Brain Foundational Philosophy Psychology

Quadrune Mind and the Triune Brain in Evolution

Resources for this Post

MacLean, P. D. (1990). The triune brain in evolution: Role in paleocerebral functions. New York: Plenum Press.

The quadrune mind model of consciousness blog and Study Guide.

Purpose of this Post

My general purpose for this post is to provide the interested reader statements directly from Paul D. MacLean’s magnum opus, The triune brain in evolution: Role in paleocerebral functions. Many of the reports and judgments about MacLean’s work are made by people, including scientists and journalists, who have less understanding of his neuroscience and philosophy than they believe they do. I hope this material encourages a more informed assessment of the triune brain as perhaps one of the most useful models of consciousness ever developed for understanding human behavior.

This post may have more meaning for the reader who has at least an introductory level of familiarity with neuroscientific nomenclature and research. However, its greatest value is the deep evolutionary explanations of human behavior, individually and collectively, that MacLean provides with examples immediately recognizable by everyone.


“[I]f one takes an evolutionary approach to the study of cerebral function one finds that the brains of advanced mammals comprise an interconnected amalgamation of three main analyzers that in their structure and chemistry reflect developments identified, respectively, with reptiles, early mammals, and late mammals. This triune organization suggests approaches to neurobehavioral studies that otherwise would not be apparent” (p. vii). [Emphasis added].

1: Toward a Knowledge of the Subjective Brain (“Epistemics”)

“In the human quest for a cosmic view of life, it would seem to be of primary importance to obtain a better understanding of the brain” (p. 3).

“[I]t is curious that those who most loudly warn against the possibility of nuclear war and the extinction of life, fail at the same time to articulate reasons for justifying the perpetuation of life either here or elsewhere in the universe” (p. 4). [Survival for its own sake is characteristic of a pre-Human mentality. The Human mind has a consciousness for service as a sufficient and necessary reason to be alive].

2: Specific Indications for Brain Research

“Quite a different view of the brain and its functions derives from a comparative evolutionary approach. A comparison of the brains of existing vertebrates, together with an examination of the fossil record, indicates that the human forebrain has evolved and expanded to its great size while retaining the features of three basic evolutionary formations that reflect an ancestral relationship to reptiles, early mammals, and recent mammals…. Radically different in chemistry and structure and in an evolutionary sense countless generations apart, the three neural assemblies constitute a hierarchy of three-brains-in-one, a triune brain. Based on these features alone, it might be surmised that psychological and behavioral functions depend on the interplay of three quite different mentalities….

“[T]he three formations are capable of operating somewhat independently…. If the three formations ‘are pictured as intermeshing and functioning together as a triune brain, it makes it evident that they cannot be completely autonomous, but does not deny their capacity for operating somewhat independently….’ [T]he triune relationship implies that the ‘whole’ is greater than the sums of its parts, because the exchange of information among the three brain types means that each derives a greater amount of information than if it were operating alone” (pps. 8-9). [Emphasis in the original].

“For each one of us as individuals, there is nothing so vital as subjective experience. Without the essence of subjectivity, there would be no means of realizing our existence. Since subjectivity and its associated emanations of the mind represent forms of information, they have no material substance…. If psychological information is without substance, how do we put a handle on it for scientific purposes? Here, we are saved only by the empirical evidence that there can be no communication of information without the agency of what we recognize as physical behaving entities, no matter how large or small…. Metaphorically, behaving entities and information would compare to particles and waves of quantum mechanics” (p. 10).

4: The Striatal Complex (R-complex) Origin, Anatomy, and Question of Function

“In addressing the question as to what are similar parts of the striatal complex in reptiles, birds, and mammals, I will use the word corresponding rather than the conventional expression homologous…. Through long and various usage, the meaning of homologous has become unclear, being interpreted by some authors to signify ‘the same’ or ‘identical.’ In dealing with different taxa of animals one can say ‘corresponding’ with respect to structures identified by a particular set of attributes, without implying that they are developed to the same extent or have the same degree of complexity in their organization” (p. 37). [Emphases in the original].

