THE HUMAN BRAIN AND EVOLUTION

Researched by Academy House Team
Edited by Mousab Kassem Azzawi, MSc, MD, PhD.

Each human being has two nervous systems in his body, the central nervous system, which is composed of the brain and spinal cord, and the peripheral nervous system, which is composed of everything else.

There has been a perpetual conundrum surrounding the primacy of nature (in terms of our genes) versus nurture (exemplified in culture and education) in explaining how our brains work, and consequently, how our mind and perception are formulated. In fact, it is commonly agreed now that both elements play an essential role in creating an efficient and -function-al brain.

The hallmark of our brain is that it can perform a period of sophisticated processes and actions that other animals cannot perform to the level of perfectionism we can achieve as humans.

Charles Darwin, the father of the human evolution theory, suggested that our survival as a species depended on the fact that humans are more intelligent than the other species that made us more capable of adaptation to the conditions of our environments, which eventually led for the humans to be the dominant animals of our planet.

The social brain hypothesis argues that larger social groups led to the development of our brains in terms of size as well as connectivity and -function-ality. The theory suggests that sustaining complex social interactions, including understanding the intentions and motivations of the other members in our social group, turns out to take a lot of supporting neural substrate and optimisation in terms of increased brain size and efficiency.

Many scientists believe that humans conquered the world because they first conquered their isolation. Those with the talent to create allies within a larger social group effectively increased their biomass without actually increasing their biomass by taking the power of social cooperation and collective efforts coordination to an unprecedented level. In other words, the social brain hypothesis argues that the essence of our successful evolutionary history and survival stemmed from our ability to make, and keep, friends within our social group.

The flip side of the social brain hypothesis is called the variability selection theory, which tries to explain how our interaction with the conditions of our physical environment led to creating smarter human beings. It is widely believed that our ancient relatives came from Africa where we diverged from what would become chimpanzees about 6 to 8 million years ago. During those 8 million years the climate was swinging dramatically among several extremes, ranging between ice ages and wetter warmer climates every 100 years´-or-so. Around 250,000 years ago, our species, Homo sapiens (the wise man!) came into being. Variability selection theory suggests that climate change has been a vital player in our evolutionary history for a long time. It argues that the pressure of climate change necessitated that humans should get more intelligence if they did not want to become extinct like other species who were unable to adapt to such change in the environment, such as the dinosaurs.

In addition to the social brain hypothesis which tries to explain how we got bigger human brains, and the variability selection theory which defines the human intelligence as an adaptation to the ever-changing climate over the history of human evolution-;- natural selection may be the third pillar that explains the evolution of our brains. Evolution through natural selection is a deterministic process favouring the mechanistic selection of successful genetic traits that facilitate better adaptation to the environment by a human being happened to have these genetic traits within the genetic codes of his chromosomes.

During fertilisation, the genetic codes of the parents get mixed together like being put in a blender. One result of this mixing process is generating what is called “a mutation”, which is a new genetic code different from the ones inherited from the mother´-or-the father. Most of the mutations are harmless and the vast majority of them do nothing to increase´-or-decrease the humans ability to survive his environment. However, not all mutations are neutral. Sometimes, humans get harmful mutations which are responsible for the majority of miscarriages. In other instances, a few of these mutations may be beneficial to the organism by creating new traits that make the adaptation to the environment more manageable, and increases the chances of survival and reproduction, which eventually increases the concentration of these beneficial mutations in the overall genetic pool of the social group. For example, recent genetic studies of fossil samples affirmed our assumptions that the original inhabitants of the Western and Northern parts of our planet were dark-skinned people when humans emerged from the last ice age 6000 to 10,000 years ago, which is not consistent with the variations of skin colour we can observe among the current populations of our planet. The answer to this paradox is “natural selection” in which the mutations that resulted in fairer skin colour traits, which made it easier to absorb the vitamin D from the sun and eventually increased the survival rate and the reproduction chance of the people who happened to have these mutations, resulted in the variations in skin colour we currently have in the world, which is a mere adaptation to the environment and has nothing to do with anything else other than sunlight, vitamin D and our critical need for these elements to survive physiologically.

It is worth noting that the environment did not push anybody to do anything. That environment changed and changes only according to its laws. Besides, we did not deliberately decide to evolve distinctive human characteristics so that we could survive. We do not have the power to control our genetic mutations either by kind´-or-rate. Genetic mutations happen randomly similar to what happens when we roll the dice. Those who were lucky from our ancestors won some favourable genetic mutations and traits that were suited to a particle environment. This mere luck facilitated their survival and reproduction.

In the domain of our brains’ anatomy and physiology, the same rules of natural selection apply. Those with traits that created more social and intelligent brains survived better the harsh conditions of the environment and could reproduce more to bring our generation into being.

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