The Evolution of the Human Brain

The human brain is a feat of evolution: it has allowed humans to have complex thoughts, conscience, build tools, create fires, and much more.

Humans did not acquire this simply by chance. Evolution throughout our ancestral past has shaped and moulded the human mind to its state. The earliest of ancestors, including apes, had very small brains, but as evolution progressed, so too did the human brain. The rapid progression of human intelligence has been attributed to environmental changes causing humans to change with their surroundings for survival.This lead to the expansion of specific areas of the brain, vastly differing maturation of humans compared to our ancestors, changing genetics, which is just some of the changes that has occurred in humans.

In this present paper, the changes and reasons as to the changes of brain over the course of human evolution are investigated. Research into this topic shows studies similar correlations with respect to one another, with the majority of sharing and overlapping in many opinions on this topic.Majority of research discussed has fairly been recently conducted within the last decade, and virtually all were conducted by western or European researchers. The most discernible change in the human brain is its absolute size.

The average brain of the modern human is up to four times larger than of our earliest ancestors. Currently, the average fully grown adult Homo sapiens is approximately 1200 to 1600 cubic centimetres and weighing three pounds. In comparison, the earliest trace of human ancestors, the Australopithecus clan had brains slightly greater than apes, around 400 cubic centimetres.Anatomically the Australopithecus were bipedal akin to humans, but intellectually akin to primates, which suggests that bipedalism preceded the growth of the brain on the timeline of human evolution. The next ancestors, Homo habilis had an increased cranial capacity of approximately 650 cubic centimetres. With this came the earliest evidence of tool-making by a species which has been attributed to increased brain capacity.

Homo erectus had a cranial capacity of approximately 850 to 900 cubic centimetres.This increase has been associated with the exodus of the Homo genus from Africa into other continents as they move to track the sources of food caused by the change in climate. The greatest evolutionary bound in brain capacity was that of Homo neanderthalensis with a capacity of approximately 1300 cubic centimetres, which in some cases is greater than that of the average modern Homo sapiens. This may have been a result of Homo neanderthalensis having larger bodies that tend to need increased neurologic control mechanisms. (Hurlbert & Loreto, 2011; McKie, 2000; Davis, n. d.

Homo sapiens, when compared to all other mammals, have the largest brains with respect to their body size. This is measured by the encephalizaton quotient or EQ, which is the extent that the brain size of a species deviates of the “standard” species. For mammals, the standard is a cat, with an EQ equivalent to one, or the “control” standard. The human is seven to eight times larger than expected with primates with the nearest mammal on the list being half of that. (Roth & Dicke, 2005) Increased brain size does not generally equate to greater intelligence; humans do not have the largest brains of all animals.When looking at the brain size, it is also important to look at which parts and sections of the brain that has been expanding.

Over the course of human evolution the absolute size of the visual cortex compared to apes, has seen little difference, but the human nonvisual neocortex & prefrontal cortex is larger than that of primates and human ancestors, which allowed for social competencies unique to humans, such as theory of mind, language, and the ability to mentally simulate social situations. Dunbar, 2007) The prefrontal cortex is the section of brain responsible for executive functions such as decision-making, problem-solving, and simulate of situations. The neocortex is associated as being the area of the brain responsible for complex cognitive processes affiliated with reasoning and consciousness. (Dunbar, 2007; Flinn, Geary, & Ward, 2005)Although a larger brain in theory may on the surface appear to have its benefits, it comes with many challenges. The adult human brain weighs about two percent of total body weight, but consuming over twenty percent of the body’s energy.

Dunbar, 2007; McKie, 2000) This has led to significant changes in the dietary needs of humans, such as the introduction of meats, fats and proteins to the diet. Unlike apes, hominid mothers needed to eat more foods that provided higher concentrations of dietary fats, such as bone marrow and animal brains. This allowed the mothers to provide fatter and more nutrient-rich milk to their infants, essential to brain growth. (Sloan & Garrett, 2004) Thus, improved quality of diet is selected by improved motor cognition skills, better recognition of higher quality foods, and improved tactics of acquiring them. Roth & Dicke, 2005)This larger brain is also the foremost reason as to the extended childhood of Homo sapiens in comparison to primates and human ancestors.

Extended childhood in humans was fundamental for brain development since fetal brain development was restricted due to bipedalism causing smaller birth-canals. Furthermore, the longer duration for brain development provided time for complex development and experience to acquire essential social skills. (Flinn et al. , 2005) Another pitfall to the evolution of the human brain is that it is in some ways more genetically fragile with respect to human intellectual and emotional abilities.

Almost ten percent of all human genes have implication in intellect function, and just a single mutation can result in a disability. Based on estimates, the occurrence of harmful mutations in the gene structure of a human is highly likely within 3000 years of modern man, and individuals may sustain two or more deleterious mutations to the intellect or emotional functions. (Crabtree, 2012) Despite the evolutionary many benefits and gradient expenses with human intelligence, increased brain size did not occur because it was able to expand by itself. Environmental factors are what led to the evolutionary changes.A fundamental principle of evolutionary theory is that evolution is the balanced outcome between costs and benefits. Since the price of maintaining a large brain is greater, it is inherently improbably that expansion of the brain will evolve without a selection factor being adequate to overcome the high expenses.

(Dunbar, 2007) There has been a strong correlation between increased temperatures in the global climate and increased endocranial volume. Over the past three million years, the average global temperature has been steadily increasing, as well as the braincase of human ancestors.Strong evidence of this is seen between the period approximately 200,000 to 800,000 years ago where the Earth’s climate experienced the greatest temperature fluctuations which correlated with the greatest increase in brain development among human ancestors. (Hurlbert & Loreto, 2011) It is believed that for the duration of evolution, hominins augmented their abilities to contend with multiple environments rather than specializing on a specific environment. One of these specializations was a larger brain that was capable of producing novel solutions to a variety of unique and diverse survival challenges. The Smithsonian Institute, 2011) Intellectual capacity has not increased significantly in humans in the last 50,000 years which coincides with the final wave of the exodus of Homo sapiens out of Africa.

(Crabtree, 2012) The emergence and evolution of hominins is both a combination of social competition and cooperation was the result of increased ecological dominance, which is predominance of a species in the ecosystems. (Dunbar, 2007) As a result, this caused humans to be more socially and psychologically different from each other.This concept is what was believed to have created individualism and personality unique to humans. The intricate social cognitive and linguistic capacities were favoured as it provided the ability individuals to conjecture and influence social interactions.

Unlike, the static ecological challenges, the social surroundings were a catalyst in increasing the significance of social competences and auxiliary brain systems. (Flinn et al. , 2005) In conclusion, the research of this topic reveals that the expansion of the brain is a result of environmental factors that led to the selection of specific biological traits.These traits were increased brain capacity, and a greater prefrontal and neocortex. These evolutionary leaps in intellect came with disadvantages, requiring one fifth of the body’s energy, and a longer time to reach sexual maturity. The human brain has significantly changed over the course of evolution.

This compilation of all the sources shows very similar findings in terms of what has occurs in the past, but the majority fail to discuss the implications this will have on the future of humanity.The research does not go into detail or even discuss the impacts that evolution of the human brain will result to in the future. It is recommended that further research be done into the implications evolution of the brain and intelligence will have on humans. Also, study should be done as to how the human mind changed over the course of modern man, within the last 50,000 years, which will allow for better understanding of how humans are currently evolution.