A Soulless Organ
The 600 Million Year Evolution of the Brain
When the ancient Egyptians mummified the bodies of their great pharaohs, all of the major organs were preserved, except for the brain. It was scooped out of the skull through the nose with hooks and thrown away because it was considered useless.
In ancient Greece, the flow of different fluids, or humors, in the body were considered vital for life functions. Aristotle thought that the soul lived in the heart since it connected all the fluids. Meanwhile, he believed the purpose of the brain was to cool the heart because it was “bloodless, devoid of veins, and naturally cold to the touch.”
For most of human history, the spirit or the soul was thought of as an ephemeral and immortal entity, separate from the prison of the body. It wasn’t until the 1950s that the brain started to reveal itself as home of the self. When the Canadian Dr. Penfield poked the brain of a live, awake patient, they were able to smell burnt toast. Somehow, the memory of that experience could be triggered just by stimulating that part of the brain.
While it is still unclear exactly how this happens, it seems that everything that we are, our experiences, memories, and knowledge all live in this cool organ in our heads.
But it wasn’t always this way. One of the earliest creatures with nervous systems didn’t even have a head.
The lancelet, or the amphioxus, is a tiny creature that lives in the water. It has a long and thin body with food that goes in one end, and a wiggly tail at the other to move around. It eats by burying its tail in the sand, facing upright like a blade of grass, to catch any food that happens to flow past the tip. It is basically a tube of cells that filters food out of the water.
Along this tube is a nervous cord running down the whole body from one end to the other, sitting on top of a stiff rod called a notochord. These nerves allow the creature to wiggle its tail in order to move and perch in another place. They also have basic photoreceptors to detect whether there is light or not.
The initial evolution of more complex nervous systems likely came about due to the pressures of predators. Once there was a threat of being eaten, it became important to detect and respond to incoming threats by having better senses, intricate movement, and more complex processing. It needed a brain.
The earliest known brains of vertebrates, animals with backbones, are found in fish that evolved from the humble lancelet. That simple notochord and nervous cord became the basis for the spine and the spinal cord we all have today. In every single vertebrate embryo, whether a fish, a lizard, or a primate, all start by forming a tube as it elongates itself. They all end up looking very similar to the amphioxus because of our connection in the evolutionary chain. What changed is that the tube starts to morph itself into bulbs that each becomes its own section of the brain.
Every single brain since has the same three main sections: the hindbrain, the midbrain, and the forebrain. The functions of each section generally remain the same. What varied as brains continued to evolve, is how prominent each section becomes.
The hindbrain forms the brainstem, the gateway from the spinal cord to the rest of the brain. It routes in much of the sensory information from the body and is involved in the management of vital organs, keeping the heart beating and lungs breathing. It also includes the cerebellum (“little brain”) that provides coordination of movement and balance. The midbrain further channels and processes sensory information. In non-mammals like fish, amphibians, reptiles, and birds the midbrain includes the optic lobes for handling visual information. In mammals, vision was shifted towards the more prominent forebrain, while the midbrain diminished in importance.
It is the transformation of the forebrain that began to dramatically change in mammals. It swelled from a relatively small bulb to a more dominant structure, making up the large round shape we usually think of. Some also changed from a smooth structure to one with many folds, increasing the area of the outer surface, or cortex, where its functional layers lie. This allowed more forebrain to fit into the same, limited space in the skull. It started to take up so much space that the other structures of the forebrain eventually tucked its way under the cortex until it was completely surrounded. These make up most of the limbic system that are involved in emotional regulation, hormone signaling, and memory encoding.
The evolution from the simple, tiny neural chords of the lancelet to the modern day human brain took over 600 millions years. This was when the Cambrian Explosion happened. It was a period when a large number of new categories of creatures started to emerge, creating a massive change in the variety of competition and interactions between animals. An evolutionary race was set off with whole new bodies and senses that needed the right accompanying brains to work with. Sea creatures grew mouths, eyes, fins, tentacles, claws, legs, and all kinds of new body parts. When they breached the land, they had to adapt to heat and dryness in direct sunlight, they had to change how they moved under gravity without buoyancy, and some eventually took to the skies filled with its own challenges. They all needed new ways to survive, find food, avoid predators, reproduce, and raise their young.
The brain came about out of necessity. More complex bodies and situations required a more complex understanding of the environment. It never evolved to understand language, tell stories, use tools, or invent new ones. It didn’t exist to study and analyze the universe to discover its secrets. The brain wasn’t meant to figure out how it works. It just worked. Yet here we are. The human brain, with the right tools, enough curiosity, millions of years of evolution, and thousands of years of knowledge, is starting to uncover the true nature of itself. It is no longer the mysterious, useless, cold, soulless organ it once was. It is the most incredibly powerful and complex self-learning, self-adapting system that has ever existed on Earth.
