The Dragons of Eden

When evolutionists talk about evolution, they usually focus on the body and the DNA, but Carl Sagan in his book, The Dragons of Eden, focuses on the brain. This brain is the most important part of the human body and in terms of evolution as well. The name "The Dragons of Eden" comes from a quote in Job 30:29, "I am a brother to dragons, and a companion to owls." The brother to dragons means, to Carl Sagan, that Job is descended from reptilians. These are excerpts from this book. 


Page 37.


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 impairment, temporarily regressing the victim back several hundreds of millions of years. The ancient Greeks, whose name for the disease we still use, recognized 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 37 is made up mostly of what neuroanatomists 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 hundred and fifty million years ago. Finally, surmounting the rest of the brain, and clearly the most recent evolutionary accretion, is the neocortex. Like the higher mammals and the other primates, humans have a relatively 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 humans emerged. Aschematic 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 biain ₩o 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.


It is very difficult to evolve by altering the deep fabric of life; any change there is likely to be lethal. But fundamental change can be accomplished by the addition of new systems on top of old ones. This is reminiscent of a doctrine which was called recapitulation by Ernst Haeckel, a nineteenth-century German anatomist, and which has gone through various cycles of scholarly acceptance and rejection. Haeckel held that in its embryological development, an animal tends to repeat or recapitulate the sequence that its ancestors followed during their evolution. And indeed in human intrauterine development we run through stages very much like fish, reptiles and nonprimate mammals before we become recognizably human.


The fish stage even has gill slits, which are absolutely useless for the embryo who is nourished via the umbilical cord, but a necessity for human embryology: since gills were vital to our ancestors, we run through a gill stage in becoming human. The brain of a human fetus also develops from the inside out, and, roughly speaking, runs through the sequence: neural chassis, R-complex, limbic system and neocortex.


Page 40.  




If the preceding view is correct, we should expect the R-complex in the human brain to be in some sense 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. Despite occasional welcome exceptions, this seems to me to characterize a great deal of modern human bureaucratic 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 commonly 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 transformation 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.


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 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 hierarchical 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, 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 substantial adjustment of the relative role of each component of the triune brain is well within our powers.


Page 54.




Despite the intriguing localization of function in the triune brain model, it is, I stress again, an oversimplification to insist upon perfect separation of function. Human ritual and emotional behavior are certainly influenced strongly by neocortical abstract reasoning; analytical demonstrations of the validity of purely religious beliefs have been proffered, and there are philosophical justifications for hierarchical behavior, such as Thomas Hobbes' "demonstration" of the divine right of kings. Likewise, animals that are not human-and in fact even some animals that are not primates-seem to show glimmerings of analytical abilities. I certainly have such an impression about dolphins, as I described in my book The Cosmic Connection.


Nevertheless, while bearing these caveats in mind, it seems a useful first approximation to consider the ritualistic and hierarchical aspects of our lives to be influenced strongly by the R-complex and shared with our reptilian forebears; the altruistic, emotional and religious aspects of our lives to be localized to a significant extent in the limbic system and shared with our nonprimate mammalian forebears (and perhaps the birds); and reason to be a function of the neo-cortex, shared to some extent with the higher primates and such cetaceans as dolphins and whales. While ritual, emotion and reasoning are all significant aspects of human nature, the most nearly unique human characteristic is the ability to associate abstractly and to reason. Curiosity and the urge to solve problems are the emotional hallmarks of our species; and the most characteristically human activities are mathematics, science, technology, music and the arts-a somewhat broader range of subjects than is usually included under the "humanities." Indeed, in its common usage this very word seems to reflect a peculiar narrowness of vision about what is human. Mathematics is as much a "humanity" as poetry. Whales and elephants may be as "humane" as humans.


The triune-brain model derives from studies of comparative neuroanatomy and behavior. But honest introspection is not unknown in the human species, and if the triune-brain model is correct, we would expect some hint of it in the history of human self-knowledge. The most widely known hypothesis that is at least reminiscent of the triune brain is Sigmund Freud's division of the human psyche into id, ego and superego. The aggressive and sexual aspects of the R-complex correspond satisfyingly to the Freudian description of the id (Latin for "it"-i. e., the beast-like aspect of our natures); but, so far as I know, Freud did not in his description of the id lay great stress on the ritual or social-hierarchy aspects of the R-complex. He did describe emotions as an ego function-in particular the "oceanic experience," which is the Freudian equivalent of the religious epiphany. However, the superego is not depicted primarily as the site of abstract reasoning but rather as the internalizer of societal and parental strictures, which in the triune brain we might suspect to be more a function of the R-complex. Thus I would have to describe the psychoanalytic tripartite mind as only weakly in accord with the triune-brain model.

Perhaps a better metaphor is Freud's division of the mind into the conscious; the preconscious, which is latent but capable of being tapped; and the unconscious, which is repressed or otherwise unavailable. It was the tension that exists among the components of the psyche that Freud had in mind when he said of man that "his capacity for neurosis would merely be the obverse of his capacity for cultural development." He called the unconscious functions "primary processes."


A superior agreement is found in the metaphor for the human psyche in the Platonic dialogue Phaedrus. Socrates likens the human soul to a chariot drawn by two horses-one black, one white-pulling in different directions and weakly controlled by a charioteer. The metaphor of the chariot itself is remarkably similar to MacLean's neural chassis; the two horses, to the R-complex and the limbic cortex; and the charioteer barely in control of the careening chariot and horses, to the neocortex. In yet another metaphor, Freud described the ego as the rider of an unruly horse. Both the Freudian and the Platonic metaphors emphasize the considerable independence of and tension among the constituent parts of the psyche, a point that characterizes the human condition and to which we will return. Because of the neuroanatomical connections between the three components, the triune brain must itself, like the Phaedrus chariot, be a metaphor; but it may prove to be a metaphor of great utility and depth.

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