The oldest of the three brains is situated in the core layer. The most recent is the outermost layer. The intermediate is the middle layer.
The
oldest of the three is the reptilian,
primitive or
archipallium brain, which MacLean also calls the “R-complex”. It
corresponds to the brain stem (midbrain, pons and medulla) and the
cerebellum. It is responsible for the self-preservation processes, like
respiration, heart beating and sleep, as well as for the unchangeable
rituals of approaching, attacking, flight and mating. None of those
processes require conscious control but they are essential to the
animal’s life as can be shown by the fact that the reptilian brain
never stops working not even during deep sleep. The reptilian brain
never changes and never learns from experience. It is almost identical
to the brain of present day reptiles, having been present in the
reptiles that preceded the first mammals about 240 million years ago.
The reptilian brain responds to the mechanical, purely instinctive
behavior.
Most mammals share with us the paleomammalian
(old
mammalian) brain, which corresponds to the limbic system, the middle
part of the brain. MacLean believes that it appeared after the
reptilian brain and was added to it at about 60 million years ago.
Primitive mammals had a brain that
was basically the reptilian brain plus the limbic system. The
paleomammalian brain contains the hypothalamus, the thalamus, the
hippocampus and the amygdala, which are considered responsible for
emotions and emotional
instincts like behaviors associated to feeding, competition and sex.
Such emotions are important to the survival of the animal and its
species.
The paleomammalian brain is able to learn since it keeps memories of
emotions
that result from experiences where the animal felt pleasure or pain
with
more or less intensity. The paleomammalian brain is responsible for the
emotional behavior. 
The
cerebrum, neocortex, cortex or neopalium is
the main
brain
of the primates, which were among the latest mammals to appear. It
represents about five-sixths of the human brain, having evolved along
the last million years. MacLean calls it the neomammalian (new mammal)
brain. All mammals have neocortex but it is particularly important only
in primates and cetaceans. The neomammalian brain is responsible for
the noblest cognitive functions, like language and reasoning. The
neocortex corresponds to the rational behavior.As we have seen, all three brains act together to produce the behavior of the mammals and of man in particular, which, according to circumstances, can be predominately mechanical, emotional or rational.
In order to better understand to what extent MacLean’s theory says about the soul’s evolution, we must have in mind the organizing function of the perispirit (subtle body). This subtle body we have, which, added to the soul, from which it never moves apart, form the Spirit, functions as a wonderful transpersonal memory keeping record of all the events lived by the being in its innumerous physical lives and of the effects of those events according to the Law of Causality.
Being so, if we find a reptilian brain in the physical brain that means that there is a reptilian subtle brain in the perispirit serving as its model. Furthermore, that reptilian subtle brain present in the perispirit is the indelible record of the soul’s history.
Following this line of thought we could ask, if one is to accept the hypothesis of man’s evolution coming from a lower realm species, why shouldn’t the record of other species previous to a reptile be present in the human brain. The answer to that question can be found, to our view, in the thesis presented by André Luiz and developed by Jorge Andréa, according to which individuality is defined when the first cells of the pineal gland start to show up in an animal.
Many fish, all reptiles, birds and mammals that live today have a pineal gland. Such however may have not been true 240 million years ago in the Mezozoic Era, when scientists believe reptiles originated the first mammals. The Tuatara is a small reptile living nowadays in some islands north of New Zealand, which has a third eye linked to its primitive pineal gland. The Tuatara is a living fossil belonging to a family that existed during the Mezozoic Era, making it possible for us to infer, if we use the thesis proposed by Jorge Andréa, that the reptiles from which mammals originated had a pineal gland about as primitive as it has. Furthermore, it allows us to conclude that no species in the evolution history of those reptiles before they became reptiles had a pineal gland at all.
Before the pineal gland was present in the animal, as Jorge Andréa explains, the soul-group-of-the-species dominated over the incipient individual vortexes. So, it is natural that events previous to the moment the individuality was established had to be recorded in the organizing model of the soul-group of the species from which the individuality would originate. This explains why there is no record of them in the present triune brain.
As we have seen, the model proposed by MacLean is rather elegant and useful, serving to explain, in a clear and didactic way, how human evolution occurred, from the most primitive instincts of an autonomous life to the use of mind’s noblest functions, reason and consciousness, passing by the intermediate stage of learning in order to adapt to the environment. Another interesting characteristic of MacLean’s model is that it allows us to imagine the appearance of new layers in our brain, as we further climb the steps that lead us to perfection.
When we reach the next stage, as occurred at previous transitions, the brain we now call neomammalian no longer will be responsible for mind’s noblest functions. Such noble functions, which will certainly no longer be the same that we call “noble” nowadays, will be processed in the new layers that will appear.
That view seems compatible with the fact that highly evolved Spirits are incapable of doing bad deeds. Maybe the fact that they only do good deeds only reflects what has come to be an instinctive behavior.
Unfortunately Science never bothered to examine the brain of saints, dedicating only to study the brains of important politicians, artists or scientists. Would examining the brain of Saint Theresa D’Avilla, the Mahatma Ghandi or Chico Xavier have revealed the existence of a tetraune brain? Would it have revealed a triune brain having 7 and not 6 layers in its neocortex? Those are questions whose answers we still ignore.
BIBLIOGRAPHY
ANDRÉA DOS SANTOS, Jorge. Impulsos Criativos da Evolução (Evolution’s Creative Drives). Rio de Janeiro: Societo Lorenz, 1995.
DO AMARAL, Júlio Rocha, MD, and MARTINS E OLIVEIRA, Jorge MD, PhD. Limbic System: The Center of Emotions. January 2003.
URL: http://www.epub.org.br/cm/n05/mente/limbic_i.htm.
MILLER, Richard Alan. The Biological Function of the Third Eye. February 2003.
URL: http://www.bleehoney.org/ThirdEye.htm.
SCARUFFI, Piero. Book review of Paul MacLean’s The Triune Brain in Evolution. January 2003.
URL: http://www.thymos.com/mind/maclean.html.
Triune Brain Theory: Three Brains in One. February 2003.
URL: http://www.mareshbrainsatwork.com/B2B/index.htm.
Tuatara – The World’s Most Unique Reptile. February 2003.
URL: http://www.bigjude.com/Tuatara.html.
XAVIER, Francisco Cândido, and VIEIRA, Waldo. Evolução e Cérebro. In: Evolução em Dois Mundos (Evolution and the Brain. In Evolution in two Worlds). Dictated by Spirit André Luiz. Rio de Janeiro: FEB, 1993.
ZIMERMANN, Zalmino. Perispírito (Perispirit). Campinas: CEAK, 2000.