Humans Do Not Have an Evolved “Lizard Brain”
The notion that the base of our
brain evolved from a lizard
brain is now fully debunked
The Triune Brain: A Dangerous Evolutionary Blunder
A Review of Evolution’s Dangerous Ideas
by Jerry Bergman, PhD
Introduction
One influential idea in evolutionary neuroscience held that, because of our animal ancestry, humans inherited the brains of “three animals: a primitive crocodile, a panicky mouse, and a pragmatic human being. … These three metaphorical animals are thought to occupy the inside of your head, fighting for control over your body…. On top of this ancestral brain, we are said to have evolved a second brain, full of emotions, shared with mammals like mice and horses.”[1]
The human brain was, in fact, interpreted and taught by the triune brain model, also called the lizard brain theory, to be three brains: a lizard brain for survival, a limbic brain for emotions, and a newly evolved human brain for rationality. According to this model, the human brain consists of three evolutionary layers: a reptilian brain responsible for survival instincts, a limbic brain that governs emotions, and a recently evolved neocortex responsible for rational thought of modern man.
The triune brain model “was a once-popular model of the evolution of the vertebrate forebrain and behavior, proposed by the American physician and neuroscientist Paul D. MacLean in the 1960s.”[2] Furthermore, MacLean “was one of the trailblazers of neuroscience whose work in the 1940s and ‘50s provides many of the insights into the functions of the brain upon which today’s neuroscientists build.”[3]
Due to MacLean’s influence, the triune brain model was widely accepted for decades. It even became a standard part of psychology and neuroscience education. One review of 20 introductory psychology textbooks found that although most discussed brain evolution, nearly all repeated the erroneous “reptile brain” concept.[4]
As one review concluded, the triune brain model, which describes the mammalian brain as consisting of three functionally distinct evolutionary layers, “has become a widely used way of thinking about the overall functional organization of the brain.”[5]
The Popular Scientific Triune Brain Model Now Falsified
Carl Sagan first encountered Paul D. MacLean’s theory at a 1971 scientific conference, where MacLean presented the triune brain model. Sagan later corresponded with MacLean and was intrigued by the idea of a “lizard brain,” “mammalian brain,” and “human brain” coexisting within the human brain. He even suggested to MacLean that, if the model were evolutionarily correct, it might be possible to reveal the primitive “lizard brain” through the use of an appropriate mind-altering drug.
Carl Sagan by model of the Viking lander that did NOT find life on Mars.
Sagan popularized the triune brain model in his 1977 Pulitzer Prize-winning book, The Dragons of Eden. The reptile brain idea was then picked up by Sagan’s millions of readers, and seeped into mainstream culture. Sagan used the triune brain evolutionary model to explain human behavior, arguing that our rational minds are built over or upon our ancient “reptilian” and primitive “mammalian” brain layers.[6] Sagan also used the evolutionary model to explain human behavior, arguing that our rational minds are built upon more ancient reptilian and mammalian brain systems which explains much irrational human behavior.
One of the most harmful ideas associated with the early evolutionary interpretation of brain function was the movement that culminated in prefrontal lobotomy, which Reiner described as “the blight that was pre-frontal lobotomy.” This tragic chapter resulted in an estimated 50,000 lobotomies in the United States alone, with reported mortality rates ranging from about 3% to 15%, depending on the practitioner. Up to one-fourth of patients experienced no improvement, while most survivors suffered permanent personality, intellectual, and cognitive impairments.[7]
The Triune Brain Theory Firmly Rejected
The triune brain model, once widely accepted, has since been decisively rejected by modern neuroscience.[8] As neuroscientist Lisa Feldman Barrett writes, “You Have One Brain (Not Three).” As stated by neuroscientist Lisa Barrett, the fact is “You Have One Brain (Not Three).”[9] Likewise, neuroscientist Joseph Cesario and his colleagues concluded, contrary to what the evolutionary triune brain model taught for decades, “Your Brain Is Not an Onion With a Tiny Reptile Inside”.[10] As Anton Reiner, Professor of Anatomy and Neurobiology at the Universite of Tennessee, explained, one of the model’s fundamental problems was its evolutionary foundation:
… neuroscience research has undergone tremendous growth, and knowledge about the brain, its functions, and its evolution has been greatly extended. As new information accumulated, it became clear that the older, simpler ideas about brain evolution and function upon which the triune brain idea is based are fundamentally wrong.[11]
Learn about other blunders made by evolutionists in this book by Dr Bergman. Click to order.
