In reality, the story is not so simple. The preformationists were as careful and accurate in their empirical observations as the epigeneticist. Moreover, if heroes we must have, that honor might as well fall to the preformationists who upheld, against the epigeneticists, a view of science quite congenial with our own.
The imagination of a few peripheral figures must not be taken as the belief of an entire school. The great preformationists—Malpighi, Bonnet, and von Haller,—all knew perfectly well that the chick embryo seemed to begin as a simple tube and become more and more complex as organs differentiated within the egg. They had studied and drawn the embryology of the chick in a series of astute observations that matched anything achieved by contemporary epigeneticists.
Preformationists and epigeneticists did not disagree about their observations; but, whereas epigeneticists were prepared to take those observations literally, the preformationists insisted on probing “behind appearance.” They claimed that the visual manifestations of development were deceptive. The early embryo is so tiny, so gelatinous, and so transparent that the preformed structures could not be discerned by the crude microscopes then available. Bonnet wrote in 1762: “Do not mark the time when organized beings begin to exist by the time when they begin to become visible; and do not constrain nature by the strict limits of our senses and instruments.” Moreover, the preformationists never believed that preformed structures were organized into a perfect miniature homunculus in the egg itself. The rudiments existed in the egg to be sure, but in relative positions and proportions bearing little relationship to adult morphology. Again, Bonnet in 1762: “While the chick is still a germ, all its parts have forms, proportions and positions which differ greatly from those that they will attain during development. If we were able to see the germ enlarged, as it is when small, it would be impossible for us to recognize it as a chick. All the parts of the germ do not develop at the same time and uniformly.”
But how did the preformationists explain the reductio ad absurdum of encasement—the encapsulation of our entire history in the ovaries of Eve? Very simply—this concept was not absurd in an eighteenth-century context.
First of all, scientists believed that the world had existed—and would endure—for only a few thousand years. One had, therefore, to encapsulate only a limited number of generations, not the potential products of several million years on a twentieth-century geological time chart.
Secondly, the eighteenth century had no cell theory to set a lower boundary to organic size. It now seems absurd to postulate a fully formed homunculus smaller than the minimum size of a single cell. But an eighteenth-century scientist had no reason to postulate a lower limit to size. In fact, it was widely believed that Leeuwenhoek’s animalcules, the single-celled microscopic creatures that had so aroused the imagination of Europe, had complete sets of miniature organs. Thus Bonnet, supporting the corpuscular theory (that light is made of discrete particles), rhapsodized about the inconceivable tininess of the several million globules of light that penetrate all at once into the supposed eyes of animalcules. “Nature works as small as it wishes. We know not at all the lower boundary of the division of matter, but we see that it has been prodigiously divided. From the elephant to the mite, from the whale to the animalcule 27 million times smaller than the mite, from the globe of the sun to the globule of light, what an inconceivable multitude of intermediate degrees!”
Why did the preformationists feel such a need to penetrate behind appearances? Why would they not accept the direct evidence of their senses? Consider the alternatives. Either the parts are present from the first or the fertilized egg is utterly formless. If the egg is formless, then some external force must unerringly impose a design upon matter only potentially capable of producing it. But what kind of a force could this be? And must there be a different force for each species of animal? How can we learn about it, test it, perceive it, touch it, or understand it? How could it represent any more than an insubstantial appeal to a mysterious and mystical vitalism?
Preformationism represented the best of Newtonian science. It was designed to save a general attitude, which we would recognize today as “scientific,” from a vitalism that the evidence of raw sensation implied. If the egg were truly unorganized, homogeneous material without preformed parts, then how could it yield such wondrous complexity without a mysterious directing force? It does so, and can do so, only because the structure (not merely the raw material) needed to build this complexity already resides in the egg. In this light, Bonnet’s statement about the triumph of reason over the senses seems itself more reasonable.
Finally, who can say that our current understanding of embryology marks the triumph of epigenesis? Most great debates are resolved at Aristotle’s golden mean, and this is no exception. From our perspective today, the epigeneticists were right; organs differentiate sequentially from simpler rudiments during embryological development; there are no preformed parts. But the preformationists were also right in insisting that complexity cannot arise from formless raw material—that there must be something within the egg to regulate its development. All we can say (as if it mattered) is that they incorrectly identified this “something” as preformed parts, where we now understand it as encoded instructions built of DNA. But what else could we expect from eighteenth-century scientists, who knew nothing of the player piano, not to mention the computer program? The idea of a coded program was not part of their intellectual equipment.
And, come to think of it, what could be more fantastic than the claim that an egg contains thousands of instructions, written on molecules that tell the cell to turn on and off the production of certain substances that regulate the speed of chemical processes? The notion of preformed parts sounds far less contrived to me. The only thing going for coded instructions is that they seem to be there.
