Brain Size and Human Evolution

Let’s start off by getting something out of way immediately.  We use a 100% of our brains everyday all the time even sleeping.  The 10% thing is a myth and not even close to being correct.  However, it is a pretty well believed myth.  In 2013 a survey showed that 65% of Americans believed we only use 10% of our brains.  There is a lot speculation about how the 10% thing got started and nobody knows for sure but it just isn’t true.  Testing of the brain while awake and sleeping show we use 100% of our brain all the time.  So, if you are waiting to tap into that vast 90% brain reserve to accomplish the spectacular achievement you have been dreaming about you might be better off just rolling up the sleeves and getting to work because you are already there.

10% of the brain use

Not sure if this is related or not but 47% of Americans believe in Aliens and 39% believe they have visited Earth.  I am by no means trying to ridicule the idea of intelligent life elsewhere in the universe.  I actually believe there is life on other planets and there is intelligent life elsewhere too, the possibility seems real to me.  I just don’t think they have been using Earth as a vacation spot.

Hey, I like SYFY as much as the next guy.  I just don’t think we need to step away from ourselves to explain any aspect of hominin achievement down through the human legacy.  There just aren’t select individuals using 100% of their mind while the rest of us languish in the mire of running on 10% brain power.  By the same token every technological advancement isn’t because some Ancient Alien was kind enough to help us poor 10% brainers out.  The story of human consciousness and the mind is so wonderfully fantastic and complex it far, far eclipses any fictional representation of how evolution unfolded. 

 Advances in life and especially technology sometimes do seem so miraculous that we can’t accept the credit for ourselves.  Advances kick us out of our comfort zone especially when they come quickly.  I think there is a propensity to ascribe the impetus for these changes to forces other than ourselves.  But the truth is the human mind and consciousness is miraculous in itself and delivers to us a steady stream of miracles, albeit human nature to accept the miraculous as commonplace when we are surrounded by it our whole lives.

first plane flight
First plane flight December 17, 1903

In 1900 planes did not exist.  Now hundreds of millions people fly all over the world every year. It’s very common place, so much so that we don’t give it second thought.  It’s a staggering intellectual and engineering achievement.  We can watch events unfold in real time on the other side of the planet on big screen tv’s.  We can see and talk to each other all over the earth in real time on smartphones.  We can put our butts in an automobile and drive 80 miles an hour down the interstate listening to music via satellites while enjoying the air conditioning on a hot day and if we feel like it make a hands free phone call to anywhere in the world.  We can successfully transplant body organs out of one human being and put them in another, even the human heart.   

All of this and way more is so commonplace we hardly ever give it a thought but really, what the hell is going on here?  Have we walked into a different dimension in the last hundred years?  Has the entire human race been transported via some SYFY mechanism into a universe where the miraculous seems common?  The time traveler from 1900 would think so.  What in our world could be more common and mundane than electricity.  Ask that to the 1900 time traveler who did not have electricity or even indoor plumbing.

H. G. Wells book the Time Machine

You want to talk wealth?  We’ll talk wealth.  Here in America we can jump in the car and drive to the local grocery store and buy the ingredients for dinner from all over the world.  Vegetables from Chile and seafood from the Mediterranean, spices from India and Africa, and a variety of food stuffs from every part of the world.  It is all fresh and ready to consume.  The time traveler from 1900 could not do that even if he or she was the wealthiest person on earth.

It is estimated that if you are a family making 70,000 a year today you are far wealthier than a family making 700,000 a year in 1900 that lived in a mansion with dozens of servants.  Just think of the everyday conveniences we have now that were not even invented then and that’s not to mention the healthcare.  People died all the time from things we cure routinely.  

The things, the devices and circumstances we live with were unimaginable in 1900. A miracle is the only way to describe what we have available to us today.  A miracle courteous of the ingenuity derived from the human consciousness and the mind. 

