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The Dragons of Eden: Speculations on the Evolution of Human Intelligence

by Carl Sagan
Random House, 263 pp., $8.95

The intellectual landmines laid for us by Charles Darwin more than a century ago continue to explode. As each cloud of dust settles back around us, we begin to see a little more clearly the ways in which the history of humanity interlocks with and reflects the continued presence of patterns apparent in the history of nature. Yet each of these novel insights in turn finds itself resisted by those who have a major investment in the uniqueness of the human species, and who feel themselves threatened by any new analogies between the human species and other kinds of animals—most particularly, between the modes of life and experience of human beings (their psyche and ethos) and those of other primates and higher animals. At times, the passions aroused in the resulting controversies even remind us of the outburst that greeted the original publication of The Origin of Species in 1859: recall, for instance, last year’s angry exchanges in response to Edward Wilson’s book, Sociobiology.

From the standpoint of the development of ideas in the long term, however, these opponents seem to have been living in something of a fool’s paradise. When Darwin finally let The Descent of Man go to press in 1871—his argument in the Origin had been discreetly silent about the evolutionary status of human beings—he claimed explicitly only that “Man still bears in his bodily frame the indelible stamp of his lowly origin.” As a result, the first scientific and philosophical battles about human evolution were all fought out around the morphological features of different species, around fossil bones and brainpans, the beaks of finches and the necks of giraffes. And since the scientific case for the animal ancestry of the human species had been largely made out on morphological grounds, it seemed possible for a while to resist the further encroachment of evolutionary ideas by adopting a policy of containment. Evolution had to do, not with ethos or psyche, but with morphe alone. The mental and moral sciences could continue to hold themselves aloof from the natural sciences. Geist remained distinct from Natur. The methodological dualism which Kant had substituted for the ontological dualism of earlier Cartesian natural philosophy still seemed to protect human history from any danger of being engulfed in natural history.

This defense line was, at best, a temporary one. As early as 1838, Darwin himself had been thinking of ways in which his vision of man as part of a single creation with all other animals could be extended into psychology also. In private notebooks that remained unpublished in the Cambridge University Library until the 1970s1 he confessed himself a “materialist” in his views about the function of the human brain as the organ of higher mental activities. Yet he understood well enough how much damage would be done to the reception of his evolutionary theories by any public profession of these views: not least from memories of the storm provoked by William Lawrence’s Lectures on Physiology, Zoology and the Natural History of Man (1816-1819), which was still blowing strongly against the materialist position when Darwin was a medical student at Edinburgh University in 1825-1827.2 So it was only toward the end of his life that Darwin allowed himself to give some hints of his ideas about mental evolution and the psychic affinities between humanity and the other species: e.g., in his book, The Expression of the Emotions in Man and Animals (1872), a pioneering study in the comparative psychology of affect, which has been followed up only in our own day, and is still not generally appreciated at its true worth.

The task of putting human nature and affairs (psychosocial as well as physiological) into a single perspective with natural science and natural history has been a slow and painful one.3 The cosmologies and natural philosophies of classical antiquity and preclassical times saw the chronicle of human history as played out against a static backdrop of the natural world. Though Heraclitus might declare that everything was “in flux,” only the Epicureans took very seriously the problem of relating the flux of human affairs to that of Nature herself. On this issue, Platonists and Aristotelians were for once lined up on the same side, along with all those historical writers who followed Thucydides in seeing history as the record of human character or personality displaying its characteristic virtues and weaknesses within the unfolding of political and social events.

If most classical thinkers set Humanity over against Nature, this was of course even more clearly the case with the Christian story of the Fall and Redemption. Until 1700 or later, God’s Natural Creation was almost universally perceived as unchanging (at any rate within the present Divine Dispensation), and served as a fixed stage for human beings, who were alone directly and intimately involved in the historical drama of sin, grace, and salvation. So it is worth noting how much care was taken by those first few historically minded eighteenth-century speculators (e.g., Vico) for whom the origins of human society, customs, and feelings once again became a serious theoretical issue to rebut the charge that they were “Epicureans.”