26 | Posture Maketh the Man
NO EVENT DID MORE to establish the fame and prestige of The American Museum of Natural History than the Gobi Desert expeditions of the 1920s. The discoveries, including the first dinosaur eggs, were exciting and abundant, and the sheer romance fit Hollywood’s most heroic mold. It is still hard to find a better adventure story than Roy Chapman Andrews’s book (with its chauvinistic title): The New Conquest of Central Asia. Nonetheless, the expeditions utterly failed to achieve their stated purpose: to find in Central Asia the ancestors of man. And they failed for the most elementary of reasons—we evolved in Africa, as Darwin had surmised fifty years earlier.
Our African ancestors (or at least our nearest cousins) were discovered in cave deposits during the 1920s. But these australopithecines failed to fit preconceived notions of what a “missing link” should look like, and many scientists refused to accept them as bona fide members of our lineage. Most anthropologists had imagined a fairly harmonious transformation from ape to human, propelled by increasing intelligence. A missing link should be intermediate in both body and brain—Alley Oop or the old (and false) representations of stoopshouldered Neanderthals. But the australopithecines refused to conform. To be sure, their brains were bigger than those of any ape with comparable body size, but not much bigger (see essays 22 and 23). Most of our evolutionary increase in brain size occurred after we reached the australopithecine level. Yet these smallbrained australopithecines walked as erect as you or I. How could this be? If our evolution was propelled by an enlarging brain, how could upright posture—another “hallmark of hominization,” not just an incidental feature—originate first? In a 1963 essay, George Gaylord Simpson used this dilemma to illustrate
the sometimes spectacular failure to predict discoveries even when there is a sound basis for such prediction. An evolutionary example is the failure to predict discovery of a “missing link,” now known [Australopithecus], that was upright and tool-making but had the physiognomy and cranial capacity of an ape.
We must ascribe this “spectacular failure” primarily to a subtle prejudice that led to the following, invalid extrapolation: We dominate other anima
ls by brain power (and little else); therefore, an increasing brain must have propelled our own evolution at all stages. The tradition for subordinating upright posture to an enlarging brain can be traced throughout the history of anthropology. Karl Ernst von Baer, the greatest embryologist of the nineteenth century (and second only to Darwin in my personal pantheon of scientific heroes) wrote in 1828: “Upright posture is only the consequence of the higher development of the brain … all differences between men and other animals depend upon construction of the brain.” One hundred years later, the English anthropologist G. E. Smith wrote: “It was not the adoption of the erect attitude or the invention of articulate language that made man from an ape, but the gradual perfecting of a brain and the slow building of the mental structure, of which erectness of carriage and speech are some of the incidental manifestations.”
Against this chorus of emphasis upon the brain, a very few scientists upheld the primacy of upright posture. Sigmund Freud based much of his highly idiosyncratic theory for the origin of civilization upon it. Beginning in his letters to Wilhelm Fliess in the 1890s and culminating in his 1930 essay on Civilization and Its Discontents, Freud argued that our assumption of upright posture had reoriented our primary sensation from smell to vision. This devaluation of olfaction shifted the object of sexual stimulation in males from cyclic odors of estrus to the continual visibility of female genitalia. Continual desire of males led to the evolution of continual receptivity in females. Most mammals copulate only around periods of ovulation; humans are sexually active at all times (a favorite theme of writers on sexuality). Continual sexuality has cemented the human family and made civilization possible; animals with strongly cyclic copulation have no strong impetus for stable family structure. “The fateful process of civilization,” Freud concludes, “would thus have set in with man’s adoption of an erect posture.”
Although Freud’s ideas gained no following among anthropologists, another minor tradition did arise to stress the primacy of upright posture. (It is, by the way, the argument we tend to accept today in explaining the morphology of australopithecines and the path of human evolution.) The brain cannot begin to increase in a vacuum. A primary impetus must be provided by an altered mode of life that would place a strong, selective premium upon intelligence. Upright posture frees the hands from locomotion and for manipulation (literally, from manus = “hand”). For the first time, tools and weapons can be fashioned and used with ease. Increased intelligence is largely a response to the enormous potential inherent in free hands for manufacture—again, literally. (Needless to say, no anthropologist has ever been so naïve as to argue that brain and posture are completely independent in evolution, that one reached its fully human status before the other began to change at all. We are dealing with interaction and mutual reinforcement. Nevertheless, our early evolution did involve a more rapid change in posture than in brain size; complete freeing of our hands for using tools preceded most of the evolutionary enlargement of our brain).
In another proof that sobriety does not make right, von Baer’s mystical and oracular colleague Lorenz Oken hit upon the “correct” argument in 1809, while von Baer was led astray a few years later. “Man by the upright walk obtains his character,” writes Oken, “the hands become free and can achieve all other offices.… With the freedom of the body has been granted also the freedom of the mind.” But the champion of upright posture during the nineteenth century was Darwin’s German bulldog Ernst Haeckel. Without a scrap of direct evidence, Haeckel reconstructed our ancestor and even gave it a scientific name, Pithecanthropus alalus, the upright, speechless, small-brained ape-man. (Pithecanthropus, by the way, is probably the only scientific name ever given to an animal before it was discovered. When Du Bois discovered Java Man in the 1890s, he adopted Haeckel’s generic name but he gave it the new specific designation Pithecanthropus erectus. We now usually include this creature in our own genus as Homo erectus.)
