The Panda's Thumb: More Reflections in Natural History

by Stephen Jay Gould

  Haeckel defined his moneran as “an entirely homogeneous and structureless substance, a living particle of albumin, capable of nourishment and reproduction.” He proposed the moneran as an intermediate form between non-living and living. He hoped that it would solve the vexing question of life’s origin from the inorganic, for no problem seemed thornier for evolutionists and no issue attracted more rear-guard support for creationism than the apparent gap between the most complex chemicals and the simplest organisms. Haeckel wrote: “Every true cell already shows a division into two different parts, i.e., nucleus and plasm. The immediate production of such an object from spontaneous generation is obviously only conceivable with difficulty; but it is much easier to conceive of the production of an entirely homogeneous, organic substance, such as the structureless albumin body of the Monera.”

  During the 1860s, the identification of monerans assumed high priority on the agenda of Darwin’s champions. And the more structureless and diffuse the moneran, the better. Huxley had told Kingsley that he would follow facts into a metaphorical abyss. But when he examined a true abyss in 1868, his hopes and expectations guided his observations. He studied some mud samples dredged from the sea bottom northwest of Ireland ten years before. He observed an inchoate, gelatinous substance in the samples. Embedded in it were tiny, circular, calcareous plates called coccoliths. Huxley identified his jelly as the heralded, formless moneran and the coccoliths as its primordial skeleton. (We now know that coccoliths are fragments of algal skeletons, which sink to the ocean bottom following the death of their planktonic producers.) Honoring Haeckel’s prediction, he named it Bathybius Haeckelii. “I hope that you will not be ashamed of your godchild,” he wrote to Haeckel. Haeckel replied that he was “very proud,” and ended his note with a rallying cry: “Viva Monera.”

  Since nothing is quite so convincing as an anticipated discovery, Bathybius began to crop up everywhere. Sir Charles Wyville Thomson dredged a sample from the depths of the Atlantic and wrote: “The mud was actually alive; it stuck together in lumps, as if there were white of egg mixed with it; and the glairy mass proved, under the microscope, to be a living sarcode. Prof. Huxley…calls it Bathybius.” (The Sarcodina are a group of single-celled protozoans.) Haeckel, following his usual penchant, soon generalized and imagined that the entire ocean floor (below 5,000 feet) lay covered with a pulsating film of living Bathybius, the Urschleim (original slime) of the romantic nature philosophers (Goethe was one) idolized by Haeckel during his youth. Huxley, departing from his usual sobriety, delivered a speech in 1870 and proclaimed: “The Bathybius formed a living scum or film on the seabed, extending over thousands upon thousands of square miles…it probably forms one continuous scum of living matter girding the whole surface of the earth.”

  Having reached its limits of extension in space, Bathybius oozed out to conquer the only realm left—time. And here it met our second chimera.

  Eozoon canadense, the dawn animal of Canada, was another organism whose time had come. The fossil record had caused Darwin more grief than joy. Nothing distressed him more than the Cambrian explosion, the coincident appearance of almost all complex organic designs, not near the beginning of the earth’s history, but more than five-sixths of the way through it. His opponents interpreted this event as the moment of creation, for not a single trace of Precambrian life had been discovered when Darwin wrote the Origin of Species. (We now have an extensive record of monerans from these early rocks, see essay 21.) Nothing could have been more welcome than a Precambrian organism, the simpler and more formless the better.

  In 1858, a collector for the Geological Survey of Canada found some curious specimens among the world’s oldest rocks. They were made of thin, concentric layers, alternating between serpentine (a silicate) and calcium carbonate. Sir William Logan, director of the Survey, thought that they might be fossils and displayed them to various scientists, receiving in return little encouragement for his views.

  Logan found some better specimens near Ottawa in 1864, and brought them to Canada’s leading paleontologist, J. William Dawson, principal of McGill University. Dawson found “organic” structures, including a system of canals, in the calcite. He identified the concentric layering as the skeleton of a giant foraminifer, more diffusely formed but hundreds of times larger than any modern relative. He named it Eozoon canadense, the Canadian dawn animal.