I know what you are thinking right now.  If that’s the case why didn’t Neanderthals kick back 500,000 years ago and watch a good football game or romantic comedy on their big flat screen tv?  I mean after all they had the same size brain as we do, many think even bigger. If brain size is the main indicator of cognitive ability it does seem like a reasonable question to ask doesn’t it? 

Well in one of those ironic twists, all the major achievements we’ve had in the last 100 years was accomplished in spite of a 10% shrinkage in brain size.

In the last 20,000 years the human brain has shrunk 10% in size.  If the brain keeps shrinking at the same rate in another 20,000 years we will have the same brain size as Homo erectus did 1.9 million years ago.  How weird is that?

shrinking brain size

Does this mean we are getting dumber? It certainly does not seem that way.  Seems like we are getting smarter.  Maybe there are other forces at play other than the sheer size of the brain that influence cognitive ability.  A good answer to this might be that the brain’s wiring and chemistry has changed in the last 20,000 years to facilitate a smaller more efficient brain size yet an increase in cognitive ability.    

To better understand let’s take a closer look at the thing.

The average human brain weighs in around 3 pounds which is about 3% of the body’s weight.  However, at only 3% of body weight the brain uses 20 percent of the body’s energy.  The vast majority of the energy used by the brain is for the billions of neurons communicating with each other all the time.  There are 86 billion neurons in the brain, each connected and cross connected via synapses numerous times.

the human brain

Most of the brain mass is contained in the cerebrum and where all the higher cognitive functions take place.  Then you have the cerebellum and the brain stem that takes care of the rest of the bodily functions. 

The functioning of the brain is accomplished by electrical and chemical firing between the synapses which requires energy all the time.  The next picture represents the chemical and electrical exchange of information between synapses. 

synapses in the brain

The brain is comprised of 86 billion neurons.  Imagine 86 billion neurons all with multiple synapses and connections, it must be in the trillions of combinations.

The cerebral cortex is the largest region of the cerebrum.  It is the outer layer and called the grey matter.  This is where the cognitive abilities are located.

The next photo is a look at a cross sectional slice of the cerebrum, a dye has been injected which enables you to see the cerebral cortex easily.

cross section of the brain showing grey matter.

The human cerebral cortex contains 16 billion neurons, there are 69 billion in the cerebellum and about a billion in the rest of the brain.

Cognitive Ability

 Humans clearly enjoy the greatest cognitive ability of any species on earth, by a long shot too.  How does cognitive ability relate to brain size?  The larger the brain the higher the cognitive ability, right?  Not really.  Elephants and blue whales for example have much larger brains that we do so actual brain mass does not indicate level of intelligence.  There have been tons of experiments with different animals ranging from rats to elephants in an attempt to understand cognitive ability and how that has developed. 

The elephant has a brain mass three times the size of humans and it has 257 billion neurons compared to our 86 billion neurons, again three times the amount.  However, the cerebral cortex of elephants contains 5.6 billion neurons compared to the 16 billion neurons of humans.

It turns out that the number of neurons in the cerebral cortex is a benchmark for cognitive ability and as humans we have more neurons packed into our cerebral cortex that any other animal.  Or do we?  Pilot whales actually have more neurons in their cerebral cortex that we do.  Does that mean they are smarter than we are?  No, they are not smarter than we are.  What it means is we do not definitively know the entire answer to this question but surely the number of neurons in the cerebral cortex is the best indicator of cognitive ability we have so far. However, there are other considerations besides the actual sheer number of cells. 

In my opinion there is something above and beyond the actual physical properties of the brain that separate humans from the rest of animal life on earth and that something lies in the human consciousness.

The evolution of the human brain size.

You would think on the surface of it that the human brain keeps getting bigger and bigger.  However, the reality of it is we topped out about a million years ago with Homo heidelbergensis.

