also apply to lineages? Both are expressions of life, and if bathmism helps explain one aspect, why should it not explain all aspects? In this, Cope was rowing against the tide, as Cope always did. Whether he was right or wrong in doing so depends, of course, on the strength of his critics’ arguments.
Which brings us back to Weismann’s barrier.
We can chuckle at Cope’s quaint terminology and his flirtation with Lamarckism and vitalism, but the fact is that the Darwinists in Cope’s time had no better answer. But wait, you might say, didn’t Weismann put all that to rest with his impenetrable barrier? As it turns out, the Weismann barrier was not something that was demonstrated with beautiful experiments and empirical proof. Rather, it was a logical necessity that followed from Weismann’s own totally erroneous theory of embryonic development.
In the developing embryo, a kind of evolution is at work.* The question that consumed Weismann was how the embryo’s diverse tissues and cells could arise from the single zygote: differentiation, in a word. Weismann was convinced that differentiation was governed by a kind of hereditary particle, which his observations had located as residing in the cell’s nucleus. The zygote’s nucleus thus contained within it the hereditary particles that could determine the fates of the zygote’s innumerable descendants. The problem Weismann grappled with was how the same set of hereditary particles in the zygote could produce such diverse outcomes in its descendants.
Weismann had a curious name for these particles—he called them ids.* Innumerable ids were contained within the zygote’s nucleus, constituted from ids contributed equally by the mother and father, and a cell’s characteristics were determined by its collection of ids. There were muscle ids, brain ids, skin ids, and so forth, all contained within the zygote’s nucleus, ready to act. Ids could also be either active or dormant and could be wakened by various undefined forces operating within the cells (vital forces seem to creep in everywhere).
So far, Weismann’s conception of the id is looking a lot like our modern conception of the gene, and in fact Weismann’s id inspired the formal definition of the gene that would come at the end of the nineteenth century.* Where Weismann went wrong was his conception of how the innumerable ids in the zygote came to determine the many different cell types in the embryo.
Figure 6.7
Weismann’s conception of embryonic differentiation and development. Heredity was carried on particles that Weismann called ids. These were present in active forms (circles) or inactive forms (squares). Differentiation involved the selective destruction of ids, leaving a subset of ids that defined the differentiated cell. Reproduction involved the transmission of form from one generation (n) to the next (n+1), which meant transmitting a complete collection of ids.
Weismann’s conception is a little complicated but easy to grasp if we follow what happens to four hypothetical ids: for muscle, brain, skin, and bone. At conception, all ids are present in inactive form in the zygote (indicated by the square symbols in Figure 6.7), and these are transmitted in their inactive forms during the zygote’s first few cell divisions, what is known as the cleavage stage. During cleavage, the zygote rapidly divides several times, copying its collection of inactive ids into several cells as it does, including one set that is to be segregated into the germ line. The Weismann barrier starts at this point.
What follows is growth of the embryo and differentiation of the various lineages of the cellular descendants of the zygote. As these cells continue to divide, they pass on their collection of ids. As the various lineages differentiate, ids become active (indicated by the circular symbols in Figure 6.7). Differentiation is possible, though, only if one type of id is activated in a lineage. Muscle cells, for example, are muscle cells because only muscle ids are activated within them. Weismann thought that various ids were selectively destroyed through the progress of a cell lineage toward differentiation and specialization, so that only one type of id would remain in the cells of a differentiated tissue. In muscle tissue, for example, all the ids handed down from the zygote except for muscle ids would be eliminated from the cellular lineage (indicated by the triangular symbols in Figure 6.7). The same would be true for brain tissue: all ids except brain ids would be eliminated, and so forth for all the differentiated cell types. The soma comprises all these differentiated lineages, and all these lineages eventually die.
Weismann came to this model not because he had any positive evidence for it, but because he had a hunch: he thought it absurd that the mature differentiated cells of the soma would carry all the zygote’s ids. As Weismann put it:
It is highly improbable that all the determinants in the id of germ-plasm are carried along through all the idic stages of the ontogeny [i.e., those stages of embryonic development where differentiation is occurring]. . . . Why should Nature, who always manages with economy, indulge in the luxury of providing all the cells of the body with the whole of the determinants of the germ-plasm if a single kind of them is sufficient?14
As it turns out, Weismann was wrong in his hunch. If we equate the id with the gene, as came to be the case, we now know that every cell in the body carries the same genes as the zygote, indulging in the very luxury that Weismann thought absurd. Differentiation comes from the different tissues expressing different suites of that complete collection of genes and silencing others—muscle cells express a different suite of genes than brain cells do—but all cells contain the same collection of genes as the zygote. In short, there is no selective destruction of ids during embryonic differentiation, as Weismann thought had to be the case.