  Darwin was delighted. Eozoon entered the fourth edition of the Origin of Species with Darwin’s firm blessing: “It is impossible to feel any doubt regarding its organic nature.” (Ironically, Dawson himself was a staunch creationist, probably the last prominent holdout against evolution. As late as 1897, he wrote Relics of Primeval Life, a book about Eozoon. In it he argues that the persistence of simple Foraminifera throughout geologic time disproves natural selection since any struggle for existence would replace such lowly creatures with something more exalted.)

  Bathybius and Eozoon were destined for union. They shared the desired property of diffuse formlessness and differed only in Eozoon’s, discrete skeleton. Either Eozoon had lost its shell to become Bathybius or the two primordial creatures were closely related as exemplars of organic simplicity. The great physiologist W. B. Carpenter, a champion of both creatures, wrote:

  If Bathybius…could form for itself a shelly envelope, that envelope would closely resemble Eozoon. Further, as Prof. Huxley has proved the existence of Bathybius through a great range not merely of depth but of temperature, I cannot but think it probable that it has existed continuously in the deep seas of all geological epochs…. I am fully prepared to believe that Eozoon, as well as Bathybius, may have maintained its existence through the whole duration of geological time.

  Here was a vision to titillate any evolutionist! The anticipated, formless organic matter had been found, and it extended throughout time and space to cover the floor of the mysterious and primal ocean bottom.

  Before I chronicle the downfall of both creatures, I want to identify a bias that lay unstated and undefended in all the primary literature. All participants in the debate accepted without question the “obvious” truth that the most primitive life would be homogeneous and formless, diffuse and inchoate.

  Carpenter wrote that Bathybius was “a type even lower, because less definite, than that of Sponges.” Haeckel declared that “protoplasm exists here in its simplest and earliest form, i.e., it has scarcely any definite form, and is scarcely individualized.” According to Huxley, life without the internal complexity of a nucleus proved that organization arose from indefinite vitality, not vice versa: Bathybius “proves the absence of any mysterious power in nuclei, and shows that life is a property of the molecules of living matter, and that organization is the result of life, not life the result of organization.”

  But why, when we begin to think about it, should we equate formless with primitive? Modern organisms encourage no such view. Viruses are scarcely matched for regularity and repetition of form. The simplest bacteria have definite shapes. The taxonomic group that houses the amoeba, that prototype of slithering disorganization, also accommodates the Radiolaria, the most beautiful and most complexly sculpted of all regular organisms. DNA is a miracle of organization; Watson and Crick elucidated its structure by building an accurate Tinkertoy model and making sure that all the pieces fit. I would not assert any mystical Pythagorean notion that regular form underlies all organization, but I would argue that the equation of primitive with formless has roots in the outdated progressivist metaphor that views organic history as a ladder leading inexorably through all the stages of complexity from nothingness to our own noble form. Good for the ego to be sure, but not a very good outline of our world.

  In any case, neither Bathybius nor Eozoon outlived Queen Victoria. The same Sir Charles Wyville Thomson who had spoken so glowingly of Bathybius as a “glairy mass…actually alive” later became chief scientist of the Challenger expedition during the 1870s, the most famous of all scientific voyages to explore the world’s oceans. The C
hallenger scientists tried again and again to find Bathybius in fresh samples of deep-sea mud, but with no success.

  When scientists stored mud samples for later analysis, they traditionally added alcohol to preserve organic material. Huxley’s original Bathybius had been found in samples stored with alcohol for more than a decade. One member of the Challenger expedition noticed that Bathybius appeared whenever he added alcohol to a fresh sample. The expedition’s chemist then analyzed Bathybius and found it to be no more than a colloidal precipitate of calcium sulfate, a product of the reaction of mud with alcohol. Thomson wrote to Huxley, and Huxley—without complaining—ate crow (or ate leeks, as he put it). Haeckel, as expected, proved more stubborn, but Bathybius quietly faded away.

