Introduction. Brain neurobiology and evolution
The human brain’s evolution spans millions of years, building upon evolutionary older brain structures belonging to our animal ancestors.
The neurobiologist Paul MacLean demonstrated that the human brain retains functional structures from earlier mammals, even reptilian brains. This oldest reptilian brain structure, is the brainstem, located along the spinal cord extension.
The reptilian brain (R-complex)
The oldest region of the brain is the brainstem, located as an extension of the spinal cord. The brainstem corresponds to the reptilian brain. This structure of the brain contains nuclei, consisting of grey matter, which oversee essential life functions such as respiration and heart action.
The brainstem also houses the reticular system, responsible for sleep and wakefulness rhythms. The reptiles were not able to process cognitively past and future events. At this stage of evolution, emotions did not exist. In consequence the interactions within the brainstem were primarily instinctive and automatic.
The typical response patterns of a reptile and this brain region include:
• Winning and defending territory
• Dominating a rival
• Instinctively avoiding danger
• Mating.
The presence of this brain region in civilized humans signifies the existence of instincts and subjective emotions. By gaining control the reptilian brain can “shut down” the individual’s free will. Therefore, behaviours and feelings such as hatred, xenophobia, impulsive actions, as well as conformity, deception, and cunning, originate from this area.
The evolution of the mammalian brain
The brain region built upon the “R-complex” corresponds to the brain of a paleo-mammals. Structures belonging to this brain region include the limbic system along with the hypothalamus and the pituitary gland, which control and integrate the activities of all endocrine organs.
The hypothalamus and the pituitary gland operate based on the homeostatic principle: they monitor hormone levels, maintain the balance between hunger and satiety, oversee our sexual functions, fluid balance, and regulate the amount of sleep versus wakefulness.
At this stage of evolution, emotions like fear and anger emerged, along with associated environmental responses such as fight or flight. Such feelings as love and attachment are also related to this brain region.
This evolutionary leap brought about the following environmental reactions compared to reptilian behaviour:
1. Parenting and nurturing towards one’s own children
2. Audio-vocal communication between mother and child
3. Play
The most primitive form of vocalization in a mammal is the separation cry. It is the sounds produced by a young mammal when separated from its mother. The purpose of this cry is to prevent the non-viable offspring from being isolated from the mother.
Audio-vocal communication plays a significant role in the further development of a mammals. It facilitates the contact with other members of the group. At that stage of evolution mammals developed the play function. It is a practical form of training that enables the adult mammal’s survival ensuring the harmony within the group.
The function that determines mother-child interaction is anchored in the limbic system specifically in its thalamo-cingulate area. This applies to humans as well. In all mammals, including humans, the midbrain is the structure that monitors psychophysical efficiency and most adaptive reactions to the environment.
Brain evolution and the development of the neo-cortex
The higher psychic functions such as consciousness, “free will,” and “rationality” are anchored in the neo-mammalian brain, namely the neocortex. In the human brain, the neocortex is particularly developed and comprises 75% of the 10 to 12 billion neurons of the total brain structure.
As known, in humans, the left hemisphere of the brain is dominant. The two hemispheres are connected by the corpus callosum, a kind of rapid communication pathway between the two brain halves. The left dominant hemisphere (in right-handers) is responsible for our rational, empirical thinking and the use of language.
The latest evolutionary achievements of the human brain are the frontal areas of the cerebral cortex. These areas have given rise to the achievements of modern civilization, such as free choice, predicting consequences, and developing innovative solutions.
Furthermore, the frontal cortex also allows modern humans to exercise their free will and make decisions that deviate from the reptilian automatic response patterns.
The development of the frontal cortex, especially the left dominant hemisphere, is the material foundation for human civilization.
Brain evolution and the psychoanalytical theory
The midbrain, on the other hand, is the “material” foundation for Freud’s pleasure principle, housing reactions characterized by impulsivity and immediate gratification of desires. The neocortex, in turn, represents social adaptation, questioning reality, and constantly striving to control emotions originating from the midbrain.
Flor-Henry (1976) and Schwartz (1975) demonstrated that human emotional responses depend on the interaction between the limbic system and the parietal and frontal cortex of the left hemisphere. Flor-Henry found that the entire right-hemispheric, limbic, affective system is under the control of the left frontal cortex.