link: brain evolution

                                                                        BRAIN EVOLUTION

 

The evolution of the human species is concurrent with the evolution of the human brain. The mammalian brain can be traced back at least one hundred and fifty million years. Its greatest development was achieved in the past three million years. The full evolution of the human brain  came after the early hominids acquired upright posture which allowed them to make and use tools. It is subsequent to these developments that there was a sharp an explosion in brain size... increase in cranial capacity and in size of the cerebral cortex. Brain development culminated about two hundred and fifty thousand years ago in the evolution of the true human brain of homo sapiens and since then there has been further rapid brain development. (language...)

"As a product of millions of years of evolution through natural selection, the specialized brain functions have ensured the survival of the human species. The functions of the human brain are the natural outcome of millions of years of evolutionary process through natural selection. The mental functions of learning and memory are natural outcomes of the human evolutionary process of behavioural adaptation. In the course of human evolution, survival of the human species has depended on behavioural adaptation. Human adaptive behaviour has depended on brain development. The evolution of the human species is concurrent with the evolution of the human brain. This is in contrast to the evolution of other organisms whose survival and adaptation have depended on the development and specialization of various other organs and other forms of instinctive behaviour". (Eric R. Kandel and Robert D. Hawkins "The Biological Basis of Learning and Individuality" Scientific American September 1992 79-86)

triune brain: reptilian brain or 'R-complex'... mammalian brain or limbic system'... cerebral cortex...

early hominids: bipedalism allows for tool use and increase in brain growth...    

hominids and homo sapiens sapiens...

 survival value of brain as 'meaning maker'...

implications for education...

Evolution over 400 million years  The characteristic functions of the human brain are the natural outcome of millions of years of evolutionary process through natural selection. The main structures found in the human brain are present in the brains of all other vertebrates. The basic plan of the brain may have been laid down as long as 400 million years ago with the appearance of sharks in the Devonian period. 

The brain is three-layered or 'triune'  Each of the three brain layers represents an evolutionary stratum that has formed upon the older layer before it (like an archeological city).

In the 1960's neurologist Dr. Paul MacLean (The Triune Brain in Evolution) - director of the Laboratory for Brain Evolution and Behaviour of the National Institute of Mental Health - was a philosopher who 'converted'  to the study of science and medecine when he took a course in the philosophy of science. MacClean expanded on the work of James Papez and conducted his research on the assumption that the behavior of animals is relevant to the understanding of human behaviour. His study of the evolutionary development of the nervous system led to a description of the human brain in terms of three major layers  with distinctive functions... three 'brains' which were established successively in the course of human evolution. Hence the term 'triune brain'. The oldest layer is the known as the 'reptilian system' or 'R-complex' because it makes up the entire brain mass in reptiles; the second oldest is known as the 'mammalian brain' because it developed with the evolution of mammals; and the third and most recent is the 'neocortex'. Each of the three brains has its own way of perceiving and responding to the environment and each can become dominant depending on the circumstances. Although each layer has a separate function, all three layers interact. The interaction of the three brain layers forms the biological basis for the interaction of concepts and emotions which together make up human behaviour.

Reptilian system or 'R-complex' The R-complex the most primitive of the three is also known as the 'archipallium brain' or 'root brain'. It consists largely of the 'brain stem', the 'basal ganglia', the 'reticular activating system' and the 'midbrain'. Functions of the R-complex are related to physical survival and body maintenance - digestion, reproduction, circulation, breathing, response to stress and so on. The functioning of the R-complex is activated when the organism perceives threat and the needs for survival and safety predominate. Functions related to the instinctive behaviour patterns self-preservation include automatic behaviours of 'territorial instincts' or 'territoriality', social dominance and ritualism, status maintenance, deception, tendency to follow precedent and resistance to change, awe for authority, social 'pecking order' behaviour, compulsiveness, prejudice . 

  Mammalian brain or 'limbic system' As the second layer of the human brain, the mammalian brain which occupies the lower fifth of the human brain is also known as the 'paleomammalian brain'. The paleomammalian brain consists of a series of brain structures around the brainstem which contains the R-Complex... the 'hypothalamus' is connected to its other components and their functions - 'hippocampus' (spatial memory), 'amygdala' (associationof events with emotion), 'mammillary body', 'anterior thalamus', 'cingulate cortex'. Together they form a cap or 'limbus' (Latin for shell or girdle , 'forming a border around' or 'ring') Hence 'limbic system' or 'limbic brain'. The limbic brain, like the R-complex, is concerned primarily with self-preservation and species-preservation and controls the autonomic nervous system. The limbic system functions in primal activities related to defense ('fight or flight' fear response), food and sex as well as activities related to the expression of emotions and feelings (fear and protection) linked to the attachment and care of offspring. These become increasingly complex since the limbic system interacts with the thinking part of the brain - the 'cerebral cortex'. Of particular significance is the role of the limbic system in sense perception and memory. Sensory input is monitored and converted into appropriate modes for processing and then directed to the appropriate memory storage system. Neurochemicals in the limbic system are instrumental in the transfer of memory from short-term to long-term storage which takes thirty seconds.

Cerebral cortex or 'neo-cortex': neo-mammalian brain (sense of self... 'consciousness'... 'conscience'). The third layer occupies five sixths of the brain and is known as the 'neomammalian brain', 'neopallium brain', the 'neocortex' or the  'cerebral cortex'. The cerebral cortex is the latest evolutionary development of the brain... the distinctively primate and human layer. The cerebral cortex is involved with most mental activity, including spatial and mathematical thinking, meditating, dreaming, remembering, processing and decoding of sensory information. The cortex is two millimeters in thickness and covers the two 'cerebral hemispheres'. The numerous morphological subdivisions are based on the numerous neurological functions - seat of language, speech, thought and sensory processing and so on. These include motor-control and some associative events. Sensory-receiving areas and motor-control areas are well-defined. Areas involved with associative events are less well-defined. The cerebral cortex is considered to be the structural and functional 'interface' between input of environmental stimuli and brain output.

