Triune Brain: Myth or Fact

The Triune Brain Backstory: Meet Dr MacLean…

Back in the 1960s, American physician and neuroscientist Paul D. MacLean proposed the triune brain as a model of the evolution of the vertebrate forebrain and behavior.¹

MacLean claimed our brains consist of three significant structures. (Let’s do the coaches’ hand signals 🙂 Image of human brain with three parts color coded

The reptilian complex (aka brain stem)
The paleomammalian complex (aka limbic system)
And the neomammalian complex (aka the prefrontal lobes)

MacLean’s theory stated:

The structures were sequentially added along the course of the evolution of our species (along w other mammals)
With the older parts being the brain stem, followed by the limbic system, and the newest being the prefrontal lobes
All three parts were independently conscious, and with their own specific functions:
- The reptilian part is in charge of our primal instincts
- The limbic system is in charge of our emotions
- And the neocortex: responsible for objective or rational thoughts and executive functions

All Models Are Wrong, Some Are Useful

The useful part:

The theory has been embraced by some psychiatrists and at least one leading affective neuroscience researcher. ²
The model especially appeals to psychotherapists because it seemed to give biological credence to Freud’s theory of personality with the id, ego, and superego mapping neatly onto the reptilian, limbic, and cortical brains.³
Model is used in a large % of college-level textbooks
Agile coaches love hand gestures….

Non-Academic Stuff

Many authors drew heavily on the triune brain concept in their books bringing these ideas to wider, nonacademic audiences:

Arthur Koestler made it the centerpiece of much of his work, notably The Ghost in the Machine. (1967)
Carl Sagan’s (1978) Pulitzer Prize-winning book, The Dragons of Eden,
English novelist Julian Barnes quotes MacLean in his 1982 novel Before She Met Me.
Howard Bloom, in his book The Lucifer Principle, (1995) references the concept (of the triune brain) in his explanations of certain aspects of human behavior.
Peter A. Levine uses the triune brain concept in his 1997 book Waking the Tiger to explain his somatic experiencing approach to healing trauma
Steven Johnson’s (2005) Mind Wide Open
2020 The Advice Trap By Michael Bungay Stanier – Lizard brain makes an appearance. Referencing his 2016 book The Coaching Habit Michael Bungay Stanier asks about four drivers that humans weigh to determine if a situation is safe or not:
- Tribe: “Are you with me, or against me?”
- Expectation: “Do I know what’s about to happen, or not?”
- Rank: “Are you more or less important than me?”
- Autonomy: “Do I have any say in this, or not?”
- All wrapped in references to reptile brain and higher brain functions

Additional Connections

SCARF
- David Rock, the author of Your Brain at Work, classified five areas of social experience as it applies to collaborative groups via his SCARF model along with a range of possible valences (+/-) and pre-frontal cortex responses
- Honestly, I’m a bit fuzzy if Rock is connected to MacClean’s work. If you know, ping me. I’d love to learn more…

All Models Are Wrong.

Debunking MacLean’s Triune Brain

In researching the topic, found out that since the 1970s in many circles of evolutionary, comparative, and developmental neuroscience the concept of the triune brain has been subject to criticism.⁴⁵

Humans are not at the mercy of mythical emotion circuits buried deep in the animalistic parts of our highly evolved brain: we are architects of our own experience. Click To Tweet

Let’s dig into some recent literature:

Rethinking the Lizard Brain: Meet Dr. Sara McKay

Illustration of lizard with a human brain Dr. Sara McKay, an Oxford University-educated neuroscientist, director of The Neuroscience Academy, and author of The Women’s Brain Book wrote in 2020:

“The lizard brain: the myth lurking in every coaching conversation.”³

In a wonderfully titled article “Your Brain Is Not an Onion With a Tiny Reptile Inside” – also from 2020 – Joseph Cesario et al noted three major problems with the triune brain model from the perspective of evolution.⁶

The Triune Brain Model implies evolution is a linear progression with one organism evolving into the next: lizards > mice > monkeys > humans
- This is wrong! Mammals did not evolve from reptiles. Mammals and reptiles share a common fish-like ancestor.
- “… the correct view of evolution is that animals radiated from common ancestors. Within these radiations, complex nervous systems and sophisticated cognitive abilities evolved independently many times.”⁷
Next, the theory is based on the belief that the brain evolved with more complex layers being added on top of pre-existing layers, like geological strata
- Wrong: Evolution consists of transforming existing parts
Finally, there’s an assumption that the cerebral cortex is unique to mammals
- Wrong again – all vertebrates – reptiles, fish, and birds – have a cerebral cortex (aka forebrain).