Nevertheless, Weismann’s assumption was enormously consequential, because the logic of his selective destruction of ids leads directly to the twin doctrines of the segregation of the germ line and the Weismann barrier. The logical chain is quite simple. None of the differentiated cells in the soma could be suitable candidates for the soma’s reproduction, because none of the somatic cells carried within them contain the complete collection of ids that would be required for successful reproduction. The consequence of differentiation therefore is ultimate irrelevance and death of the soma. Successful reproduction, in contrast, could only come from a set of cells set aside early in embryonic life that retained a complete set of the organism’s ids: the segregated germ line. Furthermore, these privileged cells could not be permitted to participate in the normal life of the soma, because allowing them to do so would risk breaking up the complete set of ids that would be necessary for the organism’s successful reproduction. They therefore had to be segregated from the soma: the logic of Weismann’s model of development demanded it. Successful reproduction could come only from gametes passing on a complete set of ids to the next generation. Evolution within the soma—what we now call physiological adaptation or phenotypic plasticity—could occur, but this could in no way influence the ids in the segregated germ line, because that would imperil the integrity of the complete collection of ids held there. Evolution of the lineage, in contrast, could come about only from modification of the ids of the germ line.
It was on this flimsy foundation that the wedge was driven that would cleave modern biology to the present day—the wedge between soft and hard inheritance, between physiological and evolutionary adaptation, between living body and the crystalline purity of gametes, between vital life and its clockwork imitation. The irony, of course, is that the Weismann barrier was erected not upon the foundation of a trivial experiment with mutilated mice, but on August Weismann’s deep knowledge of embryology, his subtle thoughts on the relationship between embryology and evolution, and his formidable logic. That logic turns out to have been wrong, and this means that the Weismann barrier—that scourge of Lamarckism, that foundation of modern evolution—is the barrier that wasn’t.
Weismann also set in motion the epistemic closure of modern Darwinism. Before Weismann, evolutionary thought had been concerned with the interplay between adaptation and heredity, between change and stasis, between soft and hard inheritance—Darwinism’s central dilemma, in other words. That is a very difficult dilemma to unravel, and much of the confusing turmoil of post-Darwinian evolutionism—the crisis of Darwinism—is testimony both to the complexity of the problem and to the richness of evolutionary thought at that time. After Weismann, Darwinism became a theory concerned solely with heredity, indeed with only one form of heredity: hard inheritance. Adaptation, the organism, all the messy complications that went along with the interplay of adaptation with heredity, became secondary, shoved to the back of everyone’s minds.
At this point, I want to introduce a word of caution, just to set the stage for what is to follow. I hope I have persuaded you that evolutionary thought in the late nineteenth century was very rich. One of the casualties of the epistemic closure of modern Darwinism has been the appreciation of just how intellectually rich that era was. The temptation is to conclude that modern Darwinism therefore has become intellectually impoverished by comparison. That would not be correct, because an epistemically closed world can also be incredibly rich. With epistemic closure, the boundaries of the playing field change, which has little to do with the brilliance of the play. LeBron James will play brilliant basketball whether he is playing full-court or half-court: he will just play brilliantly within different bounds. That is largely the case for the post-Weismann epistemic closure of evolutionism. There is much brilliance in there to appreciate, but the appreciation must be tempered by the realization that we are now watching half-court basketball.
7
The Reverse Pinocchio
In the Dutch city of Delft, behind the Nieuwe Kerk, stands a statue, The Milkmaid (Het Melkmeisje), Wim T. Schippers’s stucco-on-concrete representation of Johannes Vermeer’s famous painting of the same name (Figure 7.1). The statue and painting are each beautiful in their own ways. They both capture the milkmaid’s peasant solidity and her firm grounding (literally, in the case of the statue) in the everyday life of seventeenth-century Holland. Yet Vermeer’s painting seems somehow alive in a way that Schippers’s sculpture does not quite capture. Vermeer’s milkmaid bends her head down in rapt attention to her task, drawing our attention in as she takes care to not spill a single drop of milk as she pours. The painting so glows with vitality that the milkmaid seems about to step out of the canvas, off to do the next chore of her busy day. In contrast, Schippers’s milkmaid seems frozen in place, as if she was Lot’s unfortunate wife who looked up at Sodom at precisely the wrong moment. She stares off, mouth agog, through only hints of eyes, to some distant scene that has caught her attention.
Figure 7.1
The Milkmaid in stone (left: sculpture by Wim T. Schippers, 1975) and oil on canvas (right: Johannes Vermeer, ca. 1660).