5: The Mammal-like Reptiles (Therapsids)

“The mammal-like reptiles (Synapsida) are of great human interest because they are so close to the roots of our family tree. Despite their genealogical significance, these long-extinct animals, particularly the forms known as the therapsids, have received little attention in books on evolution, and compared with dinosaurs and some other reptilian species, are relatively unknown” (p. 80).

“[I]t is to be recalled that the Greek word phylon is the name for a tribe or race, and that phylogeny refers to the evolutionary history of an organism or group of organisms…. [O]ne of the most advanced therapsids, cynodont [is] regarded to be close to the phylogenetic boundary between reptiles and mammals” (pps. 81-82). [phylum New Latin, from Greek phylon tribe, race. 1a: a direct line of descent within a group b: a group that constitutes or has the unity of a phylum specificallya primary category in biological taxonomy especially of animals that ranks above the class and below the kingdom].

6: Reptilian Behavior as Typified by Lizards

“Because of their protective and survival value, submissive displays are recognized as an indispensable part of an animal’s behavioral repertoire. Their value is that in signaling compliance, they serve to forestall, reduce, or terminate the punishing, and potentially deadly, actions of a dominating animal” (p. 112).

8: A Week in the Life of a Giant Komodo Dragon

“In view of the reciprocal innervation of structures involved in oral and sexual functions… it is not surprising that the increased level of excitement among a group of monitors around carrion seems to result in a mixture of feeding and sexual activity” (p. 133). [Emphasis added].

9: Other Special Forms of Basic Behavior

“Among birds and mammals, immature animals with various kinds of blemishes (strangeness) may be killed or driven off from the home territory by continual harassment….” (p. 141). [Compare Chicago’s “ugly laws” and human infants’ “stranger anxiety”].

10: Six General Forms of Basic Behavior

“The word isopraxic may seem a little forbidding the first time that it is encountered. It means simply ‘performing or acting in a like manner,’ ‘doing something the same way,’ ‘behaving in the same way.’ I found myself resorting to the use of the term when I needed a word that was purely descriptive and had no causal overtones. There are no dictionary words that do the work of isopraxis. The word imitation, for example, not only fails to convey the desired meaning, but also has acquired so many ‘explanatory’ connotations that it is of limited usefulness. For instance, one psychological book… begins by stating, ‘All human behavior is learned.’ According to this doctrine, all human imitation would be ascribed to learning” (p. 143). 

“Group isopraxis among lizards is illustrated by the simultaneous head nodding response of several juvenile and females to the display of a territorial male lizard. It occurs with as much unison as the group gobbling response of tom turkeys or the hand clapping response of human beings” (p. 144). [See ISOPRAXISM by the Center for Nonverbal Studies. Also, compare “parallel play” among toddlers].

“In biology the word tropism (derived from the Greek word tropos meaning ‘a turning’) is used to refer to an unexplained positive or negative response to a stimulus. The turning of a plant toward sunlight is an example of a positive tropism. The word is also used to signify an inborn (innate) inclination” (p. 145).

16: Human-Related Questions

“When ethologists draw parallels between animal and human behavior, they may be criticized for equating animals and human beings. Comparative neurologists are subject to the same kind of criticism when they give emphasis to anatomical and biochemical similarities of different parts of the brain in animals and human beings. In neither case is it the intention to equate animals and humans. Rather it is regarded as a reasonable assumption that if particular brain tissue from a variety of species conforms generally in its constituents, construction, and connections, it may have corresponding functions. This will recall what was said in Chapter 4 when discussing the meaning of homology” (p. 228).

“If, as claimed, all human behavior is learned, then it must be explained why human beings with all their intelligence and culturally determined behavior, continue to do all of the ordinary things that animals do and show the same kinds of proclivities” (p. 229).

“[In reviewing] [t]he special and general forms of basic behavior…. one is quickly reminded of the dearth of systematic observations for a number of items. Take, for example, ‘place-preference’ behavior [in lizards]. Exclusive of ‘father’s chair’ and like examples from the popular media, one would in most instances have to resort to biographical material for illustrations” (p. 229).