Spokesmen for the conservative bien pensant position certainly knew who was the enemy, and how to blacken anyone who strayed in that direction. (More recently, this has been one of the issues that divided Hegel from Marx. For the historical idealists, the “historical dialectic” affected only Geist, as manifested in human history, while Natur was perceived as essentially repetitive, not progressive.) And, even today, it cannot be said that many “human scientists”—whether anthropologists or historians, political theorists or social philosophers—view Darwin’s longer term project for integrating our understanding of human nature with that of our fellow animals, in their mental and social as well as their somatic aspects, with any real relish or eagerness. Too often, the topic awakens in them only irritation or distaste. A good illustration of this is Marshall Sahlins’s polemical response to E.O. Wilson’s Sociobiology, which presses the argument for recognizing the uniqueness of the Geisteswissenschaften against Wilson with a certain weary impatience.4

Carl Sagan’s engaging and well written new book is an antidote to much of the recent controversy about human evolution. His style and manner have a certain briskness and astringency, an alkalinity perhaps, which come pleasantly to the reader after the acidity of last year’s narrower debate over Wilson. Sagan himself is best known as an aficionado of space travel, and as a man much preoccupied with the problem of establishing contact with any intelligent beings there may be in other planetary systems or galaxies; he was most recently in the public eye in connection with the Viking landings on Mars. But we find him here writing not about astronomy or interplanetary technology so much as about brain physiology and linguistics, evolution and psychology, dreaming and DNA. He does so not as a specialist in one field of science who has been tempted to wander out of his proper field and hazard amateur speculations about other scientists’ subject matter. Rather, the book shows that he is a true “natural philosopher,” whose concern with extraterrestrial intelligence is only one element in a larger scientific program, and whose real goal is to produce a revised version of the story of human history and destiny, within the boundary conditions set by the ideas of twentieth-century natural science.

His canvas is thus a broad one. In showing us the psychological significance of our evolutionary ancestry, he seeks to balance off the respective contributions to human intelligence and mental life of our genes and of our brains. Looking at the sweep of evolutionary history, he concludes that there was a “gradual increase through evolutionary time of both the amount of information contained in the genetic material and the amount of information contained in the brains of organisms”; but as time went on reptilian creatures evolved which for the first time had more information capacity in their brains than in their genes. Since these early creatures—probably a few hundred million years ago—there have been two major bursts of brain evolution, involving the development of the limbic system and of the neocortex, and associated with the emergence of mammals and the advent of manlike primates. As a result, we inherit a “triune” brain whose threefold structure and modes of functioning (reflected in the metapsychologies of Western thinkers from Plato to Freud) need to be related to their evolutionary history. Only if we understand the manner in which the human brain has come to its present form, Sagan argues, can we speculate at all fruitfully about the directions in which human intelligence and its bodily agencies are capable of evolving further in the future.

The particular problems on which Carl Sagan rightly chooses to focus his discussion have to do with the evolution of the brain and its function as the organ of human feelings, experience, and intelligence. Like many other modern observers, he is struck by the evolutionary “modernity” of the neocortex, and by the complex ways in which its operations monitor, yet are constrained by, the operations of parts of the brain that are more deeply seated and “older” as far as evolution is concerned. Where some recent popular writers, such as Arthur Koestler, have treated the limbic system and other deeper structures as having crudely emotional functions, over which the somewhat frail neocortex has only marginal rational control, Sagan gives us a more subtle and historically informed view.

Those of our evolutionary ancestors that had not yet developed any major cortical systems, he argues, were adapted to alternative modes of life, from which many of our own intelligent, and essentially linguistic, operations were absent. But they did not lack control and monitoring mechanisms of their own kinds, adequate to their proper modes of existence. Moreover, to the extent that the deeper structures of our modern brains still embody the mechanisms that were formed in the crucible of that earlier existence, we too can still—in sleep, in dreams, perhaps even in the echoes awakened by our myths—get back in touch with that earlier mode of life.

The “dragons” of Sagan’s title refer to the scaly winged creatures halfway between the dinosaurs and the birds that may have been the chief predators against which those earlier brain formations were our ancestors’ prime defenses. The collective memory of those far off but crucial days in a geological “Eden” may still, Sagan hints—and not entirely in a spirit of whimsy—be preserved in the widespread occurrence of legends about such dragons.

This discussion of brain structure, both as a product of earlier evolution and as the instrumentality of human intelligence, is only the center piece of Sagan’s larger picture of world history. Writing in the tradition of Buffon’s Epoques de la Nature (1778), he begins with an over-all account of the “cosmic calendar,” as natural scientists now conceive it. Where Buffon chose to map the successive phases in the history of the earth against the traditional Days of Creation, Sagan invites us to see cosmic history against the time scale of a single year. By that measure, he tells us, life began on earth only around “September 25,” while the human species made its appearance around 10:30 PM on “December 31”—recorded history being represented by the last ten seconds alone. Presenting the vast abysms of unrecorded time in this kind of way can be irritating to humanists, since it may appear intended as a kind of clever putdown. In Sagan’s hands the impression is different. At its best, his writing has the same appealing style as that of Loren Eiseley, and the humanity of his motives is never in question.

