As scientists and archeologists have discovered, prehistoric humans have evolved into stronger, more advanced versions of the genus Homo in which we see today. One of the most distinct adaptations of the human is the enlargement of the brain, as well as advancements in specific areas of the brain, which have lead to increased intelligence and function. The growth of the mammalian brain began in three sections of the “Triune Brain” theory proposed by Paul Maclean; the reptilian brain, limbic brain, and eventually the expansion of the cerebral cortex in humans. Modern human’s brain retained the primitive reptilian and limbic brain because of their role in basic bodily functions such as homeostasis and human emotions, therefore evolution lead to expansion of these parts rather than deletion. Around 145 million years ago came the development of the prefrontal cortex, which introduced the ability to speak, conceptual thought, imagination, and a sense of consciousness, specifically in humans. These behavioral complexities allowed for humans to become more aware and connected with other humans as well as their surroundings, enabling more success in finding food, detecting danger, and adapting to environmental changes. The development of the prefrontal cortex introduced the greatest mass and enlargement of the human brain with the two hemispheres of folded and layered neuron tissue. Studying the brain of our ancestors is close to impossible due to decay of the soft tissue, therefore data is observed and collected from skulls of prehistoric hominids along with comparing the brain structures and functions of modern day humans and related primates. Such comparisons of the brain, especially the prefrontal cortex, are seen between chimpanzees, gorillas, orangutans, gibbons, and macaques with humans obtaining the largest brain. The evolutionary advantage that separate humans from their hominid relatives came with the development and increased complexity of the prefrontal cortex and its subparts; these advancements and functions were a huge evolutionary advantage which allowed for humans to be a powerful, well adapted species suited for a more modern critical thinking environment.
The various parts of the prefrontal cortex and their functions evolved over time and allowed for humans to adapt and excel in their current environment. The evolution of the brain followed successions and additions in different species; starting with the most primitive animals such as reptiles, then more and more advanced organisms such as primates. The prefrontal cortex consists of four lobes that evolved over time, which all coexisted and coevolved to adapt to the changing environment by adding on additions to the current parts. The largest of the lobes is the Frontal Lobes, which was once responsible for voluntary movement and then became more complex with the additional functions of reasoning, planning, emotions, and converting thoughts into words (The Brain). Next are the Parietal Lobes which control senses such as taste, touch, temperature, and pain, thus connected to the Peripheral Nervous System to receive information about the surrounding environment (The Brain). The Occipital Lobes collect visual information and depict it into shapes, colors, and movement in the Visual Cortex, also remembering the images for later recognition (The Brain). The last of the main lobes are the Temporal Lobes; these along with the Occipital Lobes are connected to the Peripheral Nervous System and also collects verbal and visual memory while also distinguishing the volume and frequency of sounds (The Brain). All of these parts together function simultaneously with other complex sections of the brain, all connecting and advancing with stimulation and adaptations to the primates and eventually human’s environment.
The size and compacting of the prefrontal cortex and its lobes formed a faster, more efficient brain that allowed humans to better adapt while conserving energy. From Australopithecus to modern day Homo sapiens, height and body mass has increased as the species became more proficient in their diet and protection from dangerous or harmful pressures. The brain mass increased as a direct correlation to increasing body size to keep up with the greater demand for bodily controls and functions. The mass of the prefrontal cortex in humans makes up 80% of overall brain mass, enabling increased neuron connectivity, sensory reception, and predictive power (Hofman). This increase also included more “white matter” tissue which makes up the lobes and neuron connections; to remain energy efficient and require less skull volume, the brain increases its folds as the mass increases to form a more compact brain (Hofman). Scientists believe the increase in body mass and brain size are both related to the “expensive tissue” hypothesis, which states that due to the high energy demand of the brain it is considered very valuable, or “expensive” (Park). The organ with the closest energy demand to the brain is the intestinal tract, which began to shrink as humans evolved a more nutrient-rich diet as they learned to hunt and cook with fire, thus freeing up space and resources for the brain to expand (Park). Along with a more nutritious diet, scientists believe that simple tool making played a major role in increasing cognitive functions of the brain by devising an easier way to hunt for meat, technical skills with stones to “knap” a knife or finding wood for a fire, and increasing social skills when hunting in packs and sharing food with others (Bril). Although the increase in brain size is only evident over generations, these theories and observations help to uncover reasons for the expansion and gives greater insight to ancient humans who left little evidence behind.
