(The Dragons of Eden, Carl Sagan, 1986 AD)

From experiments such as those with squirrel monkeys, MacLean has developed a captivating model of brain structure and evolution that he calls the triune brain. "We are obliged," he says, "to look at ourselves and the world through the eyes of three quite different mentalities," two of which lack the power of speech. The human brain, MacLean holds, "amounts to three interconnected biological computers," each with "its own special intelligence, its own subjectivity, its own sense of time and space, its own memory, motor, and other functions." Each brain corresponds to a separate major evolutionary step. The three brains are said to be distinguished neuroanatomically and functionally, and contain strikingly different distributions of the neurochemicals dopamine and cholinesterase.

At the most ancient part of the human brain lies the spinal cord; the medulla and pons, which comprise the hindbrain; and the midbrain. This combination of spinal cord, hindbrain and midbrain MacLean calls the neural chassis. It contains the basic neural machinery for reproduction and self-preservation, including regulation of the heart, blood circulation and respiration. In a fish or an amphibian it is almost all the brain there is. But a reptile or higher animal deprived of its forebrain is, according to MacLean, "as motionless and aimless as an idling vehicle without a driver."

Indeed, grand mal epilepsy can, I think, be described as a disease in which the cognitive drivers are all turned off because of a kind of electrical storm in the brain, and the victim is left momentarily with nothing operative but his neural chassis. This is a profound

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impairment, temporarily regressing the victim back several hundreds of millions of years. The ancient Greeks, whose name for the disease we still use, recog-nized its profound character and called it the disease inflicted by the gods.

MacLean has distinguished three sorts of drivers of the neural chassis. The most ancient of them surrounds the midbrain (and is made up mostly of what ncuroanatomists call the olfactostriatum, the corpus striatum, and the globus pallidus). We share it with the other mammals and the reptiles. It probably evolved several hundred million years ago. MacLean calls it the reptilian or R-complex. Surrounding the R-complex is the limbic system, so called because it borders on the underlying brain. (Our arms and legs are called limbs because they are peripheral to the rest of the body.) We share the limbic system with the other mammals but not, in its full elaboration, with the reptiles. It probably evolved more than one hun-dred and fifty million years ago. Finally, surmounting the rest of the brain, and clearly the most recent evo-lutionary accretion, is the neocortex. Like the higher mammals and the other primates, humans have a rel-atively massive neocortex. It becomes progressively more developed in the more advanced mammals. The most elaborately developed neocortex is ours (and the dolphins' and whales') . It probably evolved several tens of millions of years ago, but its development accelerated greatly a few million years ago when hu-mans emerged. A schematic representation of this picture of the human brain is shown opposite, and a comparison of the limbic system with the neocortex in three contemporary mammals is shown above. The concept of the triune brain is in remarkable accord with the conclusions, drawn independently from studies of brain to body mass ratios in the previous chapter, that the emergence of mammals and of primates (especially humans) was accompanied by major bursts in brain evolution.

The Brain and the Chariot59

The reason for recapitulation may be understood as follows: Natural selection operates only on individuals, not on species and not very much on eggs or fetuses. Thus the latest evolutionary change appears postpar-tum. The fetus may have characteristics, like the gill slits in mammals, that are entirely maladaptive after birth, but as long as they cause no serious problems for the fetus and are lost before birth, they can be re-tained. Our gill slits are vestiges not of ancient fish but of ancient fish embryos. Many new organ systems

Schematic views from the top and from the side of the rabbit, cat, and monkey brains. The dark stippled area is the limbic system, seen most easily in the side views. The white furrowed regions represent the neocortex, visible most readily in the top views.

A photograph taken with an electron microscope of a small plant called a red alga. Its scientific name is Porphyridium cruentum. The chioroplast, this organism's photosynthetic factory, almost fills the entire cell. The photograph is mag-nified 23,000 times and was taken by Dr. Elizabeth Gantt of the Smithsonian Institution's Radiation Biology Labora-tory.

develop not by the addition and preservation but by the modification of older systems, as, for example, the modification of fins to legs, and legs to flippers or wings; or feet to hands to feet; or sebaceous glands to mammary glands; or gill arches to ear bones; or shark scales to shark teeth. Thus evolution by addition and the functional preservation of the preexisting struc-ture must occur for one of two reasons—either the old function is required as well as the new one, or there is no way of bypassing the old system that is consistent with survival.

