MacLean’s Trio Brain Theory proposes that the human species has evolved over time in terms of brain morphology, but instead of seeing it as a whole, unified process of change, she describes it as a process in which they have arisen new brain structures and independent with which each operates their own individual characteristics.
In this article, we’ll go over what exactly Paul MacLean’s Brain Trio Theory is and see why it isn’t valid for the scientific community.
What is MacLean’s Trio Brain Theory?
According to MacLean, in his book The Triune Brain in Evolution, our current brain is the sum of a layering process, Which appeared regularly over the millennia and settled on top of each other, but without the former ceasing to exist.
Thus, MacLean’s theory of the trio brain states that each of these structures has its own individual operating logic, and very different from that of the other layers, since the upper layers are the most evolved.
Let’s see below what these layers are according to the brain trio theory.
1. The reptilian brain
It would be the first of the three layers that exist in our brain, and represents the most basic instincts of the human species; hunger, sexual reproduction, sleep, instinct for survival and struggle.
This brain would be made up of the first structures to appear, which are the basal ganglia, the brainstem and the cerebellum. All these structures they are located at the bottom of our brain.
Proponents of this theory claim that the reptilian brain contains a large amount of information in its individual memory; this information would be shaped by ancestral rites and esoteric beliefs without any scientific basis.
2. The limbic system
This second structure, or second brain, according to the theory, would be the one in charge of all the sensations we experience when we carry out an activity. For example, when we eat something we really like, when we have sex with someone we love, or when we enjoy a beautiful landscape.
These emotions are in charge of the limbic system, which, according to the Trinitarian Brain Theory, becomes the next nervous system structure to evolve after the appearance of the reptilian brain.
This layer is made up of the cerebral amygdala, septum, hypothalamus, cingulate cortex, and hippocampus.
3. The neo-crust
This layer is the most recent in human evolution, it is also known as the modern brain. It is exclusive to mammals.
the neo-crust he is in charge of everything related to abstract thinking, logical and rational thinking, Besides the complex communication processes we use to communicate in modern society.
It is made up of the cerebral cortex, which is made up of gray matter, where there are a large number of neurons in constant connection with each other.
Considering what has been seen so far, it can be said that MacLean’s Brain Trio Theory assumes that our current brain is nothing more than a summation process between individual layers that has arisen in our species making us more and more rational.
Each of these layers, as we have already seen, has its own characteristics; no matter how much the functions of one have to do with the functions of another structure, these work on their own. In other words, neither layer has control over the other, but they could, for example, make the subject aware of his desires and thus make them channel correctly.
This theory has not been well received in the world of the scientific community, and most specialists in the field of neuroscience have expressed their disapproval of this assumption. Let’s see why.
What does science say?
Brain theory triumphs for neuroscientists it has too many inconsistencies in its approaches to be considered valid.
We now know that the specific functions that this theory gives to the structures mentioned are not properly those of the most evolved vertebrates, that is to say that in other species also appear similar behaviors.
For example, birds, without having the limbic system, have a strong protective instinct towards their reproduction, which is a characteristic attributed to the second brain (limbic system) according to MacLean’s theory.
In addition, there are intelligent mollusks like octopus, the brain has nothing to do with that of vertebrates, capable of having social behaviors and adjusted to rationality.
More recent findings also overturn the theory that the neo-crust emerged as the last stage in the evolution of the modern mammal. Today it is known that the first signs of gray matter in the upper areas of the brain they were found in primitive mammals.
That is to say, that these structures did not appear in ascending order as he raises the author of the theory of the triú brain, but all already came to exist in the same brain, which evolved in a general way, and did not not gone.
Moreover, the way evolution works does not consist of an accumulation of traits that do not influence each other. In other words, the changes caused by the mutations that are reflected in the bullet holes in the brain structure do not occur individually, but in interaction with the rest, so that a part that was previously specialized in certain mental processes can becoming responsible for others another new set of nerve cells appears.
- Gardner, R .; Cory, GA (2002). Paul MacLean’s Evolutionary Neuroethology: Convergences and Borders. New York: Praeger.
- Lambert, KG (2003). The Life and Career of Paul MacLean: A Journey Towards Neurobiological and Social Harmony. Physiology and behavior. 79 (3). Elsevier: pages 343 to 349.
- Velásquez Burgos, BM, Carrer, MG and Remolina De Cleves, N. (2006). Neuroscientific theories of learning and their implication in the construction of knowledge of university students. Tabula Rasa, (5): p. 229 – 245.