There was a lot of growth in brain size between the Australopiths and Homo erectus but not much after that except for the Neanderthals.  Part of the reason for the larger Neanderthal brains can be attributed to the fact that individuals in colder climates have a larger brain size.  I am not trying to take anything away from the Neanderthals but their larger brain size is also a result of having larger eye sockets and a larger area of the brain devoted to sight.   If you take out the visual area of the brain from both Neanderthals and Homo sapiens then Homo sapiens actually have a bigger brain area left.  Just saying.

When you look at the graphic above you can see that Heidelberg Man had roughly the same size brain as we do and that was not much bigger than Homo erectus, about 15% bigger in fact.  A general consensus for a timeline to Heidelberg Man is 800,000 BCE but I would push that back to 1.2 million years ago based on some fossil finds that could be them.

So as a rough estimate, hominins have had the same brain size for a million years but only drive-thru fast food since the 1950’s.   Surely there is some sort of reason for that.  You would think that if brain size alone was the main contributing fact in cognitive ability it wouldn’t take a million years to develop smartphones and the internet.

It is pretty much impossible to study the brain tissue of ancient man.  The oldest known brain tissue discovered is roughly 2,500 years old.  And that doesn’t mean it could be analyzed to any extent.  Certainly not to the extent of determining neurons in the cerebral cortex.  So, we are left to speculate about early cognitive abilities by studying the circumstantial evidence uncovered with the archaeological record.  Fortunately, Anthropologists being the clever and resourceful scientists they are have built up quite a bit of knowledge about the cognitive abilities of early man. 

Early hominins from Homo erectus on were not dumb brutes milling about grunting and grubbing out an existence.  They had a culture which included art, music, body adornment, sophisticated tools, clothing, shelters, domesticated fire, commerce, language and symbolic behavior.  However, as advanced and impressive as their cognitive abilities were they still could not make the leap beyond hunting and gathering tribes.  As sophisticated as their ability was to create culture they still lacked the ability to wrap their head around making larger social constructs.   Between where they were, and when I say ‘they’ I am throwing in archaic Homo sapiens too, and where we are now, something in the mind and consciousness changed.  And this change was momentous.  It is the single most significant event in the hominin line in the last one million years. Had this change not happened we would still be in hunting and gathering tribes, while not a bad life style at all… no internet.  Yikes!

Toba Debunked

It is safe to say that at some point in the past the cognitive prowess of H. sapiens reached the point where we could develop the culture constructs and have the intellectual ability we have today. All evolution starts with mutations in the genetic code in the DNA of individuals of a given species.  The vast majority of mutations are neutral and do not have much effect.  Some mutations are detrimental to the species and are breed out thru the process of natural selection.  Some mutations are beneficial to the species and are kept and improved upon thru the process of natural selection.


There is no doubt that mutations influencing the way the brain functions took place, irrespective of the size of the brain. This mutation or series of related mutations created a greater number of neurons in the cerebral cortex than ever before. These mutations changed the way the brain synapses functioned and enabled humans to achieve a greater and greater degree of cognitive ability. 

These mutations happened over a period of time incrementally contrary to a popular notion called ‘The Toba Effect’.  The Toba effect refers to the Toba supervolcano in Indonesia that exploded 70,000 years ago.  It was the biggest explosion in the last 2.5 million years and created what is called a nuclear winter that lasted for years.  Or did it.  New research has revealed that the earth recovered more quickly than previously thought.  In addition, it is now known that there was no bottleneck effect on human evolution from a precipitous drop in the human population due to the eruption.  (With a small number in the population of a species, evolutionary changes can occur very quickly – a bottleneck effect.)

volcano eruption

It has been discovered that there was no appreciable nuclear winter in East and South Africa and people there coped rather well with the effects of the eruption.  Even in India the event had no disastrous results.   It had been speculated that the Toba eruption initiated a ‘cognitive revolution’ in humans resulting in the expansion of Homo sapiens range and their takeover of the planet.  However, this view is no longer widely accepted given the recent discoveries and analysis of the Toba eruption.  This coincides with other recent archaeological finds proving advanced cognitive ability way before the supposed ‘cognitive revolution’.