Why did this “fundamentally wrong” idea become so widespread and accepted? One reason was its compatibility with evolutionary thinking.[12] The notion that evolution had built a newer brain on top of an older one—and that our primitive instincts could therefore be blamed on an inherited reptilian brain—provided an appealingly simple explanation of human behavior. Its simplicity helped make the model attractive to both the public and many scientists.
One analysis of the lizard brain theory concluded that one of MacLean’s “very critical misjudgments” was his “sweeping acceptance of Haeckel’s idea that ontogeny recapitulated phylogeny.”[13] This doctrine held that an organism’s development from a single cell to adulthood (its ontogeny) replays the evolutionary history of its species (its phylogeny). This concept has long since been rejected and is widely regarded as one of the major mistakes in the history of biology.[14] The problems with the doctrine were further highlighted by the extensive documentation showing that Ernst Haeckel’s embryo drawings had been purposefully altered in misleading ways.[15]
New Ideas
The triune brain model, once widely accepted in neuroscience, is now regarded as an embarrassing and fundamentally incorrect account of brain evolution and organization. Modern neuroscience has shown that this evolutionary model greatly underestimated the complexity of both human and animal brains. It is another example of an influential evolutionary theory (or model) that gained widespread acceptance before research demonstrated that it was fundamentally mistaken.
Changing the Narrative but Not the Foundation
Although Darwinians have ceased accepting the lizard brain theory, they have not by any means rejected the idea that the brain evolved.
The Lizard brain has been relaced by the idea that brain evolution is much more complex and integrated then once believed. As explained by Nabil Imam, an assistant professor at Georgia Tech’s Institute for Neuroscience, Neurotechnology, and Society the brain, as is also true of the rest of the body, is much more complicated than previously assumed:
“The limbic system, sometimes called the ‘reptilian brain,’ controls emotion broadly speaking — but it also has other components with distinct functions. The system has separate regions for memory, smell, and navigation in addition to emotional regulation… The limbic system behaves not as a loose collection of functions, but as a unified network that expands and contracts as a group across evolution [when different animals are compared].”[16]
Professor Imam added that
“it comes down to how these different parts of the brain are wired before birth. In the neocortex, neural circuits are organized as spatial maps. Areas that process touch in nearby parts of your body, like your index finger and thumb, are physically close to each other in the brain. The same is true for sight and sound.”[17]
This new insight replaces the “new” brain layered over an “ancient” one — or even a logical brain versus an emotional one. The old view fit very well into evolution, which is one reason for its wide acceptance.
In contrast to the old lizard brain idea, the new understanding of the human brain as a unified network supports creationism.
Editor note: Expanding on that last sentence, it should be obvious that any “unified network” that is “wired before birth” with “memory, smell, and navigation in addition to emotional regulation” defies Darwinian theory with its blind, unguided processes of mutation and selection. How do these scientists deal with the appearance of a “system of systems” that wires itself from before birth? What you find by reading the press release is Darwinian cheating. They treat natural selection like an agent that optimizes each brain. For example,
By studying the architecture of both biological and artificial brains, Imam’s team found that brain evolution is a strategic allocation of limited real estate. They propose a computational tug-of-war between two fundamentally different types of internal wiring — ones established even before birth.
This is the fallacy of personification. “Who” is looking at the real estate and strategically allocation its resources? Are different brain regions “competing” for real estate on purpose? Darwinism has no guiding hand, and early brains were not capable of conscious rational thought to compete or to recognize a reward. Stuff just happens.
This quote is followed by more fallacies, namely bluffing combined with sidestepping:
This new understanding not only helps resolve a longstanding mystery in brain evolution but could also help us design more efficient AI systems.
