Why Do We Need a Brain?

The Self Illusion

How the social brain creates identity

Why Do We Need a Brain?

It turns out that we evolved brains for acting

Whenever I speak to the general public about the brain, I usually begin with a simple question, “Why do humans need a brain?” At first, this seems like a silly question with an obvious answer. “You need a brain to stay alive,” is the most common response and indeed this is true. You would be dead without your brain, which is why “brain dead” is usually the legal definition of death. Someone is brain dead when there is a lack of reflexive responses controlled by the brain stem, the most fundamental structures at the core of the brain that control the vital functions.

However, keeping you alive is not the sole responsibility of the brain. The same could also be said of your other major organs including the heart, liver and lungs. While it is true that these can all be successfully transplanted whereas a brain transplant is neither possible nor desirable (the topic of forthcoming blogs), it is not the case that to be alive depends on having a brain. There are many animals that are alive that do not have brains. They may have simple nervous systems but they do not have brains as such. There are even some animals that start off with a brain that they later discard. The classic example is the sea squirt that begins life as a tadpole-like creature, swimming around the ocean in search of a suitable rock upon which to attach. It has a simple nervous system to coordinate movements and even a rudimentary eye spot to “see,” but when it finally attaches to the rock, it no longer needs to move around and so digests its own nervous system.

That’s the answer to why we need a brain. The primary purpose of a brain is to move around our environment in a meaningful way. In fact, one could even argue that most of the brain is dedicated towards actions. If we consider that the basic building block of the brain is the neuron, then it comes as a surprise to most to find out that the majority of neurons are not in the association cortex where “higher” thought processes are generated. Of the estimated 86-100 billion, around 80% are to be found in the cerebellum, the bulbous structure at the base of the brain at the back that controls our movements.