© 1975-1979, 2008 Robert A. Freitas Jr. All Rights Reserved.

Robert A. Freitas Jr., Xenology: An Introduction to the Scientific Study of Extraterrestrial Life, Intelligence, and Civilization, First Edition, Xenology Research Institute, Sacramento, CA, 1979; http://www.xenology.info/Xeno.htm

14.1.2  The Triune Brain

Even assuming that evolution on this world has selected the optimum basic configuration for neural components in the development of intelligence, we cannot expect the specifics of brain development elsewhere to exactly parallel our own. Yet it is fascinating to consider how much of what we are today has been dictated by our neuroevolutionary past.

Among chordates, the most ancient component of the central nervous system is the plug-in spinal cord. As noted above, all sorts of interesting subsystems and advanced modifications could be hooked on as the organism grew in size and complexity. But it must be borne in mind that evolution is a tendentious, almost bureaucratic, process. Once something novel has been invented, it's generally retained and not thrown away. The new is built upon the old, but does not replace it.

Dr. Paul MacLean, chief of the Laboratory of Brain Evolution and Behavior at the National Institute of Mental Health, believes that this is exactly how the human brain evolved over the years.²⁵⁵⁹ His theory of the "triune brain" is one of the most xenologically important developments in our understanding of the emergence of human intelligence. This theory, which neuroanatomists agree is a gross oversimplification of reality, nevertheless provides real in sight into the nature and potential diversity of alien minds.

MacLean begins by pointing out that the simplest fishes have small add-on lumps of neural cells which comprise its limited brain. These lumps are in two sections which biologists call the brain stem and the midbrain. The brain stem and midbrain, together with the spinal notochord common to all chordates, are probably the minimum amount of equipment necessary to operate any vertebrate larger than a small fish. MacLean groups together these three components and calls them the "neural chassis."

The scientist believes that the story of man’s brain involves the slow accretion, over evolutionary timescales, of three successive and overlapping brain structures that were plugged in to the neural chassis, modular-style -- but which were never removed once nature was through with them. Following each evolutionary step, the older more primitive modules were left in place and new ones plugged in on top of them (Figure 14.2).

The human triune brain, explains MacLean, "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."²⁵⁵⁹ Each represents a major new evolutionary step. Because the present human brain has this peculiar tripartite structure, and since each of the primitive components is still present and operational, "we are obligated to look at ourselves and the world through the eyes of three quite different mentalities."

The earliest of the three human plug-in brain systems has been called the "reptilian brain." This structure surrounds the midbrain in the neural chassis and probably arose 300 million years ago with the rise of the first reptiles.

The second unit was laid over the first, eventually taking over the higher organismic functions. This unit is called the "limbic brain," and probably arose about 150-200 million years ago with the emergence of the first mammals on Earth.

The third and final unit, which appears in most of the higher mammals, is the neocortex. This structure began to develop about 30 million years ago as a small growth on top of the limbic system, slowly spreading, enlarging, becoming more massive over time, finally reaching the peak of accelerated development a few million years ago with the rise of man. The neocortex now completely encases the underlying layers of reptilian and limbic brain. It is more central to neurological control functions in humans than the other two systems.

Each of these brains has a different way of looking at the world. Each has a different mode of operation. And yet each is functioning still within our heads, causing untoward psychological conflict and, as we shall see, much of what is interesting about human behavior.

The reptilian brain, for example, is now known to play a major role in determining aggressive behavior, territoriality, ritualism, and the establishment of social hierarchies.²⁵⁵² This dull, plodding neurosystem, with its slavish dependence on programmed "hard-wired" behaviors, may be responsible for a great deal of human ritualistic and hierarchical behavioral patterns -- our political institutions and bureaucracies, our fertility dances, and our unparalleled aggressiveness and competitiveness. The reptilian mind is not characterized by "powerful passions and wrenching contradictions, but rather by a dutiful and stolid acquiescence to whatever behavior its genes and brains dictate."²⁵⁵²

The limbic system, which overlays the reptilian brain, appears to generate strong, vivid emotions of various kinds. This is the seat of the endocrine glandular system, which is governed by the pituitary or "master gland." The amygdala, a subsidiary gland, is known to regulate aspects of fear, aggression, and attack behavior. Hormones released into the bloodstream by the hypothalamus and thalamus control such diverse functions as hunger and thirst, attention span and anxiety, and visual retention.