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There are many other examples in nature of this sort of evolutionary development. To take an almost ran-dom case, consider why plants are green. Green-plant photosynthesis utilizes light in the red and the violet parts of the solar spectrum to break down water, build up carbohydrates and do other planty things. But the sun gives off more light in the yellow and the green part of the spectrum than in the red or violet. Plants with chlorophyll as their only photosynthetic pigment are rejecting light where it is most plentiful. Many plants seem belatedly to have "noticed" this and have made appropriate adaptations. Other pigments, which reflect red light and absorb yellow and green light, such as carotenoids and phycobilins, have evolved. Well and good. But have those plants with new photo-synthetic pigments abandoned chlorophyll? They have not. The figure on page 61 shows the photosynthetic factory of a red alga. The striations contain the chloro-phyll, and the little spheres nestling against these striations contain the phycobilins, which make a red alga red. Conservatively, these plants pass along the energy they acquire from green and yellow sunlight to the chlorophyll pigment that, even though it has not absorbed the light, is still instrumental in bridging the gap between light and chemistry in all plant photo-synthesis. Nature could not rip out the chlorophyll and replace it with better pigments; the chlorophyll is woven too deeply into the fabric of life. Plants with accessory pigments are surely. different. They are more efficient. But there, still working, although with dimin-ished responsibilities, at the core of the photosynthetic process is chlorophyll. The evolution of the brain has, I think, proceeded analogously. The deep and ancient parts are functioning still.

1 THE R-COMPLEX

If the preceding view is correct, we should expect the R-complex in the human brain to be in some sense

The Brain and the Chariot 63

performing dinosaur functions still; and the limbic cortex to be thinking the thoughts of pumas and ground sloths. Without a doubt, each new step in brain evolution is accompanied by changes in the physiology of the preexisting components of the brain. The evolution of the R-complex must have seen changes in the midbrain, and so on. What is more, we know that the control of many functions is shared in different components of the brain. But at the same time it would be astonishing if the brain components beneath the neocortex were not to a significant extent still performing as they did in our remote ancestors.

MacLean has shown that the R-complex plays an important role in aggressive behavior, territoriality, ritual and the establishment of social hierarchies. De-spite occasional welcome exceptions, this seems to me to characterize a great deal of modern human bureau-cratic and political behavior. I do not mean that the neocortex is not functioning at all in an American political convention or a meeting of the Supreme Soviet; after all, a great deal of the communication at such rituals is verbal and therefore neocortical. But it is striking how much of our actual behavior—as distinguished from what we say and think about it— can be described in reptilian terms. We speak com-monly of a "cold-blooded" killer. Machiavelli's advice to his Prince was "knowingly to adopt the beast."

In an interesting partial anticipation of these ideas, the American philosopher Susanne Langer wrote: "Human life is shot through and through with ritual, as it is also with animalian practices. It is an intricate fabric of reason and rite, of knowledge and religion, prose and poetry, fact and dream. . . . Ritual, like art, is essentially the active termination of a symbolic trans-formation of experience. It is born in the cortex, not in the 'old brain'; but it is born of an elementary need of that organ, once the organ has grown to human estate." Except for the fact that the R-complex is in the "old brain," this seems to be right on target.

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I want to be very clear about the social implications of the contention that reptilian brains influence human actions. If bureaucratic behavior is controlled at its core by the R-complex, does this mean there is no hope for the human future? In human beings, the neo-cortex represents about 85 percent of the brain, which is surely some index of its importance compared to the brainstem, R-complex and limbic system. Neuro-anatomy, political history, and introspection all offer evidence that human beings are quite capable of resisting the urge to surrender to every impulse of the reptilian brain. There is no way, for example, in which the Bill of Rights of the U.S. Constitution could have been recorded, much less conceived, by the R-complex. It is precisely our plasticity, our long childhood, that prevents a slavish adherence to genetically preprogrammed behavior in human beings more than in any other species. But if the triune brain is an accurate model of how human beings function, it does no good whatever to ignore the reptilian component of human nature, particularly our ritualistic and hierarthical behavior; On the contrary, the model may help us to understand what human beings are about. (I wonder, for example, whether the ritual aspects of many psychotic illnesses—e.g., hebephrenic schizophrenia—could be the result of hyperactivity of some center in the R-complex, or of a failure of some neocortical site whose function is to repress or override the R-complex. I also wonder whether the frequent ritualistic behavior in young children is a consequence of the still- incomplete development of their neocortices.)