“To judge by some writings, there continues to be heated debate as to whether or not human beings are naturally territorial….

“The human use of symbols affords unlimited boundaries to protected ‘conceptual space.’ Even the symbols themselves may reach large proportions, as, for example, the mile-long numeral ‘1’ that an American division carved in a Vietnam forest. In addition to our personal space and domestic space about which we feel possessive and protective, we incorporate into the scheme of belongingness the boundaries of a town, city, county, state, country, offshore areas, and now in modern times the territory of outer space. To this list may be added the space that we assign to schools, churches, clubs, and the like…. Many teachers and scientists have the reputation of establishing intellectual and research territories and protecting them with all their might. If human beings are not born with some degree of territorial proclivity, it is remarkable that there is so much preoccupation with trespass and no-trespass and that in every advanced culture complex legal systems and a whole body of law have evolved for settling disputes regarding ownership of lands and possessions” (p. 231). [Compare the archetypal athletic locker rooms where players yell out what they will do to teams coming into “our house!”].

“A territorial animal usually has a routine for patrolling its territory…. The Komodo dragon patrols its core area…. [M]ammals may also patrol their territories or extended parts of their domains, as is well exemplified by wolves….

“Goodall and her colleagues have reported patrolling on the part of the chimpanzees living in the wild. ‘Perhaps,’ they remark, ‘the most striking characteristic of patrolling chimpanzees is the silence which they maintain for well over 3 hours.’ Even a charging display will be performed in silence. Among human beings, regular patrolling of territory is best illustrated by military groups” (pp. 231-232). [Emphasis added].

“As in the case of lizards, the stilted, staccato steps of the displays of the great apes seem to carry the message of a series of exclamation marks. The Schrägstellung gait of the Komodo dragon… calls to mind the goose step of a military parade. The question naturally arises as to whether the striking similarity between the challenge displays of animals as diverse as lizards and gorillas represent ‘convergent’ or ‘parallel’ evolution. Among different species the sideways presentation and the stilted, staccato steps have such an uncanny resemblance that it would almost seem that the challenge display had been genetically packaged and handed up the phylogenetic tree of mammals” (pp. 232-233).

“As ethologists repeatedly emphasize, the struggle for territory is, in the lives of numerous species, a necessary first step for courtship, mating, and breeding…. Musical comedy provides exaggerated examples of different aspects of human courtship—the swagger and puffed-out chest of the male, the hip-swinging walk of the female….

“It is of comparative interest that one can trace back to reptiles a rear-end display of the female… that suggests a similar presentation seen in the pygmy marmoset, Old World monkeys, and the great apes. The posterior display may be used by female primates as a defiant or ‘put-down’ gesture. Chaucer provides a human example in his Miller’s Tale” (p. 235). [Compare the posterior display as a “put-down” by the act of “mooning,” which may be more preferred by males].

“[R]eptiles are slaves to routine, precedent, and ritual. Obeisance to precedent often has survival value…. If, for example, a particular crevice served as an escape from a predator on one occasion, it may do so again….

“Many people recognize that they have a tendency to engage in particular acts that were successful in getting them out of bad situations. In the course of time, many of these acts become established as rituals and are incorporated into the daily routine. An outside observer might regard such rituals as superstitious acts….

“For someone not in the legal profession it may not seem clear why a particular case cannot be decided on its own merits. Instead, much time and money are spent in searching for precedents. Why must it be that one must uncover the case of some obscure individual living years ago and in some remote place to prove that one’s own case has some merit? Lawyers will explain that ‘the law’ likes to be evenhanded, to be as fair as possible to all parties. This, they claim, is best assured by trying to find a similar case that might have been decided by a particularly renowned judge or by one of the highest courts. The greater the authority, the greater the weight of the judgement. What they fail to emphasize is that whoever sits in judgment derives great reassurance if it can be shown that the ruling on a similar case survived an appeal” (p. 237). [Emphasis in the original].