The oldest part of the limbic brain is the olfactory cortex, which does for smell what the higher auditory and visual centers do for sound and light. The hippocampus, another limbic structure, is believed to control a wide variety of mental functions including short-term memory, sensitivity to pain, and sexual interest. There are reasons to suspect that the beginnings of individual altruism, neonatal and parental care, even love may have followed the development of the limbic system in the evolving mammalian brain.²⁵⁵²

The neocortex, home of the higher human cognitive functions, represents perhaps 85% of the entire brain volume in man. As mammals evolved this gigantic "tumor" swelled outward like a balloon, increasing the cranial volume -- and intelligence -- markedly.

The neocortical brain carries on a wide variety of highly sophisticated data processing functions. The frontal lobes are concerned with deliberation, initiative and caution, anticipation and planning, and overall regulation of complex behaviors. The parietal lobes handle spatial perception, three-dimensional orientation, and the exchange of information between the brain and the rest of the body. They also provide the ability to manipulate symbols which is so crucial to the development and use of language. The temporal lobes contain the auditory centers were acoustical data is monitored, processed, and rerouted. The occipital lobes are charged with processing visual information coming from the eyes.

What do xenobiologists have to say about all of this? It is not unreasonable to suppose that alien evolutionary patterns may also include some form of neural chassis with plug-in components. Certainly this is an adaptive course of development that encourages survival. But it is asking too much of evolutionary convergence to expect that natural selection on other planets will produce exactly the same neural chassis structural overlays as our own. ETs might have only two higher brain systems, or four, instead of our basic three. And the distribution of behavioral functions and memory subsystems will likely be vastly different.

Nevertheless, and purely as an hypothetical exercise, let us examine the kinds of alien minds we might encounter elsewhere if the three major stages of vertebrate mental development on Earth (ritual, emotional, and reasoning) prove to be more or less universal.

It has been suggested that one prerequisite for neocortical development is a stable internal body temperature -- that is, homeothermy or warm-bloodedness.⁸⁵ This hypothesis receives at least tentative confirmation by the appearance of both limbic and neocortical systems only after the rise of the warm-blooded mammals. On a world where homeothermy was never invented, the reptilian complex might eventually come to dominate the brain of sentient extraterrestrials.

Dinosaurs, bearers of the largest of the reptilian brains, are traditionally regarded as extremely dumb animals. Typical is Diplodocus, a monstrous beast weighing twelve metric tons and guided by a tiny brain the size of a golf ball. The dinosaurs ruled the Earth for a hundred million years, yet their brains advanced little during that time.

Still, we must take care to avoid "mammal chauvinism." In point of fact, there were a few dinosaur species that were slowly evolving towards higher intelligence using the reptilian brain. One good example is the species Saurornithoides, whose members weighed in at 50 kilograms with brains of about 50 grams. These small reptiles were bipedal, with four-fingered hands and an ability to catch and eat small mammals. Their intelligence has been compared to that of the modern ostrich.

On another world, given enough time and a slower introduction of homeothermy, might high alien reptilian intellects emerge? Sentient creatures in whom the R-brain dominated the others might have learned to hunt collectively and perhaps prevent the proliferation of mammals at a later date. The psychology of such creatures would be a fascinating blend of ritual and peculiar species-specific responses, and their dogged aggressiveness and unyielding devotion to duty could make them quite fearsome warriors.

Most of the mammals on Earth did quite well with only a limbic brain perched atop the ancient reptilian complex. Perhaps the neocortex isn’t necessary for higher intellect at all. What if conditions on another world were such that the limbic brain, rather than the neocortex, came to represent the highest level of brain development? How could this state of affairs ever come about?

Xenobiologists recognize that the limbic component of the mammalian brain is very closely connected with the sense of smell. It is a fact that the olfactory cortex takes up a considerable portion of the limbic brain. It’s also known that in those animals for whom scent is the primary sensory modality, such as dogs, the olfactory cortex is far more intricate and elaborated than it is in man.

In the previous chapter we suggested various environments which may tend to favor the evolution of beings who rely more heavily on olfactory, rather than visual or auditory, stimuli. These same environments, given enough time, should also tend to favor the enlargement and articulation of the olfactory centers in the limbic system which no subsequent neocortical development could ever hope to match. In other words, osmic aliens will have brains designed to handle olfactory data, which in turn implies the evolution of high limbic intelligence.

Sentience which is predominantly limbic will be more subject to emotional distractions than other forms of intellect. These extraterrestrials may be unduly concerned with ameliorating hunger, thirst, and other "creature comforts" of life. They might also be inordinately preoccupied with sex, even by the most libidinous human standards.

We see that diverse forms of alien intelligence can be imagined, simply by allowing that extraterrestrial brains may be dominated by reptilian or limbic, rather than neocortical, components. But even if ETs are predominantly neocortical, this is no guarantee that their minds will be equivalent to ours.

Reptilian creatures first appeared during the Mesozoic era on Earth, a period in our planet’s history marked by a very mild, warm, uniform climate on a global scale. Mammals didn’t take over until, so to speak, the weather turned from fair to foul. Let us imagine a world which is perpetually inclement, varying widely from hot to cold and dry to wet without respite. On such a planet, there might be significant advantage in developing homeothermy far sooner than on Earth.

If warm-bloodedness arrived early enough, perhaps even predating the rise of cold-blooded or reptilian creatures, then the rapid unfolding of biological evolution could leave the reptilian component of the brain relatively small and insignificant. ETs might have few traces of the R-complex, a few scant shards of the limbic system, and would possess brains comprised primarily of neocortical material.

These aliens would think far differently from humans, even though they share with us a large neocortical component. The ancient drives of aggression, dominance, and impulsive hierarchical organization might be wholly foreign to them, and they could have great difficulty fathoming the significance of our many cultural rituals and our religious and political institutions. To them, our emotionality would appear primitive, even barbaric.

Along similar lines, Doris and David Jonas point out that while intelligence arises because lifeforms must adapt to their environment, it will continue to evolve only so long as the adaptation is not perfect.¹⁰⁰⁰ Higher intellect leads either to greater survivability or to superior control of the environment, either of which in turn lead to a decrease in the need to develop still greater intelligence.

In the last 30 million years of terrestrial history, the neocortex of mammals has enlarged from a mere wisp to a massive structure dominating the human cranial cavity. The Jonases hypothesize that this trend will continue, because human society is not yet perfectly adapted to the technological environment it has created. The ability to comprehend and analyze increasingly complex and abstract problems is of greater selective value than ever before. The knee-jerk emotional reactions radiated by the limbic system appear maladaptive in a society in which rationality is the hallmark of success. And the ritualistic and aggressive behaviors caused by the reptilian brain seem incompatible with a healthy, undogmatic, liberal culture on a small planet with limited resources and finite territories.

So it is not unreasonable to suppose that the neocortex may continue to enlarge with the passage of future human generations. Perhaps it will eventually grow to replace most or all of the cognitive and behavioral functions presently assumed by other brain systems. The resulting intelligence, which the Jonases feel may be in the cards for humanity, may be called Homo neocorticus.

Like the ancient alien homeotherms described above, extraterrestrials whose culture is highly technologically oriented may undergo similar evolution, slowly casting off their primitive drives one by one as they become highly rational and unflappable thinkers.

It could be that the timescales in such projections are all wrong. Millions of years were required even for the abnormally rapid expansion of the human neocortex, whereas social and technical changes require time periods on the order of tens, hundreds, or thousands of years.

However, it is unlikely that the ultimate evolution of Homo neocorticus or his extraterrestrial counterpart is impossible. The very rapidity of technological processes may permit a kind of artificial evolution to an equivalent state. Advanced genetic engineering, for example, could make possible the design and development of altered humans with reduced or restricted limbic and reptilian brain components. Artificial biological brain components or bioneered modules could be used to replace ancient brain sections with more advanced neocortex-like structures. Then there is the possibility of Homo bionicus, with his snap-on input monitors, his plug-in memory modules, and his subcutaneous microcomputer logic circuits. Each of these are reasonable models of conceivable alien intelligences with whom we may someday have to learn to deal.

Last updated on 6 December 2008