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Like everything else in nature, the human brain can only be truly understood by tracing its evolutionary pattern. It is a structure that has adapted over time to perform a variety of vital functions, while at the same time being compelled to survive by selectively ridding itself of its more gratuitous functions. These selection procedures, in turn, enhanced the functional capabilities of the nervous system in accordance with the changing needs of mankind.
Billions of years ago, life existed only in the form of single celled organisms. These organisms were sustained through their own chemical processes until they gradually evolved into the multi-celled beings that first appeared approximately 680 million years ago. More complex animals, including man, subsequently evolved from these multi-celled beings.
The evolution of the human brain followed a similar course; moving from the simple to the complex over an extended period of time. The billions of cells that work together to make the brain and body function harmoniously have numerous critical functions. The brain is after all a far more multi-functional organ by nature than other, less complex organs such as the heart or the liver. Yet akin to the rest of the human body, the brain has adhered to Charles Darwin's “natural selection” methodology by ridding itself of less important functions while enhancing the more essential ones over time.
It is a fact that as man evolved, certain mutations took place within the nervous system that forced it to evolve in time with the body. Just as external physical changes were selected as either worthy or unworthy by the environment, mutations in the nervous system were also forced to prove their might against environmental challenges.
For example, man's ancient ancestors acquired “new and improved” sensors as a necessary means of survival, which naturally forced the neural control of those sensory enhancements to occur simultaneously. Consequently, as man's ability to survive began to necessitate increasingly complex actions and reactions to his environment, the nervous system was also compelled to adapt accordingly.
As recently as two centuries ago, the function of the human brain was still a complete mystery. It wasn't until the influx of technological advancement that a true understanding of the human brain began to emerge. By studying fossils, scientists learned to differentiate between ape-like and human-like cranial structures.
Through dissection, we have been able to identify all elements of the brain's complex structure. By observing brain function through such techniques as Magnetic Resonance Imaging (MRI), the active portion of the brain can be studied while the subject is performing certain functions. For example, if the subject moves his right foot, a section of the parietal area of the left hemisphere will demonstrate that activity is indeed taking place. Modern technology such as brain mapping also allows us to make correlations between regional damage and resulting neural performance, such as in instances of brain damage.
Relative to body mass, brain volume tends to increase gradually over time; a process from which humans have benefited more significantly than any other beings. Humans do have the largest brain size in proportion to the body when compared to all other mammals. Ostensibly, larger brain size is akin to more complex behavior and greater intelligence. However whether the larger size of the human brain emerged in preparation for our complex behavior and culture, or as a consequence of it, remains to be seen. There is no disputing that larger animals have larger brains than smaller animals of comparable construct and functionality. This is primarily because additional neurons are needed in order to increase the body tissue necessary to employ and sustain them; which means the largest animals must have the largest brains.
However, if brain function is reliant merely on the ratio of neurons to body cells and the variations between cell size and species are immaterial, then brain weight would be expected to be consistent with body weight. Yet in truth, for many neural functions, body size is irrelevant. For instance, sensory receptors that monitor an individual's blood pressure or temperature would not need to expand with body size. Therefore the real connection between brain to body mass is often found to exist in independent physiological systems.
One of the reasons that the evolutionary process of the brain is so important is that it elucidates many age-old mysteries surrounding human behavior and emotion. In The Emotional Brain, Joseph LeDoux examines the roots of human emotions and clarifies the notion that many of these emotions also exist as part of complex neural systems that evolved to facilitate the ultimate survival of mankind. According to LeDoux, emotions, unlike conscious feelings, originate in a deep level of the human brain. Therefore conscious feelings are essentially immaterial when determining the manner in which the emotional brain functions.
LeDoux additionally contends that our emotional responses are permanently wired into the brain's complex circuitry, yet the components of our emotional repertoire are learned through experience. A host of common psychological disorder such as phobias or posttraumatic stress are simply malfunctions in the manner in which our emotional circuitry processes information. For this reason, a deeper understanding of how these mechanisms normally function could have a substantial impact on how we view human emotion, as well as how we treat emotional disorders.
One of the most adamant claims LeDoux makes is that our emotional systems evolved as a means of coordinating physical reactions with external demands. He is convinced therefore, that emotion could not possibly exist “without a body attached to the brain that is trying to have the feeling”. His perspective on the closely related argument that the body would not provide enough variety of signals to represent the different emotions we experience is also of concern to LeDoux in that he unwaveringly supports the notion that body signals can easily provide the diversity of emotional patterns needed to express them.
The nervous system, with its sensory organs being at first genetically determined, constitutes the first set of biological filters that distinguishes external reality from our internal representation of that same reality. Furthermore, our genetically endowed biological limitations allow us to understand only a small portion of the true nature of human functionality. This is in part because our emotional development is so evenly correlated to our physical development. This correlation exists not only in a physiological capacity, but also in a psychological one. For example, from the moment an individual identifies with his body, and becomes aware of his surrounding environment, the rising level of emotional cognizance creates an existential need to survive, along with a powerful fear of death. This is the level in which man's emotional and thought processes, as well as his personal will, first begin to develop. For instance, the period in which an infant begins to develop the capacity to differentiate between himself and his surroundings is most often the same period in which the child's motor skills begin to develop. The child starts to walk and to talk and at the same time, and becomes more emotionally separated from others due to an increased sense of awareness and independence.
The human nervous system is a complex mechanism maintained by numerous diverse yet mutually supportive functions. In fact, the modern human nervous system is comprised of approximately 100 billion neural functioning cells, supported by what has been estimated to be almost ten times that amount. This essentially means that the diverse amounts of interconnections that occur within the human brain are virtually immeasurable. Therefore limitless applications also exist for studying human brain function as it has evolved over time.
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