According to  the three layers of the human brain operate like 'three interconnected biological computers, each with its own special intelligence, its own subjectivity, its own sense of time and space and its own memory' (McLean) Each is connected by nerves to the other two. The assumption that the neocortex dominates the R-complex and the limbic system is annulled by the finding that the mental functions of the neocortex can be hijacked by the functions of the other two brain layers.  

 Increase in brain size occurred after the hominid ancestors... 'early hominids'... stood upright three to four million years ago when the brain was still small... upright posture or 'bipedalism' followed The prehominid ancestors of homo sapiens - Dryopithecus and Ramapithecus - appeared about 20 million years ago. They had brains which were no bigger than monkey brains. For the next 17million years or so, practically no change in brain size occurred. About 3 million years ago the 'australopithecine hominids' appeared rather abruptly, with larger brains with 'cranial capacity' of about 500cc. The evolution of the hominid brain to its present size is a relatively recent phenomenon... the greatest brain development occurred within the last 3 million years.

Data Studies show that brain growth (evolution of human intelligence) increase in brain size... correlates withfollowed upright posture or 'bipedalism' providing the conditions for tool use...

The explosion in brain size... cerebral cortex... sharp increase in the cranial capacity... brain size increased... after early humans started to make tools... tool use followed upright posture.The complete evolution of the human brain required that the early hominids use tools and tool use necessitated that they have upright posture. With upright posture, the forefeet were relieved of the function of carrying the weight of the body and they evolved as hands with 'opposable thumb' and 'prehensile fingers' capable of subtle and accurate movements... hands were free to pick up stones and sticks, manipulate objects and eventually make tools. Tool making was the first 'applied science'. The simultaneous development of a complicated nervous system made it possible to control the movements of the hands in response to impressions received by the eyes.

"...the full evolution of human intelligence required for its movement the presence of bipedalism and tool use in early hominids. It is subsequent to these developments that we find a sharp increase in man's cranial capacity and in the size of his cerebral cortex." (Jerome Bruner. The Relevance of Education New York: W.W. Norton & Co., Inc.1971)

  "Brain growth followed upright posture. With upright posture, the hands were free to pick up stones and sticks, make tools etc. Explosion in brain size took place after early humans started making tools" (Morton Hunt. The Universe Within: A New Science Explores the Human Mind. New York: Simon & Schuster. 1982. 45.)

'Hominids': Homo habilis... homo erectus... homo sapiens... homo sapiens sapiens  The first human being - 'homo habilis'- appeared rather abruptly with 750cc of brain about two million years ago. 'Homo erectus' appeared with 900cc to 1300cc of brain about half a million years ago - 500,000 years ago. Then there was rapid brain development which culminated in the evolution of the true human brain of 'homo sapiens'. An early form of homo sapiens appeared, with a 1400cc brain about two hundred and fifty thousand years ago. And the modern human being - homo sapiens sapiens - appeared with 1500cc brain about forty thousand years ago.

 As a product of human evolution through natural selection, the thinking skills of the brain can best be understood in terms of behavioral adaptation and survival. The survival of the individual depends on meaningful learning and adaptive behavior.

As the result of evolution networks of neurons 'neuronal networks' and ‘streams’ of chemical 'transmitters' - 'transmitter channels' are linked with positive and negative control loops influenced by environment and nurture... constitute the biological basis of intrinsic motives for human behaviour or 'human needs'.

Survival value of the brain as 'meaning maker' In the evolution of the human species, survival of the human organism depends on the natural selection of brain functions which enable the individual to derive meaning from environnmental stimuli. Brain functions which produce effective thinking produce constructive or 'adaptive' behaviour which adaptive and increases the chances of survival. Brain functions which produce non-effective thinking produce destructive behaviour which is non-adaptive and decreases the chances of survival. The human species has evolved a brain with the specialized capacity for meaningful learning and adaptive behavior. This is in contrast to the evolution of other organisms whose survival and adaptation have depended on the development and specialization of various other organs and other forms of instinctive behaviour. In the evolution of the human organism survival depends on the skills of learning. Human survival depends on the human instinct for learning and the ability to learn for intelligent behavior. The natural selection of intelligent behaviour has produced the human brain as the biological organ specialized for the functions of speech and learning. They are as natural to the brain as breathing is to the lungs. The complex totality of the learning skills is a product of the evolutionary process.

 Survival value of specialised brain functions  The natural process of learning is a function of the brain as the maker of meaning... organ of 'learning'... 'meaning-maker' or 'brain'. The functions of the human brain are the product of millions of years of evolutionary process through natural selection.

 Survival of the human species depends on development of specialized brain functions.

 The 'emergent properties' of brain functioning lead to those aspects of human nature which have survival value for the human organism as a social organism and the human species as a social species.... 'social values' ...'spiritual values'... values which depend on development of consciousness... 'moral consciousness' or 'conscience'.

As a product of evolution through natural selection,  the human brain is best understood as an organ of learning adapted for the survival of the species. The mental functions of learning and memory are natural outcome of human evolution, survival of the human species depends on behavioural adaptation or 'adaptability'. Human adaptive behaviour depends on brain development and the development of the thinking skills.

Implications for education

In the evolution of all living organisms, survival depends on the genetic transmission of instinctive survival skills.

The functions of the human brain are the natural outcome of millions of years of evolutionary process through natural selection.

Evolution of the human brain.. brain’s self-organisation has been naturally selective of ways of life which guarantee survival of the human organism as a social organim.

'holistic education'

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(reference:Restak The Brain)