"The reptilian brain forms a primitive brain that is sensitive to fear and has a desire for desired rewards. It shows the mammalian brain surrounding it, and beyond that, the prefrontal brain that only humans possess. 〈Eden's Dragon〉 beautifully depicts the emergence and evolution of human intelligence through evolutionary research results." (Source: Jeong Jae-seung, Twelve Steps, Across, 2018)
〈Eden's Dragon〉 is a book written by astronomer Carl Sagan, published in 1977. This book introduces the cosmic calendar, which later appears multiple times in 〈Cosmos〉. In the cosmic calendar, humans appear at 10:24 PM on the last night of the year. The story of the very young brain possessed by humans compared to the incredibly ancient universe unfolds in 〈Eden's Dragon〉.
In the book 〈Twelve Steps〉, Jeong Jae-seung, the head of the Brain and Cognitive Sciences Department at KAIST, recommends it as follows. "The human brain and mind are products of the grand material evolution that began with the Big Bang, and his statement that the brain and mind are not governed by a single principle but are a complex process created by various impulses and logics with evolutionary origins seems to still hold true." (Source: Kyunghyang Shinmun, The Brain of Young Humanity Living in an Old Universe, 2006.09.28.)
From Paul MacLean to Carl Sagan to Jeong Jae-seung, the Spread in Korea
The origin of the 'reptilian brain' is neurologist Paul MacLean. In his 1964 paper titled 'Man and His Animal Brains,' he argued as follows.
"One of these brains is fundamentally similar to that of reptiles, the second brain is inherited from lower mammals, and the third has developed in the late stages of evolution, allowing humans to exist as humans."
This claim was not respected in the neuroscience community at the time. However, it spread widely through popular science writings. In the 1960s, Arthur Koestler's 〈The Ghost in the Machine〉, which summarized this research and added sensational elements, became a bestseller. In the 1970s, Sagan took over the baton and won the Pulitzer Prize in 1978 for 〈Eden's Dragon〉.
Sagan connects the reptilian brain to the story of the Garden of Eden in the Old Testament. He asks, "Could the metaphor of the serpent imply that the aggressive and conventional reptilian part of our brain was used in the process of further evolution of the neocortex?"
His imagination leads to fear of dragons. Sagan states, "The irreconcilable strong hostility between humans and dragons is most strongly manifested in Western culture," but he also claims, "Such hostility is not only present in the West but is a global phenomenon." He even supports his speculation with the question, "Is it just a coincidence that the universally made 'shh' sound to quiet someone or draw attention is similar to the hissing sound of reptiles?"
The claim that the world universally feared dragons distorts the facts. In the East, including China, dragons were auspicious beings along with phoenixes and qilins. If that were not the case, how could dragons be embroidered on the conquering robes worn by kings?
Excessive Imagination Based on Fear of Dragons
After assuming human fear of the imaginary being dragon, he ponders the basis of this imagination as follows.
"The most recent dinosaur fossils are estimated to be about 60 million years old. The family to which humans belong (but not the genus Homo) has a history of about tens of millions of years. So, is it not possible that creatures similar to humans directly encountered a Tyrannosaurus?"
This is the imagination that there may be events from 60 million years ago, which is many times longer than the period humans have existed since becoming human. Since this cannot be verified, it cannot become a scientific hypothesis.
The 'reptilian brain' proposed by MacLean has long been discarded in the neuroscience community. Oxford anatomist Ray Guillery commented that MacLean's claim is a 'neuroscientific myth.' Scientists explain that there is no independent layer in the human brain that has continued from the reptilian era. They also state that the human brain is not a structure added sequentially but a network that has evolved together. In short, impulses and reason are not handled by different brains but operate with multiple circuits involved simultaneously.
The 〈Eden's Dragon〉, which has been developed and inherited from MacLean's ideas, has received sharp criticism from Matthew Cobb, a professor in the Department of Life Sciences at the University of Manchester. Cobb harshly criticized that in the 〈History of Neuroscience〉, "Like Koestler, Sagan mixed a huge amount of nonsensical psychoanalysis and poorly understood anthropology with some fragments of scientific facts, and then unraveled that mixture with excessive speculation."
The role that Professor Jeong Jae-seung played in the process of the transmission and spread of the 'reptilian brain' is self-contradictory. As previously introduced, Professor Jeong strongly recommended 〈Eden's Dragon〉 in print media contributions and lectures. However, he wrote a recommendation for the 〈History of Neuroscience〉, which harshly criticized this book. He called it "an incredibly interesting history book on brain science!"
Meanwhile, Professor Jeong Jae-seung did not acknowledge the 'reptilian brain.' He added the caveat that it is "a theory not commonly used these days."
Metaphorical Concepts Are Redundant; Analyzing Behavior Is Useful
Physicist Richard Feynman actively communicated with the public on the subject of scientific inquiry. Many videos of him can be found on YouTube. Among them, there is a segment where he explains 'inertia.' As a child, he played with a toy train with marbles placed horizontally. When he pushed the train quickly, the marbles rolled back. When he explained this phenomenon to his father as the result of "inertia," his father replied, "Just naming a phenomenon doesn't mean you understand it."
The attempt to explain the impulsive part of human thought with the concept of the 'reptilian brain' is not different from the approach of young Feynman. Moreover, the reptilian brain has been revealed to be a fiction through brain science research.
Understanding human thought is better served by behavioral economics than by metaphorical concepts about the brain. I recommend Nobel Prize-winning psychologist Daniel Kahneman's 〈Thinking, Fast and Slow〉.
