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December 21, 2020

Unravelling the Mystery of Human Intelligence

The brain's evolutionary balancing act between storage, connectivity, data processing, and the free exchange of ideas.

Increasing brain size is credited as the key feature that propelled us from tree-climbing ape to space-traveling modern human. But is intelligence really just about an increase in brain mass?

Human intelligence has been shaped by the brain's delicate balancing act between data storage and data processing capability. But data storage can be outsourced. By talking to our friends and neighbors, reading books, doing a Google Search, or looking something up on Wikipedia, we've changed the rules of the evolutionary game so that memorization isn't as important as it used to be. It's creativity - finding useful patterns in the flood of data - that gives us an evolutionary edge in the modern world.

As a result, evolutionary pressure is gradually swinging away from data storage and towards more efficient data processing and more creative problem-solving. This is, quite literally, reshaping the way our brains are structured. Data storage capacity is falling. The wiring between different parts of the brain is increasing. And all that extra wiring is increasing the number of ways that we can combine data into new ideas. We may not be able to remember as many things as our ancestors could, but our brains are built to have more ideas, to be better at sharing those ideas, and to more easily build upon the ideas of others.

Brain Size in Our Evolutionary Family Tree

Meet the ancestors: Sahelanthropus tchadensis (7 Ma), Australopithecus sediba (1.98 Ma), Homo Georgicus (1.7 Ma), Homo Heidelbergensis (500,000 B.P.), Homo Neanderthalensis (60,000 B.P.), Cro-Magnon (Early Homo Sapiens, 30,000 B.P.), Homo Sapiens (7575 BC) , Apollo 11 - Buzz Aldrin on the moon (1969)

Our earliest ancestors had tiny brains, less than a quarter the size of our own. The closer we get to modern humans, the bigger our brains get. However, as the graph below demonstrates, there is a problem with our assumption that increasing brain size has followed us all the way from the trees to the age of space exploration. Starting about 30,000 years ago, our brains have been shrinking.

Hominid brain size evolution

Our ancestral cousins, the Neanderthals, had an average brain volume of about 1600 cm3. The brains of our own direct ancestors, the Cro-Magnons, were almost the same size. But our modern brains, with an average of around 1350 cm3, are more than 200 cm3 smaller! It took us 7 million years to go from 350 cm3 to 1600 cm3. And now we've lost the equivalent volume of a tennis ball in the last 30,000 years!

It's Neanderthals, not our own ancestors, who hold the top prize for the biggest brains. Yet they are extinct and we are still here, and thriving. We may have smaller brains, but we've created far more complex technologies and more robust societies (and we have a much higher standard of living) than Neanderthals could ever have dreamed of.

Clearly there is more to intelligence than brain mass.

Brain Size vs Intelligence

There is a strong correlation between brain size and intelligence when comparing ourselves to other animals. We even have bits that are either entirely absent or much smaller in other animal species, such as the neocortex, which is responsible for language, spatial reasoning, and conscious thought. More hardware does make a difference.

But this size-correlation breaks down between humans. If you and I get our heads measured, a measuring tape isn't going to be able to tell which of us has a higher IQ. And there is no evidence of any gender-based differences in intelligence despite the fact that women's brains are, on average, about 100 cm3 smaller than men's. Even the brain of one of the greatest geniuses of our species, Albert Einstein, was about 12% smaller than average. We know this because someone at Princeton University secretly removed, stored, weighed, and dissected Einstein's brain after he died, possibly without Einstein's permission.

Albert Einstein's brain
Albert Einstein's brain

Einstein's Brain

Einstein's involuntary brain autopsy revealed that his brain was not a cookie-cutter replica of everyone else's brain. Those differences can help us start to unravel the clues to human intelligence.

Some parts that are typical in most brains were missing in Einstein's brain, like his parietal operculum and his lateral sulcus. Other parts were bigger than normal.

His lower parietal lobe, for example, was 15% bigger than average. That's the bit involved in mathematics, visuospatial cognition, and being able to visualize movement - which happen to be the very exact skills that made Einstein famous. This region is also the part of the brain that functions as a sort of command center to simultaneously process useful information from multiple regions of the brain.

Einstein's brain also had far more connections between the two halves of his brain than what most people have. This connective tissue is called the corpus callosum. It is the equivalent of a bundle of fiber-optic cables that connect the two sides of the brain.

Corpus Callosum
The corpus callosum; the wiring connection between the two halves of our brains - Frank Gaillard, CC BY-SA 3.0

Grey Matter and White Matter

Our brain isn't just composed of little grey cells (grey matter). These cells also have to communicate with one another. For that we have a network of what is called white matter. The corpus callosum connecting the two halves of the brain happens to be the most dense cluster of these connective fibers, but there is a whole network of white matter throughout the brain. Here's what this network looks like in an MRI image:

white matter structure of the human brain
White matter structure of the human brain (taken by MRI) - Kubicki et al. CC BY-SA 3.0
One of the issues that autistic people face is that they are often missing key connections within their brains that link different regions together. Their grey matter is working just fine to store information, but there's insufficient communication between some regions of the brain so key information doesn't always get to where it's needed.

On the other hand, autistic savants, and people like Einstein, have unusually high amounts of connectivity between some regions so that certain types of information can simply be processed more efficiently.

Data Processing in the Brain

Faster information processing is more than just a function of being able to speed up how quickly data can be transferred between different brain regions.

The human brain is a lot like a computer. The grey cells are like individual little file storage centers. The white matter is like the wiring that connects all those files together so they can share information. But we also need a powerful data processing center that can juggle information from multiple files at once in order to put all that information to good use.

