It is the result of 500 millions years of evolution, constantly changing, and yet still evolving today.
It controls every part of our body, every aspect of our life and every step of our behavior. It creates feelings such as joy, love, anger or sadness. It makes us conscious, gives us our mind, human being instead of beasts. Without it, we wouldn’t have innovation and creation processes, those that shape our modern society and give us the ability to rule the world, and soon beyond.
Every time we pronounce the word brain, the first thought is a picture of a big pink sponge with a lot of circumvolutions. Indeed this is our brain, but when you dig into it, it is a far more complex system, a puzzle made of different parts. How such engineered piece came to existence? What is it made of? What does the word “Brain” really include?
Models exist to explain the evolution of the brain and one of these is the MacLean triune brain model. It states that there are three distinct parts in our brain, the Reptilian brain, the Limbic brain and the Neocortex (or Isocortex), and these parts were created one after the other. These brain systems are seen in mammals, animal and living things. Each of them is a result of our evolution since our oldest ancestor, and have different functions. According to the theory, the development of the brain happened in three steps: first the reptilian brain was created, than the limbic brain appeared and finally the Neocortex.
Even if this model is correct from a biological point of view (there are indeed three different parts in the brain), it has been challenged and refuted. The evolution of our brain hasn’t been made through different steps that added up to each other, starting with the reptilian brain. Researchers have discovered that reptiles also have a Neocortex. Therefore our common ancestor probably had one too, or maybe just a simpler brain structure. This discovery contradicts MacLean model of a different steps brain development during evolution.
Now let’s dig into each part. Their functions cover every aspect of our life, from the simplest requirement (life functions), adding on emotions and feelings to end up with complex processes such as consciousness.
The Reptilian brain
It is composed of the Cerebellum and the Brainstem. It is the oldest brain system created and mostly ensures physical life functions: breathing, cardiac rhythm, temperature management or even balance. Without it, we would not be able to live or walk, from a physical and biological point of view.
The Limbic brain
Mostly made of the Hippocampus and the Hypothalamus, the Limbic brain has a vital role in our attitudes, behaviours and acts. Memorizing likeable and non-likeable behaviours or actions is crucial in building relationships. The limbic brain gives the ability to memorize things, events, person and faces. Therefore it plays a huge role in socialization. Finally it is responsible for our emotions and feelings. Our emotional brain is in fact mostly our limbic brain, the feeling of love is created in this system, but being able to use words to describe it is the role of the next system.
It makes up the biggest part of our brain. Occupying more than 50% of it, the Neocortex is the key of human thought. Since the first mammals, the Neocortex has had a non-stop growth, becoming much bigger than every older structure. On this part of our brain lies human consciousness, the human ability to communicate (formulation and understanding language), its creativity and imagination, its capacity to think, analyze and decide. These abilities come from the two hemispheres, both located in the prefrontal cortex; human have these two hemispheres extremely voluminous compared to other parts of the brain. The Neocortex is very soft, and possesses in theory almost unlimited learning capacity.
Fun fact, the volume development of the Neocortex during evolution happened literally faster than the skull, being pleated and packed is the result. In fact, these circumvolutions are an evolution response to allow a bigger cortical surface in the skull. Also, they generate a much better efficiency in complex thoughts.
One could ask why do we have such disproportionate Neocortex, especially compared to other parts of our brain? The answer lies in its utility, as always when it comes to evolution. First observations of a bigger Neocortex come from predator mammals. Hunting based life requires a much efficient sensorial and motor system, having a bigger Neocortex allows efficient movement control and senses utilization. These functions are located in this area and give an advantage to predator species. Moreover, meat brings much higher nutritive food, allowing a bigger neuronal volume to be fed.
Beside predator requirements, the Neocortex is involved in socialization, prediction of behaviours, group life and increasing complexity in social environment. While the limbic brain is involved in behaviour creation, the Neocortex really kicks in to create thoughts and relationships. It is a big advantage for species; for example cortical areas responsible for language have been kept due to the changing environment and the ability to improve such behaviours.
Our brain and our skull haven’t always been so big and so efficient. Our ancestor had smaller skulls and through evolution, it has increased in size. As we can see on the picture below, the brain volume has more than tripled since our oldest ancestor, the Australopithecus. And if we keep on this track, we can also see that the Neanderthal man had a bigger skull than us! However, his cognitive capacities were never as good and as developed as us, proving indubitably that skull/brain size and intelligence are not related.
As the human body was evolving through the ages, so did our brain. It is the result of a long work, every time adding on new features like a puzzle: change the environment, change the requirements and new areas will be kept to create the best response to these changes. From the dark ages of humanity to modern societies, our brain led us and will keep on to the next steps of human kind. It is fascinating to know that every person has inside him or her the most engineered system of all times, and that this system built itself. As our environment changes, so does our brain. New abilities were developed in response to old requirements (such as sense, intuition, consciousness and feelings developed to protect ourselves) and this capacity can only make us wonder about the newt abilities that have yet to be developed.