Darwinism has nothing to do with designing, efficiency, or AI. The statement bluffs that the “new understanding” is actually a victory for evolutionary theory! Look how useful it is: Darwinism can help us design more efficient AI systems! Balderdash. These evolutionary scientists should be apologizing for misleading the public for over 50 years by repeating a hare-brained notion of a three-layered pancake brain that evolved by sheer dumb luck. They should apologize to the many who were given frontal lobotomies from this evolutionary story, now debunked. As usual, the coveted “understanding” promised by evolution never arrives.
References
[1] Jonathan Jarry, “You do not have a lizard brain,” Office for Science and Society at McGill University, https://www.mcgill.ca/oss/article/critical-thinking-history-general-science/you-do-not-have-lizard-brain, 2 July 2026.
[2] “Triune brain,” https://en.wikipedia.org/wiki/Triune_brain, 2026.
[3] Reiner, A., Book Review of MacLean, Paul D., An Explanation of Behavior: The Triune Brain in Evolution, Chapter XXIV: “Role in Paleocerebral Functions,” New York, NY: Plenum, Science 250(4978):303–305, p. 303, 12 October 1990.
[4] Jarry, 2026.
[5] Baars, Bernard J., and Nicole M. Gage, Cognition, Brain, and Consciousness, Chapter 13: Emotion. Elsevier New York, NY: Elsevier, p. 214, 2010.
[6] Bergman, Jerry., “Half-truthing the history of Lobotomy. Lobotomy: telling only half of the story by ignoring the major contribution of Darwinism, https://crev.info/2021/11/lobotomy-half-truths/, 5 November 2021.
[7] Bergman, Jerry, Chapter 3: “The Darwinian Mental Health Holocaust: Frontal Lobotomies,” pp. 67-88, in Evolution’s Dangerous Ideas: Eugenics, Lobotomies, Using X-Rays to Speed Up Evolution, and Other Dangerous Ideas Inspired by Darwinism, Cántaro Institute, Jordon Station, ON: Cántaro Publications, 2024.
[8] Steffen, Patrick R.; Hedges, Dawson; and Matheson, Rebekka, “The brain is adaptive not triune: How the brain responds to threat, challenge, and change,” Frontiers in Psychiatry 13:802606, doi:10.3389/fpsyt.2022.802606, PMC 9010774, 1 April 2022.
[9] Barrett, Lisa Feldman, “You have one brain (not three), Seven and a half lessons about the brain,” Boston, MA: Houghton Mifflin Harcourt, pp. 13–28, ISBN 978-0-358-15714-4. OCLC 1129098750, 2020.
[10] Cesario, Joseph; Johnson, David J.; Eisthen, Heather L., “Your brain is not an onion with a tiny reptile inside,” Current Directions in Psychological Science 29(3):255–260, June 2020.
[11] Reiner, 1990, p. 304.
[12] Butler, A.B., “Triune brain concept: A comparative evolutionary perspective,” Encyclopedia of Neuroscience, pp. 1185–1193, doi:10.1016/B978-008045046-9.00984-0, 2009.
[13] Reiner, 1990, p. 305.
[14] Hopwood, Nick, Haeckel’s Embryos: Images, Evolution, and Fraud, Chicago, IL: The University of Chicago Press, 2015.
[15] Bergman, Jerry, “The definitive work on a sordid affair,” Review of Haeckel’s Embryos: Images, Evolution, and Fraud by Nick Hopwood, Journal of Creation 29(3):15-18, 2016.
[16] The Myth of the ‘Lizard Brain’ and the Real Trade-Off Inside Your Mind, Georgia Tech press release. https://research.gatech.edu/myth-lizard-brain-and-real-trade-inside-your-mind. June 29, 2026.
[17] The Myth of the ‘Lizard Brain’.
Dr. Jerry Bergman has taught biology, genetics, chemistry, biochemistry, anthropology, geology, and microbiology for over 40 years at several colleges and universities including Bowling Green State University, Medical College of Ohio where he was a research associate in experimental pathology, and The University of Toledo. He is a graduate of the Medical College of Ohio, Wayne State University in Detroit, the University of Toledo, and Bowling Green State University. He has over 1,900 publications in 14 languages and 40 books and monographs. His books and textbooks that include chapters that he authored are in over 1,800 college libraries in 27 countries. So far over 80,000 copies of the 60 books and monographs that he has authored or co-authored are in print. For more articles by Dr Bergman, see his Author Profile.