In a curiously apt passage, G. K. Chesterton wrote: "You can free things from alien or accidental laws,

Opposite: Two photographs taken with an electron micro-scope within the third ventricle of the brain by Richard Steger of Wayne State University. Tiny waving hairs or cilia can be seen transporting small spherical brain proteins—like a crowd passing large beach balls overhead.

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but not from the laws of their own nature. . . . Do not go about . . . encouraging triangles to break out of the prison of their three sides. If a triangle breaks out of its three sides, its life comes to a lamentable end." But not all triangles are equilateral. Some sub-stantial adjustment of the relative role of each compo-nent of the triune brain is well within our powers.

2 THE LIMBIC SYSTEM

The limbic system appears to generate strong or par-ticularly vivid emotions. This immediately suggests an additional perspective on the reptilian mind: it is not characterized by powerful passions and wrenching contradictions but rather by a dutiful and stolid acqui-escence to whatever behavior its genes and brains dic-tate.

Electrical discharges in the limbic system sometimes result in symptoms similar to those of psychoses or those produced by psychedelic or hallucinogenic drugs. In fact, the sites of action of many psychotropic drugs are in the limbic system. Perhaps it controls exhilara-tion and awe and a variety of subtle emotions that we sometimes think of as uniquely human.

The "master gland," the pituitary, which influences other glands and dominates the human endocrine sys-tem, is an intimate part of the limbic region. The mood-altering qualities of endocrine imbalances give us an important hint about the connection of the lim-bic system with states of mind. There is a small almond-shaped inclusion in the limbic system called the amygdala which is deeply involved in both aggres-sion and fear. Electrical stimulation of the amygdala in placid domestic animals can rouse them to almost unbelievable states of fear or frenzy. In one case, a house cat cowered in terror when presented with a small white mouse. On the other hand, naturally ferocious animals, such as the lynx, become docile and tolerate being petted and handled when their amyg-dalas are extirpated. Malfunctions in the limbic sys-

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tern can produce rage, fear or sentimentality that have no apparent cause. Natural hyperstimulation may pro-duce the same results: those suffering from such a malady find their feelings inexplicable and inappro-priate; they may be considered mad.

At least some of the emotion-determining role of such limbic endocrine systems as the pituitary amyg-dala, and hypothalamus is provided by small hormonal proteins which they exude, and which affect other areas of the brain. Perhaps the best-known is the pituitary protein, . ACTH (adrenocorticotropic hor-mone), which can affect such diverse mental func-tions as visual retention, anxiety and attention span. Some small hypothalamic proteins have been identified tentatively in the third ventricle of the brain, which connects the hypothalamus with the thalamus, a re-gion also within the limbic system. The stunning pic-tures on page 65, taken with an electron microscope, show two close-ups of action in the third ventricle. The diagram on page 73 may help clarify some of the brain anatomy just described.

There are reasons to think that the beginnings of altruistic behavior are in the limbic system. Indeed, with rare exceptions (chiefly the social insects), mammals and birds are the only organisms to devote substantial attention to the care of their young—an evolutionary development that, through the long period of plasticity which it permits, takes advantage of the large information-processing capability of the mammalian and primate brains. Love seems to be an invention of the mammals.*

'' This rule on the relative parental concern of mammals and reptiles is, however, by no means without exceptions. Nile crocodile mothers carefully put their fresh hatchlings in their mouths and carry them to the comparative safety of the river waters; while Serengeti male lions will, upon newly dominating a pride, destroy all the resident cubs. But on the whole, mammals show a strikingly greater degree of parental care than do reptiles. The distinction may have been even more striking one hundred million years ago.

traces. The largest adults weigh about 135 kilograms (300 pounds), are three meters (about 10 feet) long and live perhaps to be centenarians. To protect its eggs, the dragon digs trenches from two to as much as nine meters (almost 30 feet) deep—probably a de-fense against egg-eating mammals (and themselves: Adults are known occasionally to stalk a nest-hole, waiting for the newly hatched young to emerge and provide a little delicacy for lunch). As another clear adaptation to predators, the dragon hatchlings live in trees.

The remarkable elaboration of these adaptations shows clearly that dragons are in trouble on the planet

Varanus komodoensis, the Komodo dragon, Komodo Island, Indonesia. Courtesy of The American Museum of Natural History

St. George slaying the Dragon, by Donatello from the Chiesa di Or San Michele, Florence.PHOTO ALINARI

Earth. The Komodo dragon lives in the wild only in the Lesser Sunda Islands.* There are only about 2,000 of them left. The obscurity of their locale immediately suggests that dragons are near extinction because of mammalian, chiefly human, predation, a conclusion borne out by their history over the last two centuries. All dragons with less extreme adaptations or less remote habitats are dead. I even wonder whether the system-atic separation of brain mass for a given body mass between mammals and reptiles (see chart on page 39) might not be the result of a systematic extinction of bright dragons by mammalian predators. In any case, it is very likely that the population of large reptiles has been declining steadily since the end of the Mesozoic Age, and that there were many more of them even one or two thousand years ago than there are today.

The pervasiveness of dragon myths in the folk legends of many cultures is probably no accident. t

* It is in the Greater Sunda Islands—more specifically Java— that the first specimen of Homo erectus, with an endocranial volume of almost 1,000 cc, was found by E. Dubois in 1891.

t Curiously, the first representative skull of Peking man— the Homo erectus whose remains are clearly associated with the use of fire—was discovered by Weng Chung Pei late in 1929

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The Temptation by a man-serpent and the expulsion from Eden. Michelangelo, from the ceiling of the Sistine Chapel.

SCALA/EP A

The implacable mutual hostility between man and dragon, as exemplified in the myth of St. George, is strongest in the West. (In chapter 3 of the Book of Genesis, God ordains an eternal enmity between rep-tiles and humans.) But it is not a Western anomaly. It is a worldwide phenomenon. Is it only an accident that the common human sounds commanding silence or attracting attention seem strangely imitative of the hissing of reptiles? Is it possible that dragons posed a problem for our protohuman ancestors of a few mil-lion years ago, and that the terror they evoked and the deaths they caused helped bring about the evolution of human intelligence? Or does the metaphor of the serpent refer to the use of the aggressive and ritualistic reptilian component of our brain in the further evolu-tion of the neocortex? With one exception, the Genesis account of the temptation by a reptile in Eden is the only instance in the Bible of humans understanding the language of animals. When we feared the dragons, were we fearing a part of ourselves? One way or an-other, there were dragons in Eden.

in Sinkiang Province, China, in a place called the Mountain of Dragons.

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The most recent dinosaur fossil is dated at about sixty million years ago. The family of man (but not the genus Homo) is some tens of millions of years old. Could there have been manlike creatures who actually encountered Tyrannosaurus rex? Could there have been dinosaurs that escaped the extinctions in the late Cretaceous Period? Could the pervasive dreams and common fears of "monsters," which children de-velop shortly after they are able to talk, be evolutionary vestiges of quite adaptive—baboonlike—responses to dragons and owls?

What functions do dreams serve today? One view, published in a reputable scientific paper, holds that the function of dreams is to wake us up a little, every now and then, to see if anyone is about to eat us. But dreams occupy such a relatively small part of normal sleep that this explanation does not seem very com-pelling. Moreover, as we have seen, the evidence points just the other way: today it is the mammalian preda-tors, not the mammalian prey, who characteristically have dream-filled sleep. Much more plausible is the computer-based explanation that dreams are a spill-over from the unconscious processing of the day's ex-perience, from the brain's decision on how much of the daily events temporarily stored in a kind of buffer to emplace in long-term memory. The events of yester-day frequently run through my dreams; the events of

* Since writing this passage I have discovered that Darwin expressed a similar thought: "May we not suspect that the vague but very real fears of children, which are quite independent of experience, are inherited effects of real dangers and abject super-stitions during ancient savage times? It is quite conformable with what we know of the transmission of formerly well-developed characters, that they should appear at an early period of life, and afterwards disappear"—like gill slits in human embryology.

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two days ago, much more rarely. However, the buffer- dumping model seems unlikely to be the whole story, because it does not explain the disguises that are so characteristic of the symbolic language of dreams, a point first stressed by Freud. It also does not explain the powerful affect or emotions of dreams; I believe there are many people who have been far more thor-oughly frightened by their dreams than by anything they have ever experienced while awake.

The buffer-dumping and memory-storage functions of dreams have some interesting social implications. The American psychiatrist Ernest Hartmann of Tufts University has provided anecdotal but reasonably per-suasive evidence that people who are engaged in in-tellectual activities during the day, especially unfamiliar intellectual activities, require more sleep at night, while, by and large, those engaged in mainly repetitive and intellectually unchallenging tasks are able to do with much less sleep. However, in part for reasons of organizational convenience, modern societies are struc-tured as if all humans had the same sleep require-ments; and in many parts of the world there is a satisfying sense of moral rectitude in rising early. The amount of sleep required for buffer dumping would then depend on how much we have both thought and experienced since the last sleep period. (There is no evidence that the causality runs backwards: people drugged with phenobarbital are not reported, during interstitial waking periods, to perform unusual intel-lectual accomplishments.) In this respect it would be interesting to examine individuals with very low sleep needs to determine whether the fraction of sleep time they spend dreaming is larger than it is for those with normal sleep requirements, and to determine whether their amount of sleep and dream time increases with the quality and quantity of their learning experiences while awake.

Michel Jouvet, a French neurologist at the University of Lyons, has found that dream sleep is triggered in

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the pons, which, while it resides in the hindbrain, is a late and essentially mammalian evolutionary develop-ment. On the other hand, Penfield has found that' electrical stimulation deep into and below the temporal lobe in the neocortex and limbic complex can produce a waking state in epileptics very similar to that of dreams denuded of their symbolic and fantastic aspects. It can also induce the deja vu experience. Much of dream affect, including fear, can also be induced by such electrical stimulation.

I once had a dream that will tantalize me forever. I dreamt I was idly thumbing through a thick history text. I could tell from the illustrations that the work was moving slowly, in the usual manner of such text-books, through the centuries: classical times, Middle Ages, Renaissance and so on, gradually approaching the modern era. But then there was World War II with about two hundred pages left. With mounting excitement I worked my way more deeply into the work until I was sure that I had passed my own time. It was a history book that included the future—like turning the December 31 page of the Cosmic Calendar and finding a fully detailed January 1. Breathlessly I attempted literally to read the future. But it was im-possible. I could make out individual words. I could even discern the serifs on the individual characters. But I could not put the letters together into words or wordi together into sentences. I was alexic.

Perhaps this is simply a metaphor of the unpredicta-bility of the future. But my invariable dream experience is that I am unable to read. I can recognize, for ex-ample, a stop sign by its color and its octagonal shape, but I cannot read the word STOP, although I know it is there. I have the impression of understanding the meaning of a page of type, but not by reading it word by word or sentence by sentence. I cannot reliably perform even simple arithmetic operations in the dream state. I make a variety of verbal confusions of no apparent symbolic significance, like mixing up

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Schumann and Schubert. I am a little aphasic and entirely alexic. Not everyone I know has the same cognitive impairment in the dream state, but people often have some impairment. (Incidentally, individu-als who are blind from birth have auditory, not visual dreams.) The neocortex is by no means altogether turned off in the dream state, but it certainly seems to suffer important malfunctions.

The seeming fact that mammals and birds both dream while their common ancestor, the reptiles, do not is surely noteworthy. Major evolution beyond the reptiles has been accompanied by and perhaps re-quires dreams. The electrically distinctive sleep of birds is episodic and brief. If they dream, they dream for only about a second at a time. But birds are, in an evolutionary sense, much closer to reptiles than mam-mals are. If we knew only about mammals, the argu-ment would be more shaky; but when both major taxonomic groups that have evolved from the reptiles find themselves compelled to dream, we must take the coincidence seriously. Why should an animal that has evolved from a reptile have to dream while other ani-mals do not? Could it be because the reptilian brain is still present and functioning?

It is extremely rare in the dream state that we bring ourselves up short and say, "This is only a dream." By and large we invest the dream content with reality. There are no rules of internal consistency that dreams are required to follow. The dream is a world of magic and ritual, passion and anger, but very rarely of skepti-cism and reason. In the metaphor of the triune brain, dreams are partially a function of the R-complex and the limbic cortex, but not of the rational part of the neocortex.

Experiments suggest that as the night wears on our dreams engage increasingly earlier material from our past, reaching back to childhood and infancy. At the same time the primary process and emotional content of the dream also increase. We are much more likely

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to dream of the passions of the cradle just before awakening than just after falling asleep. This looks very much as if the integration of the day's experience into our memory, the fOrging of new neural links, is either an easier or a more urgent task. As the night wears on and this function is completed, the more affecting dreams, the more bizarre material, the fears and lusts and other powerful emotions of the dream material emerge. Late at night, when it is very still and the obligatory daily dreams have been dreamt, the gazelles and the dragons begin to stir.

