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These are excerpts and elaborations from my book "The Nature of Consciousness"
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The Three Stages of Brain
Evolution The US developmental
psychologist Stephen Porgescharacterized the evolution of
consciousness as a transition from a state of being acted upon by the world to
a state of acting upon the world. Consciousness originated when the brain
evolved from the reptilian structure to the mammalian structure (using Paul
MacLean's model for the evolution of the brain). The brain of a reptile
(which de facto means the brainstem and the hypothalamus) is not active, but
simply reactive: it reacts to food, light, temperature. The reptilian brain increases or decreases
metabolism based on the bodys needs. Matter prevails over mind. In a mammal, instead, the
brainstem and the hypothalamus command adjustments so that body temperature and
metabolism are kept stable. This phenomenon enables the brain to dedicate
energies to other functions. The brain of a mammal is capable of acting:
mammals explore their environment looking for what they need. Mind prevails
over matter. The same argument can be made
from an energetic perspective, which is reflected in the differences between
the reptilian and mammalian cardiac systems. In the highly competitive world of
mammals, it is necessary for the body to increase the production of energy to
deal with preys and predators (hunt or run). So it is no surprise that mammals
have metabolic demands four to five times that of reptiles, which makes
reptiles more prone to passive feeding strategies, whereas mammals can actively
hunt and graze and adapt to changing environments. The reptilian brain is
designed to use food. The mammalian brain is designed to look for food. The structures in mammals
(i.e., facial muscles, larynx) that express emotion (facial expression,
vocalization) were evolution of anatomical systems of the reptiles. The
resulting organization of the brainstem in mammalians fostered brain functions
of attention, motion, emotion, and communication. The development of the
cortex enabled the mammalian brain to communicate emotions. Then it was just a
matter of time before language and conscious thought emerged. Back to the beginning of the chapter "A History of Consciousness" | Back to the index of all chapters |
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