In Summary: the Triune Brain Theory is Bunkum, Senseless Talk, Nonsense

The triune model is oversimplified⁸ and inaccurate in terms of our brain activity, our emotions, and our behaviors,
Modern research and imaging capabilities show us that neural structures are NOT tied to specific cognitive functions.⁹ There is no hard-wired lizard-brain “fear circuit.”
Due to its longevity, the triune brain idea has also been called “one of the most successful and widespread errors in all of science.”¹⁰

Now WTF Do We Do?

If the model is wrong is it okay to still use it? Is it dangerous? Are there alternatives?

Emotions are not Pre-Wired – We Construct Them

While evolution has done quite a bit of heavy lifting, we do possess swift-acting threat-detection circuits. Various other, additional ingredients are processed by a network that builds consciously experienced feelings in the moment¹¹ based on what is going on around us. (Emotion Fingerprints or Emotion Populations? A Meta-Analytic Investigation of Autonomic Features of Emotion Categories)

In an easier-to-read title – 7½ Lessons About the Brain (2021) – Lisa Feldman Barrett shares the ingredients:

The physiological sensations we feel in our body (See Attitudes and Intentions)
The situation we’re in
The people we’re with
Our memories and personal experiences (See Archeology of Your Patterns)
The language we’ve learned to describe our conscious feelings¹²

And Maybe “That Gut” Feeling…

illustration of a stomach and a brain

…is more based on science than we realize. There’s a wonderful article that the BBC put out in 2023, “How gut bacteria are controlling your brain” – The article dives into our complex and remarkable biome.¹³ It turns out, according to this article, that these microbes that call our bodies their home don’t just help to keep our brains in prime working order by freeing up nutrients in our food. But they could also shape our very thoughts and behaviors.¹⁴

Feed Your Microbes (Not Your Lizard Brain)

There’s a wonderful TEDx talk that explores how the enteric nervous system goes beyond just processing the food we eat. For example, did you know that the “gut-brain” creates and stores 95% of our serotonin!¹⁵

Polyvagal Theory (Stephen Porges 1994)

Illustration of neurons and synapses There’s another theory that consciousness is distributed in the body, and it doesn’t exist in that three-pound lump of gray matter inside our skulls. It’s called the polyvagal theory.¹⁶ The theory states we have autonomous nervous system structures that are deeply involved:

Parasympathetic (rest, digest, repair)
- Ventral vagal complex – rest, digest, relax
- Dorsal vagal complex – immobilizaiton, dissociation, freeze
Sympathetic (fight-flight) – anxious, angry, aggressive, scared

These neural structures are not tied to specific cognitive functions but are impacted by a multitude of things: childhood development, and adult development.

Robert Kegan dives into adult development concepts:¹⁷

Impulsive Mind
Instrumental Mind
Socialized Mind
Self-Authoring Mind
Self-Transforming Mind (See Unhooking Your Buttons)

This whole range of embodied cognitive neuroscience honestly is way beyond my ken.

If you wanna dive in, see The Embodied Brain: Towards a Radical Embodied Cognitive Neuroscience

Does Any of This Really Matter?

“The most powerful person in the world is the storyteller. The storyteller sets the vision, values and agenda of an entire generation that is to come.” – Steve Jobs

I believe the stories we tell matter. All of us, as individuals, are part of a complex adaptive system that depends on social context. The language and metaphors we use impact our beliefs and our behaviors among our common systems: teams, clans, tribes, or value streams if you’re part of an agile release train.

Some wisdom from another Lisa Feldman book, How Emotions Are Made, (2018):

“Humans are not at the mercy of mythical emotion circuits buried deep in the animalistic parts of our highly evolved brain: we are architects of our own experience.”¹⁸

Instead of using neuro scientifically and evolutionarily incorrect analogies, we need to expand our palate.

Instead of blaming hard wiring or Darwin, maybe we realize that we – not some imaginary reptile inside our skulls – are in charge.

Explore Your Beliefs and Behaviors

Get started on the journey by:

Maintaining awareness of ourselves, our default behavior patterns, and intentions
Exploring ways to increase our ability to collaborate, problem-solve, and negotiate
Learning to build trust, overcome defensiveness, and seek constructive ways of getting things done

Here are some deeper dives: