What does it tell us about the meaning of life when we can now say that for the first time in the known history of biology, we are witnessing the evolution of human beings with a concern not only for the suffering and dying of their own kind, but also for the suffering and dying of all living things? – Paul MacLean
George E. P. Box famously said, “Remember that all models are wrong; the practical question is how wrong do they have to be to not be useful.”1
In this post I will argue that criticisms of Paul MacLean’s triune brain model by some neuroscientists miss the point of its revolutionary insights and their usefulness in helping us think about consciousness. The criticisms also underappreciate the value of MacLean’s innovative neurological research. (Appropriately, “MacLean” rhymes with “brain.”)
Paul MacLean as a Neuroscientist2
Many years ago I spoke on the telephone with a colleague of MacLean’s at the National Institute of Mental Health (NIMH). I told her I was a fan of his, meaning the triune brain model. She said, yes, he was very good, especially his early work. And in fact MacLean’s early work in psychosomatic disease has received significant recognition. The American Psychosomatic Society gives out an annual award in his name for outstanding neuroscience research in psychosomatic medicine. The APS notes, “Paul MacLean was a physician whose visionary neuroscientific research career at Yale Medical School and NIMH was inspired by his recognition of the importance of emotion in clinical medicine and everyday life. In 1949 he hypothesized that psychosomatic disorders arose from impairment in communication between the limbic system and neocortex. This award is intended to honor Dr. MacLean and promote the line of research that he created on emotion, the brain and physical disease.”
We see that even from his earliest neuroscientific work, MacLean was a “visionary” whose interests led him to study the “impairment in communication” between areas of the brain. This theme would continue throughout his career.
Much criticism of MacLean’s later triune brain-related neuroscience seems to be more directed at what the press said about his work than what he himself said.3 Some accusations appear to have come from people who hadn’t carefully read his work.
For example, his use of the term “correspondence” instead of “homology” for comparisons of apparently similar brain structures among species was criticized as unprofessional. However, MacLean had explained his distinction of the terms: “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” (Maclean, 1990, page 37). MacLean seems quite judicious in his use of words regarding his line of research.
He did respect words and he loved neologisms, which may have confused some colleagues. Also, he didn’t seem to have the kind of personality that one would associate with a genius brain scientist, although he was that. In 2003 I spoke to a researcher who had worked in MacLean’s Laboratory of Brain Evolution and Behavior at NIMH. He described MacLean as “not ensnared with the egoism of many of the senior researchers of our time.” (The Selected Resources section below contains some additional information regarding MacLean’s place in neuroscience.)
Perhaps MacLean’s scientific achievements were misevaluated by his peers partially because he had the heart of a philosopher in his approach to brain research. It is as a philosophically-oriented thinker that MacLean inspired the development of our quadrune mind model of consciousness.
Paul MacLean as a Philosopher of Mind
Paul MacLean entered neuroscience with a fundamentally philosophical approach. He asked the brain to answer the question, “What is the meaning of life?” (Neuroscience, itself, has only recently adopted a philosophical mind-set asking the brain to reveal the purpose of human life. There is now a wide-ranging discipline called “neurophilosophy.”4)
In Squire (1998) MacLean reflected on childhood influences in his life: “I kept wondering to myself, ‘Why do people who know better do things that they also know may get them in trouble?’ In retrospect it would seem I was perseverating on the question raised by Spinoza’s statement to the effect that all people are driven by their emotions. The persistence of that question seems to have been instrumental in steering the direction of my interest when I engaged in brain research 30 years later at the Massachusetts General Hospital (MGH)” (page 249).
Because of MacLean’s deep philosophical bent, it’s not surprising that a philosopher might compare the triune mind model with Plato’s philosophical view of the psyche, upon which Plato built his moral theory.5 From this perspective MacLean is solidly within a long philosophy of mind tradition.
Returning to MacLean’s search for the “meaning of life” issue, he reflected, “Why, I ask, with all the suffering in this world—human suffering, animal suffering—would anyone want to create life, and perpetuate life, here or elsewhere in the Universe?
“When, as usual, there are no persuasive answers, I call attention to what has been for me a comforting observation. The development of the prefrontal cortex in human beings has been shown to be involved in anticipation and planning, as well as with empathic and altruistic feelings…. [T]he evolution of prefrontal connections with the limbic ‘parental’ cortex would make it possible for a concern for the future welfare of the immediate family to generalize to other members of the species…. What does it tell us about the meaning of life when we can now say that for the first time in the known history of biology, we are witnessing the evolution of human beings with a concern not only for the suffering and dying of their own kind, but also for the suffering and dying of all living things?” [Squire, (1998), p 273. Emphasis added].
This is a statement that represents mystics (and Human beings) throughout the world—and is the inspiration of our quadrune mind model’s conception of spiritual consciousness.
The Quadrune Mind as a Useful Model of People’s Animal-like Behaviors versus Spiritual Human Behaviors
We have posted several blogs that we believe give useful descriptive and prescriptive insights to the dramatically wide range of human behaviors we see. Other attempts to “explain” these behaviors give trivial, complexly contrived, or nonmeaningful explanations; or no attempt to explain the behaviors at all, beyond “That’s just human nature.” Below are links to some of our relevant posts.
Chalmers, D. (Ed.). (Page generated 2021, June 23). Philosophy of consciousness. The PhilPapers Foundation. [A vast bibliography of scholarly articles on philosophy of consciousness].
Chalmers, D., & Bourget, D. (Eds.). (Page generated 2021, June 23). Philosophy of mind. The PhilPapers Foundation. [A vast bibliography of scholarly articles on philosophy of mind].
Cory, G. A., Jr., & Gardner, R., Jr. (Eds.). (2002). The evolutionary neuroethology of Paul MacLean: Convergences and Frontiers. Westport, CT: Praeger. [This book is an excellent contemporaneous explication of MacLean’s matured neurological science and philosophy. The book describes possible causes of neuroscience’s marginalization of MacLean and his work. Joseph LeDoux is criticized for his representation of MacLean’s research].
Goff, P. (2019). Galileo’s error: Foundations for a new science of consciousness. New York: Pantheon Books. [An eloquent philosophical argument against materialism and dualism, and for panpsychism. Goff’s philosophy of consciousness is the closest model to the quadrune mind understanding of spirituality that I am aware of].
MacLean, P. D. (1990). The triune brain in evolution: Role in paleocerebral functions. New York: Plenum Press. [MacLean’s magnum opus].
MacLean, P. D. (1998). Paul D. MacLean. In L. R. Squire (Ed.). The history of neuroscience in autobiography: Vol. 2. Paul D. MacLean (pages 244-275). San Diego, CA: Academic Press.
Naumann, R. K., et al. (2015, April 20). The reptilian brain. Current Biology. “The diversity of reptiles and their evolutionary relationship to mammals make reptilian brains great models to explore questions related to the structural and functional evolution of vertebrate neural circuits….
“Identification of conserved brain subdivisions, established by conserved signaling centers and uniquely defined by the combinatorial expression of transcription factors during development, demonstrates that all of the general brain regions found in mammals, including the cerebral cortex, have homologies in reptiles….
“Although pallial structures exist in amphibians and fish, reptiles and mammals are the only vertebrates to have a cerebral cortex with a clear, though simple, three-layered structure, similar to that of mammalian allocortex… Some lizard species exhibit pair bonding, parental care, and form families. Others construct networks of tunnels and may live in social communities like those of naked-mole rats.
“Reptiles express a number of complex behaviors normally attributed to mammals….
“In conclusion, the observation that mammalian and reptilian brains share both ancestry and a large number of functional attributes suggests that the identification of primordial (and possibly general) algorithmic principles of brain function could be helped by comparative approaches. To this end the reptilian brain, with its simpler structure, may prove invaluable to decipher fundamental questions of modern neuroscience.”
[This article represents a current body of relevant scholarly neuroscientific research. It does not cite MacLean. However, I believe it has relevance here. As with other current neuroscience it refutes details of MacLean’s triune brain model, but it seems at the same time to generally support many of the “triune brain” conclusions. I believe it may also rebut some neuroscientists’ criticisms of the triune brain model].