Indeed, by the end of the book his deeper project becomes clear: namely that in the long run—in the cosmic long run, that is—the human species will have to reach out to the other intelligent beings that presumably occupy their own distant corners of the cosmos, and make itself part of a larger cooperative alliance of intelligent creatures. (Recall how Buffon, too, speculated about the living creatures which—he presumed—occupied the other planets and satellites of the solar system.) So Sagan’s quest for ways of communicating with extraterrestrial beings ceases to appear a mere technological fantasy, and reveals itself for what it is: the pursuit of a “wider union” between humanity and its fellow inhabitants of this and other galaxies, to serve as the turning point by which human or terrestrial history can be finally embedded into, and integrated with, cosmic natural history.

Quite aside from all questions about the merits of Sagan’s conclusions, to which I shall return, it is good to see this kind of book being written at all. Over the last fifteen years, most public discussion of science and scientific ideas has been narrowly restricted to questions about the technological “fruit” of scientific advances; and the enterprise of science itself has as a result been made a whipping boy by critics whose attention would have been better paid to the sins of industrial monopolies and the feebleness of America’s system of government. So it is more than time for us to be reminded that the central concerns of much modern science have been cosmological, and that through most of its three-hundred-year history science has been associated far more closely with theology than with technology.

Natural philosophy has at all times been the product not of greed but of wonder. Its underlying appetite has been one not for more and cheaper consumer goods, but for a more comprehensive and comprehensible vision of Humanity and its place in Nature. (Thomas Henry Huxley’s more euphonious phrase—Man’s Place in Nature—has of course been overtaken by events.) In his attempt at a synthesis of all the sciences that can throw light on our origins and prehistoric evolution, from the first mammals of the Triassic period through the primates and early hominids to the human species as we know it, Sagan is accordingly writing in an ancient and distinguished tradition.

The “decentering” from local, human concerns that is required, if we are to follow Sagan into these speculations, will not come easily to many people. For much humanist thought about our affairs takes a basic position toward history and society that is, by Sagan’s standards, entirely parochial. Its locus of attention is terrestrial; its historical span of attention is limited to a few decades—can we make it through the half century to the year 2027?—and it continues to set human life and affairs apart from those of other species and beings. Whether to practical people who are preoccupied with oil prices, population pressure, and the balance of power, or to humanist intellectuals—Leavis or Lévi-Strauss, Marshall Sahlins or Robert Heilbroner—the suggestion that we should put this secular, planetary, species-directed parochialism aside in favor of a more comprehensive astronomical/historical perspective may seem frivolous and misdirected.

Yet our view of things will surely remain only partial unless we are prepared, and able, to view our affairs in that larger perspective also. It is, after all, not so long since “realists” were resisting the argument that human affairs need to be considered and analyzed as global or continental problems, instead of being dealt with only as concerning individual nations, city-states, or local communities. We should surely be ready to entertain all reasonable and scientifically justifiable thoughts about the place in nature, not merely of man or humanity, but also of the earth, of our sun, and ultimately of the entire galaxy.

This clash of perspectives between cosmologists and humanists is, of course, an old story, which goes back at least as far as classical Athens. Though ridiculed by Aristophanes for his supposedly excessive interest in astronomical matters, Socrates himself in fact abandoned the pre-Socratic philosophers’ tradition of cosmological speculation, and refocused the philosophical debate on human problems and values. In very much the same spirit, Michel de Montaigne laid one of the foundation stones of modern humanism when he dismissed as presumptuous all attempts to make rational sense of astrophysics. Instead, Montaigne placed at the center of his position a motto which is often quoted as a sign of his liberality, but was in truth intended as a restriction on human inquiry—Nihil humanum a me alienum puto—“I deem nothing foreign to me, so long as it has to do with human affairs.” And those of our contemporaries who have committed themselves to matters of human welfare and relevance, at all costs, will probably share the irritation that Sagan’s continued devotion to historical cosmology would have provoked in Montaigne.

By contrast, those who have immersed themselves in the cosmological debate, as it has developed from Thales and Anaximander up to Hoyle, Wheeler, and Sagan, are able to lift their eyes from the human perplexities of the 1970s, to contemplate the larger world from different points of view, and to measure its affairs against very different scales both of time and of space. They not only “have the future in their bones”—to quote c.p. Snow—they have the remote past and the most distant parts of the universe at their fingertips also. Having a sense of the boundary conditions that our cosmic situation imposes on the development of human affairs may not, of course, contribute much to the making of policy, or the determination of short-term attitudes; and to that extent the wording of Snow’s phrase is perhaps too portentous. Yet this, too, should be one element in the formation of a genuinely “humane” view of human affairs; and one important virtue of a book like Carl Sagan’s is the contribution it makes toward reconciling the parochially human and the cosmological perspectives.