  Eozoon hung on longer. Dawson defended it literally to the death in some of the most acerbic comments ever written by a scientist. Of one German critic, he remarked in 1897: “Mobius, I have no doubt, did his best from his special and limited point of view; but it was a crime which science should not readily pardon or forget, on the part of editors of the German periodical, to publish and illustrate as scientific material a paper which was so very far from being either fair or adequate.” Dawson, by that time, was a lonely holdout (although Kirkpatrick of essay 22 revived Eozoon in a more bizarre form later). All scientists had agreed that Eozoon was inorganic—a metamorphic product of heat and pressure. Indeed, it had only been found in highly metamorphosed rock, a singularly inauspicious place to find a fossil. If any more proof had been needed, the discovery of Eozoon in blocks of limestone ejected from Mount Vesuvius settled the issue in 1894.

  Haeckel’s original illustration of Bathybius. The discoidal structures are coccoliths in the gelatinous mass.

  Bathybius and Eozoon, ever since, have been treated by scientists as an embarrassment best forgotten. The conspiracy succeeded admirably, and I would be surprised if one percent of modern biologists ever heard of the two fantasies. Historians, trained in the older (and invalidated) tradition of science as a march to truth mediated by the successive shucking of error, also kept their peace. What can we get from errors except a good laugh or a compendium of moral homilies framed as “don’ts”?

  Modern historians of science have more respect for such inspired errors. They made sense in their own time; that they don’t in ours is irrelevant. Our century is no standard for all ages; science is always an interaction of prevailing culture, individual eccentricity, and empirical constraint. Hence, Bathybius and Eozoon have received more attention in the 1970s than in all previous years since their downfall. (In writing this essay, I was guided to original sources and greatly enlightened by articles of C. F. O’Brien on Eozoon, and N. A. Rupke and P. F. Rehbock on Bathybius. The article by Rehbock is particularly thorough and insightful.)

  Science contains few outright fools. Errors usually have their good reasons once we penetrate their context properly and avoid judgment according to our current perception of “truth.” They are usually more enlightening than embarrassing, for they are signs of changing contexts. The best thinkers have the imagination to create organizing visions, and they are sufficiently adventurous (or egotistical) to float them in a complex world that can never answer “yes” in all detail. The study of inspired error should not engender a homily about the sin of pride; it should lead us to a recognition that the capacity for great insight and great error are opposite sides of the same coin—and that the currency of both is brilliance.

  Bathybius was surely an inspired error. It served the larger truth of advancing evolutionary theory. It provided a captivating vision of primordial life, extended throughout time and space. As Rehbock argues, it played a plethora of roles as, simultaneously, lowliest form of protozoology, elemental unit of cytology, evolutionary precursor of all organisms, first organic form in the fossil record, major constituent of modern marine sediments (in its coccoliths), and source of food for higher life in the nutritionally impoverished deep oceans. When Bathybius faded away, the problems that it had defined did not disappear. Bathybius inspired a great amount of fruitful scientific work and served as a focus for defining important problems still very much with us.

  Orthodoxy can be as stubborn in science as in religion. I do not know how to shake it except by vigorous imagination that inspires unconventional work and contains within itself an elevated potential for inspired error. As the great Italian economist Vilfredo Pareto wrote: “Give me a fruitful error any time, full of seeds, bursting with its own corrections. You can keep your sterile truth for yourself.” Not to mention a man named Thomas Henry Huxley who, when not in the throes of grief or the wars of parson hunting, argued that “irrationally held truths may be more harmful than reasoned errors.”

  24 | Might We Fit Inside a Sponge’s Cell

  I SPENT DECEMBER 31, 1979 reading through a stack of New York Sunday papers for the last weekend of the decade. Prominently featured, as always in the doldrums of such artificial transition, were lists of predictions about “ins” and “outs” across the boundary: what will the eighties reject that the seventies treasured? what, despised during the seventies, will the eighties rediscover?