Newman, J. D., & Harris, J. C. (2009, January). The scientific contributions of Paul D. MacLean (1913-2007). Journal of Nervous and Mental Disease, 197, 3-5. “MacLean helped establish an approach to neuroscience essentially unknown in the United States at the time he began his research. In Europe, the field of neuroethology had arisen with primary focus on nonmammalian models… [MacLean’s] approach was clearly ethological and he emphasized the importance of preparing an ethogram, an inventory of the behavior of a species that thoroughly describes its behaviors and organizes them into categories. He was particularly interested in identifying behavioral master routines and subroutines. Although he never used the term ‘neuroethology,’ MacLean was clearly an important early pioneer in this field” (page 3).
“Several symposia have been held to honor MacLean… [A] special satellite symposium of the International Behavioral Neuroscience Society’s annual meeting held in Capri, Italy was devoted to MacLean. This led to a special issue of Physiology and Behavior…. The preface to that issue… contained a fitting expression of appreciation to MacLean and his work: ‘A special thanks is extended to this amazing scientist for opening the door to social and evolutionary neuroscience so that today’s scientists and practitioners can embark on many paths to understand more about the brain in its natural context’” (page 5).Triune brain. (last edited 2021, May 12). Wikipedia. “The triune model of the mammalian brain is seen as an oversimplified organizing theme by some in the field of comparative neuroscience. It continues to hold public interest because of its simplicity. While inaccurate in many respects as an explanation for brain activity, structure and evolution, it remains one of very few approximations of the truth we have to work with: the ‘neocortex’ represents that cluster of brain structures involved in advanced cognition, including planning, modeling and simulation; the ‘limbic brain’ refers to those brain structures, wherever located, associated with social and nurturing behaviors, mutual reciprocity, and other behaviors and affects that arose during the age of the mammals; and the ‘reptilian brain’ refers to those brain structures related to territoriality, ritual behavior and other ‘reptile’ behaviors.” [Emphases added].
- Georgiev, G. (2019, November 5). “All Models Are Wrong” Does Not Mean What You Think It Means. Start it up. “Prominent 20th century statistician George Box is often quoted as saying ‘All Models Are Wrong’ or sometimes, a bit more correctly: ‘All models are wrong, but some are useful.’… However, there is no such quote to be found in G. Box’s bibliography. The closest we get is this statement….”
- I am indebted to Paul MacLean’s son, Paul MacLean Jr., for his continued support and helpful correspondence over the years. I appreciated him and his wife meeting me and my family for a lovely lunch in the picturesque town of Niagara-on-the-Lake, Ontario, Canada. Paul provided many significant sources of commentaries on his father’s work and some of the information he shared is included in this blog. I was happy that the man Paul described was very much like the person I imagined him to be.
- Lambert, K.G. (2003). The life and career of Paul MacLean: A journey toward neurobiological and social harmony. Physiology & Behavior, 79, 343-349. “MacLean first publicly discussed his idea of the triune brain in 1969 when he delivered a series of lectures at Queens University in Kingston, Ontario (Ref.  reviewed in Ref. ).“Much to MacLean’s surprise, the notion of this multifaceted brain became wildly popular in the press. The media, however, overemphasized MacLean’s suggestion that we are under the control of three very different brains, failing to convey his ideas that these components contribute to a single, functioning brain. This confusion led him to search once again for a more defining term to use. Because triune literally means three-in-one, he chose that term for his new evolutionary brain theory . Considering that MacLean’s father was a Presbyterian minister, this term seemed perfect for his theory at the time, but he later regretted this choice due to its religious connotations .” [Bracketed notes are in the original].
- Churchland, P. S. (1986). Neurophilosophy: Toward a science of the mind/brain. Cambridge, MA: MIT Press. Patricia Churchland is credited with coining the term neurophilosophy. Although she unites mind/brain as the object of study, she is ardently on the side of brain science as the place to find the answers, designating a lesser place to mind philosophy.