But why, despite Oken and Haeckel’s demurral, did the idea of cerebral primary become so strongly entrenched? One thing is sure; it had nothing to do with direct evidence—for there was none for any position. With the exception of Neanderthal (a geographic variant of our own species according to most anthropologists), no fossil humans were discovered until the closing years of the nineteenth century, long after the dogma of cerebral primary was established. But debates based on no evidence are among the most revealing in the history of science, for in the absence of factual constraints, the cultural biases that affect all thought (and which scientists try so assiduously to deny) lie nakedly exposed.
Indeed, the nineteenth century produced a brilliant exposé from a source that will no doubt surprise most readers—Friedrich Engels. (A bit of reflection should diminish surprise. Engels had a keen interest in the natural sciences and sought to base his general philosophy of dialectical materialism upon a “positive” foundation. He did not live to complete his “dialectics of nature,” but he included long commentaries on science in such treatises as the Anti-Dühring.) In 1876, Engels wrote an essay entitled, The Part Played by Labor in the Transition from Ape to Man. It was published posthumously in 1896 and, unfortunately, had no visible impact upon Western science.
Engels considers three essential features of human evolution: speech, a large brain, and upright posture. He argues that the first step must have been a descent from the trees with subsequent evolution to upright posture by our ground-dwelling ancestors. “These apes when moving on level ground began to drop the habit of using their hands and to adopt a more and more erect gait. This was the decisive step in the transition from ape to man.” Upright posture freed the hand for using tools (labor, in Engels’s terminology); increased intelligence and speech came later.
Thus the hand is not only the organ of labor, it is also the product of labor. Only by labor, by adaptation to ever new operations … by the ever-renewed employment of these inherited improvements in new, more and more complicated operations, has the human hand attained the high degree of perfection that has enabled it to conjure into being the pictures of Raphael, the statues of Thorwaldsen, the music of Paganini.
Engels presents his conclusions as though they followed deductively from the premises of his materialist philosophy, but I am confident that he cribbed them from Haeckel. The two formulations are almost identical, and Engels cites the relevant pages of Haeckel’s work for other purposes in an earlier essay written in 1874. But no matter. The importance of Engels’s essay lies, not in its substantive conclusions, but in its trenchant political analysis of why Western science was so hung up on the a priori assertion of cerebral primacy.
As humans learned to master their material surroundings, Engels argues, other skills were added to primitive hunting—agriculture, spinning, pottery, navigation, arts and sciences, law and politics, and finally, “the fantastic reflection of human things in the human mind: religion.” As wealth accumulated, small groups of men seized power and forced others to work for them. Labor, the source of all wealth and the primary impetus for human evolution, assumed the same low status of those who labored for the rulers. Since rulers governed by their will (that is, by feats of mind), actions of the brain appeared to have a motive power of their own. The profession of philosophy followed no unsullied ideal of truth. Philosophers relied on state or religious patronage. Even if Plato did not consciously conspire to bolster the privileges of rulers with a supposedly abstract philosophy, his own class position encouraged an emphasis on thought as primary, dominating, and altogether more noble and important than the labor it supervised. This idealistic tradition dominated philosophy right through to Darwin’s day. Its influence was so subtle and pervasive that even scientific, but apolitical, materialists like Darwin fell under its sway. A bias must be recognized before it can be challenged. Cerebral primacy seemed so obvious and natural that it was accepted as given, rather than recognized as a deep-seated social prejudice related to the class position of professional thinkers and their patrons. Engels writ
es:
All merit for the swift advance of civilization was ascribed to the mind, to the development and activity of the brain. Men became accustomed to explain their actions from their thoughts, instead of from their needs.… And so there arose in the course of time that idealistic outlook on the world which, especially since the downfall of the ancient world, has dominated men’s minds. It still rules them to such a degree that even the most materialistic natural scientists of the Darwinian school are still unable to form any clear idea of the origin of man, because under that ideological influence they do not recognize the part that has been played therein by labor.
The importance of Engels’s essay does not lie in the happy result that Australopithecus confirmed a specific theory proposed by him—via Haeckel—but rather in his perceptive analysis of the political role of science and of the social biases that must affect all thought.
Indeed, Engels’s theme of the separation of head and hand has done much to set and limit the course of science throughout history. Academic science, in particular, has been constrained by an ideal of “pure” research, which in former days barred a scientist from extensive experimentation and empirical testing. Ancient Greek science labored under the restriction that patrician thinkers could not perform the manual work of plebeian artisans. Medieval barber-surgeons who had to deal with battlefield casualties did more to advance the practice of medicine than academic physicians who rarely examined patients and who based their treatment on a knowledge of Galen and other learned texts. Even today, “pure” researchers tend to disparage the practical, and terms such as “aggie school” and “cow college” are heard with distressing frequency in academic circles. If we took Engels’s message to heart and recognized our belief in the inherent superiority of pure research for what it is—namely social prejudice—then we might forge among scientists the union between theory and practice that a world teetering dangerously near the brink so desperately needs.
Ever Since Darwin: Reflections in Natural History Page 18