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Brain Evolution

The brain, the masterpiece of creation, is almost unknown to us.” -Nicolaus Steno 1669

What is the purpose of the brain?

This is a question that has long plagued neuroscientists, biologists, and philosophers alike. If you google this question you will find the textbook cut and dry answer, which is the ‘brain serves as the center of the nervous system and coordinates all body function’. This is true; however, how then, can we account for the organisms that do not have a brain? And what is it about the human brain that differentiates us from other animals?

To start, I would like to use the example of a sea squirt. Sea squirts are fascinating creatures. Most people think of sea squirts as immobile creatures that live on rocks. However, they do not start off immobile. When a sea squirt first develops it has a primitive brain and full spinal cord and can swim until it finds a hard place to latch onto. Once it attaches to a surface it no longer has a need to move and effectively eats its own brain!

When we consider this example and look at creatures that have a more advanced nervous system with a brain, one thing that they all have in common is the ability to move. As we go up the evolutionary chain we see an increase in more complex movements: slithering to quadrupeds to bipedalism. With the increase in movement complexity so too comes the growth and sophistication of our nervous system and brain.

As humans, we have one of the most highly developed brains. When we are first born, we are governed by the primitive center of our brain, called the brainstem. Our cerebral cortex (the wrinkly part we think of when we think of a brain) is only approximately 25% developed. As we begin to take in our environment through our senses our cortex begins to grow and mature. One of the major sensory inputs that drives brain growth and development is movement. In essence, information coming from our body triggers brain growth in a bottom up fashion. Then, as our brain begins to mature, it starts to exert more control over our body from the top down.

Much of this brain growth happens within the first six years of life. During this time the human cerebral cortex begins to develop specific functions that allow us to plan, predict, and learn behavioural responses, separating us from other species. This allows us to effectively navigate our environment- physically, socially, and emotionally.

At its core, the brain drives movement, whether that be in the form of a muscle contraction, excretion of digestive juices, or movement of thought. It is critical to understand the factors that influence brain development to understand its purpose. The brain is a fascinating organ and we are just at the brink of understanding some of its most intricate functions!

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