Human organs, much like the human heart, have changed and evolved over the history of time. The human brain is no exception to this natural phenomena. Based on Charles Darwin's idea of Natural Selection, species that had larger brains capable of complex functioning seemed to be a favorable adaptation. The ability to take in and understand new situations proved invaluable to the survival of Homo sapiens. Some scientists believe that as the environment on Earth evolved, humans did as well. The ability to survive these environmental changes was directly due to the size and function of the brain to process the information and act upon it.
Early Human Ancestors
During the reign of the Ardipithecus Group of human ancestors, brains were very similar in size and function to those of a chimpanzee. Since the human ancestors of that time (about 6 million to 2 million years ago) were more ape-like than human, the brains needed to still function like that of a primate. Even though these ancestors tended to walk upright for at least part of the time, they did still climb and live in the trees, which requires a different set of skills and adaptations than that of modern humans.
The smaller size of the brain at this stage in human evolution was adequate for survival. Toward the end of this time period, the human ancestors began figuring out how to make very primitive tools. This allowed them to begin hunting larger animals and increase their protein intake. This crucial step was necessary for brain evolution since the modern human brain requires a constant source of energy to keep functioning at the rate it does.
2 million to 800,000 Years Ago
Species of this time period began moving to different places across the Earth. As they moved, they encountered new environments and climates. In order to process and adapt to these climates, their brains began to get bigger and perform more complex tasks. Now that the first of the human ancestors had begun to spread out, there was more food and room for each species. This led to an increase in both body size and brain size of the individuals.
Human ancestors of this time period, like the Australopithecus Group and the Paranthropus Group, became even more proficient in tool making and got a command of fire to help keep warm and cook food. An increase in brain size and function required a more diverse diet for these species and with these advances, it was possible.
800,000 to 200,000 Years Ago
Over these years in the history of the Earth, there was a large climatic shift. This caused the human brain to evolve at a relatively rapid pace. Species that could not adapt to the shifting temperatures and environments quickly went extinct. Eventually, only Homo sapiens from the Homo Group remained.
The size and complexity of the human brain allowed individuals to develop more than just primitive communication systems. This allowed them to work together to adapt and stay alive. Species whose brains were not large or complex enough went extinct.
The different parts of the brain, since it was now large enough to not only accommodate instincts necessary for survival but also more complex thoughts and feelings, were able to differentiate and specialize in various tasks. Parts of the brain were designated for feelings and emotion while others stayed with the task of survival and autonomous life functions. The differentiation of the parts of the brain allowed humans to create and understand languages to communicate more effectively with others.