Evolution of the human brain
When this impossible struggle for existence continued, the environment was not always favourable to this struggle. When the environmental conditions changed, many organisms died but a few were able to survive by adapting to the environmental conditions. Because the adaptation was some kind of change in the organism, the organisms began to change in structure and function in adapting to environmental conditions. This changing evolutionary process therefore began to develop organisms with differences in structure and function. As a result of this adaptation many different species of organisms evolved, with a variety of structures and functions befitting a variety of environmental conditions. They also began to develop what are called systems, where several organs combined to deal with a problem in the environment. As conditions in the environment became more and more challenging, the systems became correspondingly more and more complex. As systems became complex, they began to develop cardiovascular systems that circulated blood, and even nervous systems that carried messages like telephone wires. As the nervous systems began to develop more complex structures and functions, it lead to the development of a brain. The brain began to develop from a primitive structure called the brain stem which regulates basic life functions such as respiration, digestion, blood circulation, and metabolism – these are the autonomous functions that kept the organism alive and healthy.
As conditions in the environment became more and more challenging, the brain gradually began to evolve further and so aid the survival of the species. This resulted in the development of another part of the brain called the limbic system that helped in starting an emotional reaction in response to stimulation by the environment. It is this reaction that we now call emotional arousal. The Limbic System is the emotional command center of the organism, which is responsible for regulating differences in the mood or temper such as calmness and excitement. Within the Limbic System is a structure known as the Amygdala which is responsible for scanning the environment through the sense organs, to detect signs of potential threats and danger to the organism. When aroused, the Amygdala triggers the fight or flight response, to protect the organism from harm. It is this reaction that is commonly called stress today, which if prolonged can develop into the general adaptation syndrome, which turns stress into distress.
As the brain evolved further, higher forms of organisms such as mammals evolved, with the formation of the Cerebrum which contained the Cerebral Cortex, or Neo-cortex that is responsible for thinking. As evolution progressed further the Cerebrum developed into two hemispheres: left and right. Within these two hemispheres of the Cerebral Cortex came four major pairs of lobes: frontal lobes, temporal lobes, occipital lobes, and parietal lobes. In this way the human brain developed with a Pre-Frontal Cortex (PFC) in the frontal lobes, which equipped the human being with highly advanced and sophisticated cognitive functions such as planning, goal setting, decision making, judgment, reasoning, rationalization and speech.