This creative tension between the living and nonliving, between painting and stone, between the vital and the inanimate, permeated much of the development of evolutionary thought through the late nineteenth and early twentieth centuries. At stake was nothing less than the soul of biology: whether we would study life as a unique phenomenon to be understood by its own rules, or whether we would flatten life under the rules that govern the rest of the material universe. By the 1940s, the question was largely settled, for most, in favor of the latter. For those who had held out that life could be understood as something vital and unique, well—to lift the title of an essay by Tom Wolfe—sorry, but your soul just died.*
For those who had decided to embrace biology’s brave new world, the death of biology’s soul was like the death of a beloved pet in its dotage: lamented, an occasion for sad nostalgia perhaps, but a blessing in the end. Yet in that death were sown the seeds of biology’s impending crisis—a crisis that began building with the crisis of Darwinism, which, contrary to the received wisdom, was not settled at the turn of the twentieth century. Nor has it been settled by biology’s twentieth-century triumphant march to materialism. We may have been able to disguise it, but in fact, we are neck deep in the crisis still. We are neck deep in it because the crisis lies in the still-standing irresolution of Darwinism’s central paradox: the tension between adaptation and heritable memory.
In the post-Origin nineteenth century, the crisis largely played out in the interplay between hard inheritance and soft inheritance. Hard inheritance was the boot to the flank that drove life ahead under its pitiless command, while in soft inheritance reposed the hope that life somehow had control over itself after all. In the hopeful shelter of soft inheritance stood the Lamarckian theory of vital adaptation, that a life’s experience mattered across the generations as well as within them—a hope that was reflected in Darwin’s pangenesis idea.
This hope reverberated through biology into the first decades of the twentieth century, but it was fated ultimately to be crushed. The beginning of the end can be pegged to August Weismann’s decision to cast biology’s lot completely with hard inheritance, which set the scene for ushering adaptation off the stage, leaving only hard inheritance to command our thoughts. The final coup was delivered some thirty years later by another giant figure of twentieth-century biology, Thomas Hunt Morgan (1866–1945; Figure 7.2). Ironically, Morgan himself thought at the time he had killed off not only Darwinism for good, but Lamarckism as well. He was premature: as we shall see, the Darwinian idea was revived just a few years later by three brilliant thinkers who pulled off one of the greatest scientific achievements of twentieth-century science: the so-called genetical theory of natural selection. But as we shall also see, this did not resolve the crisis, it only deepened it.
Figure 7.2
Thomas Hunt Morgan in 1920.
Let us turn to Morgan first. Thomas Hunt Morgan is best remembered for his pioneering work on the genetics of the fruit fly, Drosophila melanogaster, literally the black-bellied fruit lover. Whenever biology students anywhere in the world are taught genetics, whether they are in high school or college, they take a vicarious stroll into Morgan’s famous “Fly Room” at Columbia University.* This is usually an exercise in tedium for students—many undergraduate science laboratory classes seem designed to maximize drudgery—but with some imagination, students can conjure the atmosphere of the Fly Room in their minds: its insistent smell of overripe bananas, the multitude of little bottles filled with breeding fruit flies, the maggots writhing through the nutritious mush, and the laborious sorting and counting of tiny fly offspring under the microscope. What is not often captured in the tedium of the classroom genetics laboratory is the heady intellectual atmosphere that must have pervaded the Fly Room, for also hatched in this tiny space were many of the most important minds of twentieth-century biology. One cannot read the accounts and reminiscences of the Fly Room alumni without seeing in their reflections the endearingly tatty beau idéal of the scientific life—egalitarian, rational, improvisational, nimble, experimental, interactive.*
Morgan is important to our story because he cemented into place Weismann’s radical division of physiological and evolutionary adaptation. What is ironic is that Morgan was a harsh critic of Weismann’s scientific thought. To be fair, Morgan was a harsh critic of the scientific thought of nearly everyone besides himself, even of Charles Darwin. This contradiction is essential to understanding many of the tangled roots of modern Darwinism, for with Morgan came full epistemic closure on the matter. Once the evolutionist episteme closed, no role for soft inheritance could even be conceivable, rendering it effectively invisible. With the closure began the ultimate alienation of the science of life from life itself.
Morgan’s basic philosophy of science was positivist, which means that he believed that valid knowledge could only come from experimental demonstration and test. All else was irritating “speculation” and intellectually suspect, and Morgan found many reasons to be irritated with the biology of his time. Weismann’s ids were the particular source of Morgan’s irritation with him, and the inchoate strivings proposed by the Lamarckians (and to a large extent, the pre-Weismann Darwinians) were another. Outside Morgan’s positivist world, natural history was mere storytelling, taxonomy was stamp collecting, and paleontology was infested with entrenched Lamarckians like the impossible Cope.