Although tangible evidence of ancient human brains is impossible to study, scientists run experiments on related primates and study the remains of early hominids to collect data and understand the human brain before modern day man. Studies were done on the skull size and relative age of Australopithecus, ancient Homo sapiens, and Neanderthals, with results showing that these hominid species brain sizes peaked at a later age than other primates, increasing cognitive development and physical maturity faster than other mammals (Seymour). This increased ability to process and obtain crucial information at a younger age meant that humans had a higher survival rate as juveniles, being more aware and interactive with their environment for food and protection. These studies of ancient hominids were done using endocasts, or molds of the inside of the skull, and creates a useful depiction of the brain size and the patterns of the folds (Jerison). Along with skull sizes, scientists observed the increase in the Carotid Foramina between Australopithecus, ancient Homo sapiens, and Neanderthals; this allows the internal carotid arteries to reach the brain tissue and supply blood and oxygen (Seymour). The increase in blood flow to the brain is directly correlated to higher metabolic rates within the brain, allowing for faster processing of information, greater memory capacity, and increased neuron connectivity, thus leading to a more specialized and cognitive brain (Seymour). With limited resources, scientists uncovered evidence of increasing brain size and complexity of the hominid brain which is seen today in modern day humans.
The growth of the prefrontal cortex in the human brain better adapted the species to the ever changing environment and allowed for survival and success. As the human species were forced against environmental pressures such as finding food, staying warm, finding protection, and staying alive in the volatile African forest. Once humans became bipedal and evolved from climbing in trees to venturing the savannah grasslands, they were faced with new tasks in a whole new environment; hunting for food, building protection, and mating all offered new resources and required advanced cognitive interactions that lead to language, social structure, and eventually societies (Park). Humans also grew and adapted by responding to positive feedback when they study the surroundings for possible food or keeping dry during the cold, with these decisions keeping them healthy and alive (Park). Natural selection played a large role in how the brain evolved due to the pressures applied, and the most successful to move on were excelled at problem solving and forming sufficient relationships for food, respect, and reproduction (The Brain). According to the “Machiavellian intelligence” hypothesis, the more social individuals acquire more resources and relationships that benefit them physically and reproductively, and their genes will be further passed along (Park). Mutations and adaptations that are passed down generations creates an ever-evolving gene pool in which the hominid brain became the well adapted, cognitive organ that we see today.
The stimuli and pressures of the ever changing environment create opportunities for adaptation or destruction within a species. Such species that show the greatest advancements in are the Homo sapiens, who are theorized to originate from primates and evolved into the intellectual beings of modern day. The driving force of the Homo species’s success was the expansion of the brain, specifically the prefrontal cortex. This section of the cerebral cortex contains four main lobes; the Frontal lobes for reasoning and emotions, the Parietal lobes for senses of touch and taste, the Occipital lobes for visual perception, and the Temporal lobes for visual and verbal memory. The volume increase of the brain was largely due to an enhanced diet, tool building, and social skills that required greater cognitive function and innovative psychic to handle the challenges at hand. The theories formulated around the prefrontal cortex emerge from the experiments on primate relatives along with observation of the ancient remains through modern technology. The results indicate increased size from skull remains and higher metabolic rate from greater blood flow, thus creating stronger neuron connections and greater tissue mass which allowed for faster responses to the environment and its pressures. The human brain had many elements that affected its evolution; the changes were seen in the species as they became bipedal, made tools, and cooked their food, surviving the elements of the environment and becoming aware, and interacting with animals and each other to form relationships and social skills eventually leading to societies. Along with adaptations came the effects of natural selection, as the most successful surviving and carrying on their genetic information to the next generation. Mutations within the newest generations created diversity within the species and offered new functions and adaptations to be added and evolved. The humans of today are a result of millions and millions of years of minute tweaks and changes that lead to the most complex and prosperous species known to date.