One of the most significant tools in studying the dream state was developed by William Dement, a Stanford University psychiatrist, who is as sane as it is possible for a human being to be, but who bears an exceedingly interesting name for a man of his pro-fession. The dream state is accompanied by rapid eye movements (REM), which can be detected by elec-trodes taped lightly over the eyelids in sleep, and by a particular brain wave pattern on the EEG. Dement has found that everyone dreams many times each night. On awakening, an individual in the midst of REM sleep will usually remember his dream. EVen people who claim never to dream have been discovered by REM and EEG criteria to dream as much as any-one else; and, when awakened at appropriate times, they admit with some surprise to having dreamt. The human brain is in a distinct physiological state while dreaming, and we dream rather often. While perhaps 20 percent of the subjects awakened during REM sleep do not recall their dreams, and some perhaps 10 percent of subjects awakened during non-REM sleep report dreams, we will, for convenience, identify REM and accompanying EEG patterns with the dream state.

There is some evidence that dreaming is necessary. When people or other mammals are deprived of REM sleep (by awakening them as soon as the characteristic REM and EEG dream patterns emerge), the number of initiations of the dream state per night goes up, and,

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in severe cases, daytime hallucinations—that is, waking dreams—occur. I have mentioned that the REM and EEG patterns of dreams are brief in birds and absent in reptiles. Dreams seem to be primarily a mammalian functiost. What is more, dream sleep is most vigorously engaged in by human beings in the early postnatal period. Aristotle stated quite positively that infants do not dream at all. On the contrary, we find they may be dreaming most of the time. Full-term newborn babies spend more than half their sleep time in the REM dream state. In infants born a few weeks pre-mature, the dream time is three-quarters or more of the total sleep time. Earlier in its intrauterine existence, the fetus may be dreaming all the time. (Indeed, newborn kittens are observed to spend all of their sleep time in the REM stage.) Recapitulation would then suggest that dreaming is an evolutionarily early and basic mammalian function.

There is another connection between infancy and dreams: both are followed by amnesia. When we emerge from either state, we have great difficulty re-membering what we have experienced. In both cases, I would suggest, the left hemisphere of the neocortex, which is responsible for analytic recollection, has been functioning ineffectively. An alternative explanation is that in both dreams and early childhood we experience a kind of traumatic amnesia: The experiences are too painful to remember. But many dreams we forget are very pleasant, and it is difficult to believe that infancy is that unpleasant. Also some children seem capable of remembering extremely early experiences. Memories of events late in the first year of life are not extremely rare, and there are possible examples of even earlier recollections. At age three, my son Nicholas was asked for the earliest event he could recall and replied in a hushed tone while staring into middle distance, "It was red, and I was very cold." He was born by Caesarean section. It is probably very unlikely, but I wonder whether this could just possibly be a true birth memory.

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At any rate, I think it is much more likely that child-hood and dream amnesia arise from the fact that in those states our mental lives are determined almost en-tirely by the R-complex, the limbic system and the right cerebral hemisphere. In earliest childhood, the neocortex is underdeveloped; in amnesia, it is impaired.

There is a striking correlation of penile or clitoral erection with REM sleep, even when the manifest dream content has no overt sexual aspects whatever. In primates, such erections are connected with sex (of course!), aggression and the maintenance of social hierarchies. I think that when we dream there is a part of us engaged in activities rather like those of the squirrel monkeys I saw in Paul MacLean's laboratory. The R-complex is functioning in the dreams of humans; the dragons can be heard, hissing and rasping, and the dinosaurs thunder still.

One excellent test of the merit of scientific ideas is their subsequent validation. A theory is put forward on fragmentary evidence, then an experiment is per-formed, the outcome of which the proposer of the theory could not know. If the experiment confirms the original idea, this is usually taken as strong support for the theory. Freud held that the great majority, perhaps all, of the "psychic energy" of our primary-process emotions and dream material is sexual in origin. The absolutely essential role of sexual interest in providing for the propagation of the species makes this idea neither as silly .nor as depraved as it appeared to many of Freud's Victorian contemporaries. Carl Gustav Jung, for example, held that Freud had severely over-stated the primacy of sex in the affairs of the un-conscious. But now, three-quarters of a century later, experiments in the laboratories of Dement and other psychologists appear to support Freud. It would, I think, require a very dedicated puritanism to deny some connection between penile or clitoral erection and sex. It seems to follow that sex and dreams are not casually or incidentally connected but rather have deep and

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fundamental ties—although dreams certainly partake of ritual, aggressive and hierarchical material as well. Particularly considering the state of sexual repression in late-nineteenth-century Viennese society, many of Freud's insights seem hard-won and courageous as well as valid.