The mutations that created the changes in the physical reality of the brain and how it functions also created changes in the mind.  I believe the mind is a separate entity from the purely physical brain.  The changes in the mind allowed for the expansion of consciousness.  I also believe that consciousness is a separate part of our being.  It is the changes in the consciousness that created who and what we are today.

This is the second post in a series explaining the evolution of human consciousness and what that means for us as individuals as well as collectively. The first post is here.  

Before we move on though there is one more critical step involved that I need to go over in the development of the human brain.  As I have already said, the human brain has not gotten much bigger in the last million years and really not a whole bigger in the last 1.9 million years since Homo erectus came on the scene.  Before that the Australopiths brain size was between 400cc and 500cc.  Then it jumped up two and half times with H. erectus.  What happened there?  Well it’s a very clear story.

This is probably not a good story telling technique but I will give you the punchline first.  Fire.

So here is basically the deal.  When the early hominins did not have a cooked diet, they spent most of the day foraging for food.  Like about 80 to 90% of the day looking for and eating raw foods.  When you look at how the great apes feed today you can see that.  They spend over 80% of the day eating to support their body.  They have to spend that amount of time searching and eating raw food because it takes that much time and raw food to give them the energy from the food to sustain them.  And that is with the small brain size they have.  A gorilla will spend up to 8 or more hours a day foraging and eating food.

gorilla eating

By the same token if a human had to live on the same raw food diet, we would have to spend 10 or more hours a day eating to support our body and large brain size.  Remember, 20% of the energy we use is for the brain alone.

With the domestication or harnessing of fire H. erectus was able to cook its food.  Cooked food has a greatly increased caloric yield because of a greater ease of chewing and also the digestion and absorption of the food eaten became easier on the body.  Even when you consider eating raw meat was probably part of the Australopiths diet, raw meat is difficult to chew and digest, but cooked meat is way easier to chew and has a larger caloric yield.  Besides, and this is not being facetious, cooked meat and other foods just taste better on the grill or open fire. 

Cooking food gives a much higher caloric intake which means H. erectus had more time on its hands for other things like social interaction and tool making and just plain figuring out stuff to make their lives better.  These sorts of activities also created a positive pressure for a bigger brain size.  And this extra energy was acquired by not by a radical new diet but by eating the same diet just having cooked it over the fire.

The domestication of fire and the cooking of raw foods over fire is the single biggest event in the increase of hominin brain size.  The increase in brain size resulted in the increase of the neurons in the cerebral cortex resulting in greater and greater cognitive abilities. 

The Cognitive Milestone

As big of a milestone that cooked food represents for our evolution there is an equally big milestone in cognitive development in the expansion of consciousness past a certain threshold that enabled modern man to become modern man.  This threshold was not dependent upon brain size or Homo heidelbergensis would have had smartphones.

 The crossing of this threshold in consciousness was not dependent on any activities that were required for survival and the harnessing of environmental resources.  From Homo erectus onward, the hominin line was very well equipped cognitively to survive in the world they lived in.  This expansion of consciousness was facilitated by the changes in the brains wiring which gave fertile ground for growth to activities that we define as being fully modern man.  They are symbolic behavior and use of symbols, social interactions, complex language, creating art, creating music, body adornment and participating in ceremonies both civil and spiritual.    These are the activities that expanded the mind and added more neurons to the brain. 

We may never be able to point to a date, even within ten thousand years, that identifies the time when the expansion of consciousness for H. sapiens crossed the threshold from archaic to modern man.  However, the factors pointing to that time period will be better understood by the archaeological discoveries with regard to the activities of symbolic behaviors, art, music, body adornment and the civil and spiritual ceremonies exhibited by modern man.

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Jay Boyle

Very interesting and well written. Keep it up.

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