By Jacob Andreae

Around 200,000 years ago, our brains stopped growing, and about 10,000 years ago, they actually began to shrink. The human brain is the most powerful “computer” on the planet. And it has modest beginnings. 

Where did it all begin?

The story begins in the oceans, long before animals even existed. Single-celled organisms didn’t have brains. But they did have advanced ways of communicating. They sensed and responded to their environment by releasing chemicals (which is slow) or shooting an electrical impulse across their body. 

From the single-celled choanoflagelletes that gave rise to animals 850 million years ago, the brain is now a 100 billion-celled organ. 

How did it all begin?

Choanoflagellates are single-celled organisms thought to give rise to animals. The nerve cells of ancient animals evolved long extensions known as axons. This enabled messages to be sent much more quickly as the chemical messengers only had to cross a small gap where the cells met, known as the synoptic cleft. 

Animals — most likely a worm-like creature known as the urbilaterian — began to develop groups of neurons. The most specialised neurons developed near the mouth and eyes. This group of neurons allowed information to be processed rather than just transmitted, and is the worlds first brain-like structure.  

A Brief History of the Brain

850 Million Years Ago

Choanoflagelletes give rise to animals. 

500 Million Years Ago

Things went wrong when one of our urbilaterian ancestors was reproducing, which resulted in its entire genome getting duplicated. This happened not once, but twice! These accidents paved the way for more complex brains by providing spare genes that could evolve in countless ways. 

360 Million Years Ago

Our ancestors colonised the land. 

200 Million Years Ago

Colonisation of the land gave rise to the first mammals. These creatures already had a neocortex. Extra layers of neural tissue on the surface was responsible for complex and flexible mammalian behaviour. 

65 Million Years Ago

We all know what happened here! After the dinosaurs were all but wiped out, some of the mammals took to the trees. The need for good eyesight led to the expansion of the visual part of the neocortex. 

14 Million Years Ago

The brain of ape descendants such as the orang-utans, gorillas and chimpanzees did not change much, except the apes who we descended from. We started to take a different evolutionary path to our ape cousins. 

2.5 Million Years Ago

Our brains began to grow bigger. It could be that a single mutation weakened the bite force, which before, had exerted a strong force across the whole skull, constraining the growth of the brain. 

2 Million Years Ago

The development of tools to kill animals led to a greater consumption of meat, which is rich in nutrients. This was essential in feeding the brain, which requires an enormous amount of energy, — burning about 20 per cent of our food. Fire played a similar role in allowing us to get more nutrients from our food, and allowing our guts to shrink, which also required a lot of energy to maintain. 

200,000 Years Ago

The modern human brain comes into existence in Africa. This was the peak in the size of the human brain to-date.  

10,000 Years Ago 

The size of the brain compared with the size of our body has shrunk by 3 to 4 per cent. 

The human brain has continued to grow in size since the single-celled choanoflagelletes gave rise to animals 850 million years ago. The human brain stopped growing in size 200,000 years ago, but evolution isn’t only about size. The brain might have stopped growing bigger (for now), but it will never stop evolving. Who knows what will happen in the future. The brain may become smaller and more efficient at using what it’s got, or it may start to grow in size again.

What do you think? 

Leave your answer to that question in the comments section below. 

Photo by Robina Weermeijer on Unsplash