- Laidlaw, E. (2012). Plato’s Neurobiology. Philosophy now: A magazine of ideas. “The three parts of the brain are in communication with each other – sometimes. Howard Bath says that the highway from the survival and emotional brains to the rational brain develops much earlier than the path from the rational part to the emotional and survival parts. For our first two decades of life, therefore, the survival and emotional brains are calling most of the shots, most of the time. To mature, the emotional and rational parts of the brain require development of their neural highways. This development comes from interacting with other brains – other people. So, even at this very basic level, we need each other. More specifically, the interaction is most needed when we are young, while our brains are developing. Thus Bath advises: ‘A large part of the task of parents, teachers, counselors, and mentors is to help youth finish wiring their brains. The most powerful effect on positive brain development comes from connections with positive, caring adults and peers’ (Howard Bath, ‘Our Amazing Brains’, Reclaiming Children and Youth 14.3, 2005).
“Continuous and positive interaction during the first year and a half of life is critical to moral development, since early experiences program us to react to our environment in predictable ways. If our early relationships are negative, we develop neural pathways that lead us toward unsociable, sometimes violent actions – a.k.a. ‘adaptively generated primitive actions’. If we have no early relationships, our brains literally won’t grow the neurons necessary for us to relate to the social world….
“In the Republic the psyche (mind or soul) of a person is described in terms of function. Socrates describes the psyche as having three parts: reason, spirit and appetite, for which he employs the metaphor of reason being a charioteer guiding the chariot of the psyche as it is being pulled by two horses, spirit and appetite (or will and desire). The function of the rational part is to be wise, that is to rule with insight on behalf of the entire soul. The courageous or high-spirited protective part is subject to, but an ally of, the rational part. The appetitive part is ruled over by the other two. Compare this concept with the concept of the triune brain. The ‘reason’ part of the Platonic psyche can be said to be equivalent to the rational brain, the neocortex; the ‘spirited’ part of the psyche with the emotional brain, or limbic system; and the basic, ‘appetitive’ part of the mind, with the survival or reptilian part of the brain. You might agree that the analogy makes a close fit…. [Plato’s reason, spirit, and appetite find familiar company in Freud’s ego, superego, and id. I believe even more closely related to MacLean’s triune brain model and the quadrune mind model is Antonio Damasio’s three layered theory of consciousness. Interestingly, in the Wikipedia article precursors of “Damasio’s tri-level view of the human mind” are discussed with no mention of MacLean or the triune brain, although there appears to be an oblique criticism of MacLean’s focus on the limbic system as “less sophisticated.” As far as I’m aware MacLean does not show up in contemporary neuroscientific literature on consciousness. It appears that MacLean’s contributions to philosophy of mind are ignored because of a neuroscience reductionist-based bias. I guess neuroscientists can be as “narrow-minded” as anyone else].
[Laidlaw concludes] “Perhaps the most obvious philosophical objection to these brain-based conclusions is that, in using neuroscience to guide ethics, this Neuro-Moral Theory commits the naturalistic fallacy. Can our survival instincts and our need to thrive tell us what we morally ought to do? The debate over whether or not it is a fallacy to derive conclusions about how the world ought to be solely from factual claims about how the world is began with David Hume three centuries ago. Hume warned of the logical difficulty of this move, pointing out that nothing can appear in the conclusion of an argument which does not appear in its premises. So is it logically possible to deduce how we ought to raise and judge children from the experimental results of neuroscience? Yes, it is. The Neuro-Moral Theory takes seriously the constraints of human biology and, rather than committing the fallacy of deriving what we ought to do from what is the case, is supported by the philosophical wisdom that ‘ought implies can’. That is, what we are morally obligated to do must be within our grasp. What I’m suggesting is that we use the lessons of neuroscience to guide our decisions about the education of children, and about our moral assessment of them. Like Plato I am suggesting that being moral requires good thinking, which (unlike Plato) I say requires good brain development.”[Emphases in the original. Laidlaw’s neurological representation of the brain is neurologically outdated, using a variation of MacLean’s schematic illustration of the triune brain as three nesting brains. Nevertheless, I believe that her exposition on the relationship of neural development to moral development is philosophically consistent with the spirit of the triune brain and quadrune mind models].