Statistical studies have been made of the most com-mon categories of dreams—studies which, at least to some extent, ought to illuminate the nature of dreams. In a survey of the dreams of college students, the fol-lowing were, in order, the five most frequent types: (1) falling; (2) being pursued or attacked; (3) at-tempting repeatedly and unsuccessfully to perform a task; (4) various academic learning experiences; and (5) diverse sexual experiences. Number (4) on this list seems of special and particular concern to the group being sampled. The others, while sometimes actually encountered in the lives of undergraduates, are likely to be applicable generally, even to non-students.

The fear of falling seems clearly connected with our arboreal origins and is a fear we apparently share with other primates. If you live in a tree, the easiest way to die is simply to forget the danger of falling. The other three categories of most common dreams are particularly interesting because they correspond to aggressive, hierarchical, ritualistic and sexual functions —the realm of the R-complex. Another provocative statistic is that almost half of the people queried re-ported dreams about snakes, the only nonhuman animal rating a category all to itself in the twenty most common dreams. It is, of course, possible that many snake dreams have a straightforward Freudian interpre-tation. However, two-thirds of the respondents reported explicitly sexual dreams. Since, according to Wash-burn, young primates exhibit an untaught fear of snakes, it is easy to wonder whether the dream world does not point directly as well as indirectly to the ancient hostility between reptiles and mammals.

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There is one hypothesis that seems to me consistent with all the foregoing facts: The evolution of the limbic system involved a radically new way of viewing the world. The survival of the early mammals depended on intelligence, daytime unobtrusiveness, and devotion to the young. The world as perceived through the R-complex was quite a different world. Because of the accretionary nature of the evolution of the brain, R-complex functions could be utilized or partially bypassed but not ignored. Thus, an inhibition center developed be-low what in humans is the temporal lobe, to turn off much of the functioning of the reptilian brain; and an activation center evolved in the pons to turn on the R-complex, but harmlessly, during sleep. This view, of course, has some notable points of similarity to Freud's picture of the repression of the id by the superego (or of the unconscious by the conscious), with expressions of the id made most clearly manifest in slips of the tongue, free associations, dreams and the like—that is, during the interstices of superego repression.

With the large-scale development of the neocortex in higher mammals and primates, some neocortical in-volvement in the dream state developed—a symbolic language is, after all, still a language. (This is related to the different functions of the two hemispheres of the neocortex, described in the following chapter.) But the dream imagery contained significant sexual, ag-gressive, hierarchical and ritualistic elements. The fantastic material in the dream world may be con-nected with the near-absence of direct sensory stimu-lation during dreams. There is very little reality testing in the dream state. The prevalence of dreams in in-fants would, in this view, be because, in infancy, the

16oTHE DRAGONS OF EDEN

analytic part of the neocortex is barely working. The absence of dreams in reptiles would be because there is no repression of the dream state in reptiles; they are, as Aeschylus described our ancestors, "dreaming" in their waking state. I believe this idea can explain the strangeness—that is, the differences from our waking verbal consciousness—of the dream state; its mammalian and human neonatal localization; its physiology; and its pervasiveness in man.

Human beings exhibit enough reptilian behavior as it is. If we gave full rein to the reptilian aspects of our nature, we would clearly have a low survival potential. Because the R-complex is woven so intimately into the fabric of the brain, its functions cannot be entirely avoided for long. Perhaps the dream state permits, in our fantasy and its reality, the R-complex to function regularly, as if it were still in control.

If this is true, I wonder, after Aeschylus, if the waking state of other mammals is very much like the dream state of humans—where we can recognize signs, such as the feeling of running water and the smell of honeysuckle, but have an extremely limited repertoire of symbols such as words; where we encounter vivid sensory and emotional images and active intuitive understanding, but very little rational analysis; where we are unable to perform tasks requiring extensive concentration; where we experience short attention spans and frequent distractions and, most of all, a very feeble sense of individuality or self, which gives way to a pervading fatalism, a sense of unpredictable buffeting by uncontrollable events. If this is where we have come from, we have come very far.

By Steve Rudd: Contact the author for comments, input or corrections.

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