The Whys and Hows of the Human Brains’ Evolution

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The Whys and Hows of the Human Brains’ Evolution

The human brain is the largest and most complex among the primate family / Photo by Denis Ismagilov via 123RF


When we study the different animals in nature, we find that their brains are often in proportion to the size of their body. Human beings, however, have brains that are six times larger than the expected size and that we have mental capacities more complex than any other animal.

Our enlarged brains have helped us to become the intelligent species we are now, and scientists have several theories as to why this came about.


The Cost of Intelligence

The human brain is the largest and most complex among the primate family. Between 2 and 6 million years ago, humans were beginning to walk upright and create simple tools. According to the Smithsonian, brain size was increasing very slowly over this time. From 800 thousand to 2 million years ago, humans began to gain more body mass, which subsequently increased brain size, as well. It was during a time of great climate change around 200 thousand to 800 thousand years ago when brain size was found to rapidly increase.

Human brains are a costly thing to maintain. This is no surprise considering that it has the ability to store several decades worth of information, process stimuli, and deliver a meaningful response in mere fractions of a second, and even allow the creation of abstract ideas and concepts, such as language and art. explains that brains take up only 2 to 4% of our mass, but they use up to 20% of all the body’s energy to keep running properly. Aside from that, larger brains mean larger heads, which causes painful births for mothers.

Nature and evolution often favor what would be more efficient and less energy-consuming, which baffled many scientists as to why we ended up like this, especially considering that thousands of species are able to thrive easily with small or even non-existent brains. It is a scientific consensus that brains got bigger in order to help humans solve the challenges they faced. However, what is unclear is what exactly those challenges were.


Prevalent Theories

For a long time, the prevalent theory was that sociological problems were the main reason brains grew in size. The reason this was the favored theory was that managing social relationships truly is a difficult feat for animals. Cooperating with others, managing a group in order to raid and hunt, and even anticipating the reactions of members of the group all required great levels of problem-solving. These dynamic problems then consequently caused brains to participate in an arms race that led to the large brains we have now.

The other major theory was that ecological problems were what pushed brains to become bigger. Being able to find and collect more food, store it properly, and even cook in an ever-changing savannah environment might have been the obstacles faced by ancestral humans. Their brains would have also given them a leg up in hunting and tracking prey, as well as creating fire.

Accepted Causes

Scientists have recently determined that it was more likely that ecological and not sociological factors were what drove humans to gain brain mass. They performed experiments and recreated scenarios with varying degrees of sociological or ecological challenges set up with a mathematical model. They then calculated how large the brains would get with each of these scenarios and kept track of how much energy would realistically be allocated to the brain in order to solve the problems.

They found conclusively that while a combination of both scenarios could recreate the size of human brains today, the ecological problems were the defining factor that caused brain expansion. In fact, sociological problems would actually decrease brain size. However, they also found that having a bigger brain wasn’t necessarily more advantageous. Having an absence of social problems could cause the brain to get bigger than it is now, but it would have been ill-suited to managing social interactions.


Why Only Humans?

It seems strange that having more social problems would decrease brain size, but it turns out that members of a group can solve such challenges by cooperating and putting their heads together. By banding together, problems can be addressed without having to create such a costly brain.

From 800 thousand to 2 million years ago, humans began to gain more body mass, which subsequently increased brain size / Photo by Maksym Chornii via 123RF


On the flip side, it is also strange that only humans have developed these large brains when many other species also experience several ecological problems that should’ve increased their brain size, as well. It was found, though, that humans only retained their brain sizes as they continued to learn and reinforce their acquired skills, especially as they culturally accumulated knowledge from their peers. Learning how to build a fire, hunt adequately, and forge better tools and accumulating this information eventually led to humans having to gain larger brains to store their knowledge.

Many scientists are still wondering whether or not human brains will still continue to change with more knowledge or interactions gained. It will likely take another several million years until measurable changes can be seen, though hopefully, such changes will be for the better for our species.



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