To say this is not to accept Sagan’s argument entirely as it stands. In certain respects his background in the physical sciences betrays him, and he misses some important biological tricks. For instance, he has apparently fallen too completely for the molecular biologists’ propaganda view of genetics as a mere sub-branch of biochemistry, in speaking of human beings as

to a remarkable degree, the results of the interactions of an extremely complex array of molecules.

In spite of his insistence on keeping the genes and the brain in balance, he does not do full justice to the point he cites from Sherwood Washburn—that

Much of what we think of as human evolved long after the use of tools. It is probably more correct to think of much of our structure as the result of culture than it is to think of men anatomically like ourselves slowly developing culture.

For what is true about our anatomical structure on the gross scale goes equally for our structure on the subcelluar level. In some respects, our “genes” are what they are as the outcome of evolutionary changes that involved crucial cultural elements.

The point goes beyond Sagan’s argument to the whole debate about socio-biology and related topics. For instance, E.O. Wilson’s explanation of the continuities between human social organization and the patterns of collaboration found in other social species links social theory to “genetics,” but only in the sense of population genetics. And, as Wilson himself concedes, the relations between population genetics and biochemical genetics are speculative. Since evolutionary selection acts always on the “phenotype”—i.e., the fully developed, self-reproducing form—rather than directly on the “genotype”—e.g., the subcellular system of nucleic acids—the effects of cultural differences on the relative survival of different social populations (whether human or animal) may quickly become so great as to equal, or even in some cases swamp, the effects of biochemical differences. It is tool-using, language-using, culture-transmitting populations that are being preferentially selected; and the superiority of one set of tools, one repertory of language, one mode of culture over others is consequently capable of making a crucial difference to the survival of populations, even from the stand-point of genetics.

Wilson himself has sometimes talked as though a human being were simply “the gene’s way of making another gene”—i.e., as though the survival of the “gene pool” were the controlling factor in all social evolution—and Sagan’s argument is at times open to the same interpretation. I would note here, simply, that “gene pools” are not the only entities that exploit individuals in the interest of their own survival. Institutions and sociocultural forms do the same. The devout believer is the Church’s way of ensuring the survival of the Church; the loyal citizen is the State’s way of ensuring the survival of the State; the scientific apprentice is physics’ way of ensuring the survival of physics; and so on. Once we reach the level of considering the genetics of social and cultural populations, such as those of the human species, we thus have to recognize that the “phenotype” on which evolution operates is itself made up of social and cultural, quite as much as of morphological, elements. So we are obliged neither to oppose culture and nature with Marshall Sahlins, nor to reduce culture to nature with Edward Wilson. Rather, we can now see that, even from a biological point of view, culture has the power to impose itself on nature from within.

There are a few other minor issues over which Sagan might be faulted. For example: he cites Chomsky’s speculations about universal grammar in support of the idea that the human brain was evolutionally preadapted for language. Yet he should have noted that Chomsky himself has always been very scornful of all attempts to discuss the evolutionary history of language, or the physiological preconditions for its use. It is not in the theoretical linguistics of the MIT group but rather in the work of aphasiologists and clinical neurologists that he should have sought the evidence he wanted of the connections between the character of human language and the detailed anatomy of the brain.5 Toward the end of the book, again, the excursions Sagan makes into such current issues as the ethics of abortion and the definition of death will strike some readers as thin, irrelevant, and even a little stale. (A tough-minded editor would have blue-penciled them.)

One may find it necessary to take issue with Carl Sagan over many details, but the over-all force of his argument will survive a great deal of correction of the details. It is a pleasure to have someone writing about scientific cosmology once again so elegantly, intelligently, and with such literary flair, after the comparative drought of the last twenty years.

  1. 1

    These “M” and “N” Notebooks have been admirably transcribed and edited by Paul H. Barrett of Michigan State University and published with commentaries and a long introductory essay by Howard E. Gruber of Rutgers, in the book Darwin on Man (Dutton, 1974).

  2. 2

    Gruber and Barrett record a curious incident at Edinburgh in March 1827, which shows how violent the feelings on this topic still were: op. cit., pp. 39, 479-480.

  3. 3

    The obstacles to this task, failing a realistic sense of the vast extension of cosmic time, are one of the chief topics discussed in my own examination of the stages by which natural history and human history gradually negotiated some kind of a common framework and timescale, in The Discovery of Time (Harper and Row, 1965).

  4. 4

    See The Use and Abuse of Biology (University of Michigan Press, 1976).

  5. 5

    See, for instance, the admirable papers of Norman Geschwind, collected in the volume Selected Papers on Language and the Brain (D. Reidel Publishing Co., 1974), especially the 1964 essay on “The Development of the Brain and the Evolution of Language.”

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