  This surfeit of contemporary speculation drove my mind back to the last transition between centuries and to a consideration of biological ins and outs at this broader scale. The hottest subject of nineteenth-century biology did suffer a pronounced eclipse in the twentieth. Yet I happen to maintain a strong fondness for it. I also believe that new methods will revive it as a major concern for the remaining decades of our century.

  Darwin’s revolution led a generation of natural historians to view the reconstruction of life’s tree as their most important evolutionary task. As ambitious men embarked upon a bold new course, they did not focus narrowly upon little twiglets (the relation of lions to tigers), or even upon ordinary branches (the link between cockles and mussels); they sought to root the trunk itself and to identify its major limbs: how are plants and animals related? from what source did the vertebrates spring?

  In their mistaken view, these naturalists also possessed a method that could extract the answers they sought from the spotty data at their disposal. For, under Haeckel’s “biogenetic law”—ontogeny recapitulates phylogeny—an animal climbs its own family tree during its embryological development. The simple observation of embryos should reveal a parade of adult ancestors in proper order. (Nothing is ever quite so uncomplicated, of course. The recapitulationists knew that some embryonic stages represented immediate adaptations, not ancestral reminiscences; they also understood that stages could be mixed up, even inverted, by unequal rates of development among different organs. Yet they believed that such “superficial” modifications could always be recognized and subtracted, leaving the ancestral parade intact.) E.G. Conklin, who later became an opponent of “phylogenizing,” recalled the beguiling appeal of Haeckel’s law:

  Here was a method which promised to reveal more important secrets of the past than would the unearthing of all the buried monuments of antiquity—in fact nothing less than a complete genealogical tree of all the diversified forms of life which inhabit the earth.

  But the turn of the century also heralded the collapse of recapitulation. It died primarily because Mendelian genetics (rediscovered in 1900) rendered its premises untenable. (The “parade of adults” required that evolution proceed only by an addition of new stages to the end of ancestral ontogenies. But if new features are controlled by genes, and these genes must be present from the very moment of conception, then why shouldn’t new features be expressed at any stage of embryonic development or later growth?) But its luster had faded long before. The assumption that ancestral reminiscences could always be distinguished from recent embryonic adaptations had not been sustained. Too many stages were missing, too many others discombobulated. The application of Haeckel’s law produced endless, unresolvable, fruitless argument, not an unambiguous tree of life. Some tree builders wanted to derive vertebrates from echinoderms, others from annelid worms, still oth
ers from horseshoe crabs. E.B. Wilson, apostle of the “exact,” experimental method that would supplant speculative phylogenizing, complained in 1894:

  It is a ground of reproach to morphologists that their science should be burdened with such a mass of phylogenetic speculations and hypotheses, many of them mutually exclusive, in the absence of any well-defined standard of value by which to estimate their relative probability. The truth is that the search…has too often led to a wild speculation unworthy of the name of science; and it would be small wonder if the modern student, especially after a training in the methods of more exact sciences, should regard the whole phylogenetic aspect of morphology as a kind of speculative pedantry unworthy of serious attention.

  Phylogenizing fell from general favor, but you can’t keep an intrinsically exciting subject down. (I speak of high-level phylogenizing—the trunk and limbs. For twigs and small branches, where evidence is more adequate, work has always proceeded apace, with more assurance and less excitement.) We didn’t need “Roots” to remind us that genealogy exerts a strange fascination over people. If uncovering the traces of a distant great-grandparent in a small overseas village fills us with satisfaction, then probing further back to an African ape, a reptile, a fish, that still-unknown ancestor of vertebrates, a single-celled forebear, even to the origin of life itself, can be positively awesome. Unfortunately, one might even say perversely, the further back we go, the more fascinated we become and the less we know. In this column, I will discuss one classic issue in phylogenizing as an example of the joys and frustrations of a subject that will not go away: the origin of multicellularity in animals.