“Tropistic behavior is characterized by positive or negative responses to partial or complete representations, whether alive or inanimate…. [H]ow a cock rainbow lizard responds to a colored, bobbing dummy as though it were another territorial male…. Such responses need not depend on visual representations. I have seen tom turkeys perform the entire copulatory act in vacuo [away from or without the normal context or environment—Oxford Languages] upon walking onto an area of crushed stone or coarse, dry straw. Presumably, the material under foot that triggered the response gave the impression of the sharp pinfeathers on the back of a hen turkey…. For human beings a fetish may induce sexual activity.

“In Chapter 10 ‘fixed action patterns’ and ‘imprinting’ were cited as examples of tropistic behavior. Sensitive to the criticism of traditional psychologists, ethologists have tended to sidestep the question of ‘instinctive’ responses in human beings. When pressed to give examples of innate human responses, they commonly recite a list of behavioral developments in infants, including references to critical times in the life of the child when it begins to smile, sit up, walk, speak, and so forth. Much has been made of the infant’s tropistic responses to the features of the face, with the infant at first smiling in response to two (or even three) round circles representing the human eyes, and later requiring more and more detail of the human face for elicitation of the smiling response. 

“Since there is no opportunity to observe human beings growing up in isolation it is not evident how it can ever be established that beyond the age of infancy there exist naturally occurring tropistic responses and other kinds of propensities. Consequently, when making a case for human tropistic propensities, students of human ethology may draw upon illustrations from the visual and performing arts, commercial advertising, and various other sources…. cubist painting…. inkblots of a Rorschach test” (pp. 239-240). [See our discussion proposing the presence of tropistic behavior in humans in footnote #2 of our QM and the Four Steps—and Missteps—to New Behavior post].

“[D]isplacement behavior (alias adjunctive behavior) applies to repetitious acts that seem inappropriate for a particular occasion, as exemplified by a bird’s preening in a threatening situation. Since there are indications that displacement reactions are strongly conditioned by emotional factors, the present comment upon the possible underlying mechanisms would also be appropriate for the discussion of limbic functions…. 

“Human ‘displacement’ reactions during uneasy moments may become more manageable when they are recognized for what they are—e.g., grooming and cleaning reactions such as scratching the head, rubbing the face or hands, clearing the throat, picking the nose, biting nails, spitting, and so forth…. At the institutional level displacement propensities may take the form of such time-honored procedures as appointing an ad hoc committee. It seems to be understood in universities, as well as in government, that at any one time the number of existing committees is a measure of existing tension” (p. 241).

“Ever since predation became a way of life, deceptive tactics have been indispensable to both hunter and hunted. Almost nothing is known about brain mechanisms underlying deceptive behavior, but it is quite probable that very basic circuitry will be found in the R-complex [“The protoreptilian formation is represented by a particular group of ganglionic structures located at the base of the forebrain in reptiles, birds, and mammals…” (pp. 15f)]. Metaphorically, the stalking behavior of some recent presidential assassins could be compared to that of a Komodo dragon… [G]iant Komodo lizards will relentlessly stalk a deer for days at a time or wait in ambush for hours, activities that require detailed knowledge of the terrain and a good sense of time.

“Deceptive behavior is no respecter of animals or persons…. Twice in a generation an extensive web of deceit has been exposed at the highest level of government….

“If people have learned through culture that ‘honesty is the best policy,’ why is it that they are willing to take enormous risks to practice deception? Why do the games that we teach our young place such a premium on deceptive tactics and terminology of deception? How can pupils be expected to come off the playing fields and not use the same principles in competition and struggle for survival in the classroom” (p. 242)?

17: The Limbic System in Historical Perspective

“It is popularly taught that the cerebral cortex accounts for learning and memory. At best this must be a partial truth, undoubtedly reinforced by illustrations of the ‘stupidity’ of animals such as lizards and turkeys having only a rudimentary cortex…. But dependent as they are on ‘ancestral learning’ and ‘ancestral memories,’ lizards with their R-complex and only a rudimentary cortex have a great capacity for learning…. [T]hey are able to learn the features of their territory inside and out, to recognize strangers at first sight, and so on…. It would seem, therefore, that in addition to memory and learning identified with cortical function, emphasis should be given to the ‘unlearning’ of what the species have learned to do ‘naturally’” (pp. 252-253). [Compare “socialization” and the ability to inhibit “acting out” by “civilized” humans. Also, the quadrune mind model makes an innovative distinction between intelligence and consciousness. QM states that the human brain can support four levels of consciousness: reptilian-like, old mammalian-like, new mammalian-like, and Human. Each of the pre-Human levels of consciousness can be expressed with greater or lesser intelligence. Great intelligence at a lower level of consciousness does not entail great intelligence at a higher level of consciousness. See pages 5-10 of the Study Guide and the QM and the Vital Difference between Consciousness and Intelligence post for more information].

21: Participation of Thalamocingulate Division in Family-Related Behavior

“[Recent findings indicate] that the thalamocingulate division is concerned with three forms of behavior that distinguish the evolutionary transition from reptiles to mammals—namely, (1) nursing, conjoined with maternal care, (2) audiovocal communication for maintaining maternal-offspring contact, and (3) play…. From the standpoint of human evolution, no behavioral developments could have been more fundamental because they set the stage for a family way of life with its evolving responsibilities and affiliations that has led to worldwide acculturation” (p. 380). 

28: Neocortex, with Special Reference to the Frontal Granular Cortex

“With the soaring of the world’s population, it is of interest to consider the role of play in coping with crowding. Apart from the limits of the mother in giving birth to viviparous young, the number of offspring in a mammalian family is limited by the number of nipples. It may be partially for this reason that the optimum number in mammalian social groups tends not to exceed 12…. In other words, it would appear that the adoption of a family way of life has made it awkward for most mammals to adapt to crowds. Even herd animals tend to group as families. When human beings meet in large numbers, they seem to do best in situations in which they are feeding together, as at feasts and music festivals; or, taking advantage of the mammalian trait of play, are engaged in local, national, or international games, including the Olympic Games. But even in the case of international games, there appears to be a primitive, childlike, fine line between enjoying fun at play and getting mad and fighting. Hence, we have seen international games become a political means of displaying national will in showdown situations” (p. 560). [Emphasis added].

“In regard to the motivational and affective aspects of planning, it is to be emphasized that because of its respective linkage to the amygdalar and thalamocingulate divisions of the limbic system, the frontal association cortex might be expected, in the former case, to function ‘selfishly’ in terms of self-survival or, in the latter case, altruistically on behalf of others. Planning and saving for the day when one would no longer be earning a living would serve as an example of a concern for self-survival…. Performing a like exercise on behalf on one’s family would exemplify an altruistic (affective) concern in long-range planning…” (pp. 560-561).

Altruism… empathy… : these are almost new words, reflecting the acceleration of the humanitarian movement…. [It] is suggested that through the neofrontal connections with the thalamocingulate division, a parental concern for the young generalizes to other members of the species, a psychological development that amounts to an evolution from a sense of responsibility to what we call conscience. What is substantially new in the known history of biology is that this concern extends not only to the human family, but to all living things—an evolutionary turnabout that could affect a turnabout in what has heretofore seemed a vicious life-death struggle recognized as the struggle between good and evil” (pp. 561-562). 

29: Implications for Future Thinking in Regard to Epistemics and Epistemology

“A person working in the brain-related sciences… cannot avoid the realization that in the final analysis, everything reduces to subjectivity and that there is no rigorous way of defining a boundary between the subjective and what is regarded as objective.

“This same statement must be cast in the light of how we regard the substance of the brain itself….

“because there is no known means of circumventing the problem of self-reference” (pp. 570-571).

“Time and space, for example, do not exist in the immediately perceived behaving entities, but rather represent information derived from the behaving entities of the brain. When so understood, there is no resulting contradiction with respect to the possibility of immaterial information having the capacity to generate immaterial information without the intermediary of ‘behaving entities’” (p. 576). [Emphases in the original. See Chapter 2, page 10 excerpt above. This statement by MacLean seems to support the panpsychistic philosophy of consciousness as used by the quadrune mind model].

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