Simple memorization is merely a matter of retrieving information from one of these file storage centers. But imagination, insight, creativity, complex calculations, and even language skills all require the ability to simultaneously process information from multiple parts of the brain at the same time in order to re-combine it in new ways. The more wiring we have connecting all the different files stored in our brains and the more bits of information we can simultaneously retrieve from multiple files without overloading our neural networks, the more intelligent we will be.

The Ancient Evolutionary Pressures that Shaped Our Brain

Our brain size reduction over the last 30,000 years was most likely caused by an evolutionary shift towards more wiring (more and better-connected white matter) even as we reduced our file storage capabilities (less grey matter).

Neanderthal and early modern homo sapiens were hunter-gatherers. Storage of facts mattered. Their brains had to do the equivalent work of Google Maps and Wikipedia to find food, separate the edible from the dangerous, and locate shelter and waterholes along their migratory routes. In that lifestyle, there is definitely greater evolutionary pressure on memorization (file storage).

Yet despite the massive brain volume that Neanderthals had available for file storage, archaeological digs reveal subtle indirect clues about potential shortcomings in their wiring and data processing capabilities. They may have had a fantastic ability to remember all the different places where they stashed their nuts and seeds for the winter, but their trade networks were very limited; none of the material found in any Neanderthal toolkit (rock, shell, wood, etc.) ever traveled more than 200 km from it's origin. In other words, Neanderthals didn't like sharing.

By contrast, the materials used by our own ancestors during the very same time period provide evidence of trade networks that extended over thousands of kilometers. Trade goods must have changed hands many times along the way to travel such vast distances. That much complex social exchange requires overcoming the usual instinct of whacking strangers over the head.

While these differences can possibly be explained by mere cultural differences, it is more likely that these differences reflect fundamental differences in the intellectual toolkit available to each of our species. Social interaction requires very different intellectual capabilities than memorization.

If the wiring had been available, Neanderthals certainly had plenty of time (several hundred thousand years) and plenty of incentives amidst the rapidly changing ice-age climate swings to stumble upon a cultural strategy to allow them to increase information sharing and technological exchange. But they didn't.

Reacting to Ice Age Climate Swings

The way our two species responded to the changing enviromental conditions during the Ice Ages also reveals a great deal about our intellectual capacities. The Ice Ages were a time of extreme climate fluctuations that required very rapid adaptations to keep up with the ever-changing challenges posed by repeated warm inter-glacial periods and cold glacial surges. Memorization alone would not have been enough. With such rapidly changing conditions, survival depended on creativity.

Ice sheets periodically surged to cover the bulk of the Eurasian continent, leaving only a few small ice-free refuges, and then retreated again during the warm inter-glacial periods. Some of the temperature changes were truly extreme. In some cases, average annual temperatures plunged by as much as 7°C in only a few decades, turning lush forests into arid tundra and completely changing the wildlife species living in a region within the span of a single lifetime. To put that into perspective, the current warming period that is dominating news headlines today is expected to produce around 2°C of warming over a century. A truly modest affair by comparison.

Ice age climate fluctuations
120,000 years of Ice Age temperature and dust based on Antarctic ice core data - Vostock ice core petit, CC BY-SA 3.0

Neanderthals don't seem to have had the creativity to cope with these rapid changes. Archaeology demonstrates that with each glacial surge, Neanderthal population ranges were reduced more and more. They simply didn't repopulate all their former territories after the ice retreated. With each fresh glacial surge, one by one, Neanderthal populations were snuffed out as they failed to adapt to the rapidly changing ice age climates. By the time our ancestors arrived in Europe 45,000 years ago, Neanderthal populations were already in steep decline.

Our own ancestors fared much better. Archaeology shows how rapidly our own ancestors invented new technologies in response to these fast climatic changes and, thanks to their extensive trade networks, how fast these new ideas spread throughout the whole population. Each time the ice retreated following a glacial surge, our ancestors' population numbers bounced back even stronger than before.

Our ancestors were good at innovating. Individual Neanderthals may have been too. But our ancestors also were good at spreading their ideas so that no single small tribal group had to individually come up with all the innovations needed to survive. Among our own ancestors, as long as someone in their vast trade and social network came up with a useful idea, everyone else could benefit from it (and build on it). 

Creativity depends on having access to lots of ideas, and not just our own ideas but also those of others. The ability to adapt quickly to a rapidly changing environment requires harnessing far more ideas than any individual or family can generate on their own. It is the efficient exchange of ideas that allows individuals to draw upon innovations from well beyond the immediate tribe. Welcome to the sharing economy...

Imagine how much slower the rate of innovation in our modern society would be if Princeton University had kept all of Einstein's research locked up so it could never be seen beyond the campus boundaries instead of publishing that research in print (and now on the internet) for everyone else to see around the globe.

Our ancestors' brains seem to have given them an advantage compared to our Neanderthal cousins - not only did our ancestors have lots of creativity, but that creativity was combined with increased social interactions to allow ideas to spread quickly. Exchanging ideas, whether through trade, warfare, or campfire visits, is a complex intellectual activity that involves multiple regions of the brain that must work together simultaneously. The exchange of ideas simply does not work efficiently without lots of white matter connecting all the various brain regions together and a powerful data processing center to crunch the data.

Based on brain volume, we have less fact-storage capability than the Neanderthals did, but it seems that we won the race 40,000 years ago because we had more wiring to both recombine information in new innovative ways and because we were wired to spread those ideas quickly through social interaction.

I would bet that if we could scan a Neanderthal brain in an MRI machine, we would see a lot less white matter in their brains than in ours. Unfortunately, there aren't any Neanderthal brains that have survived inside any of the skulls we've found... so far. But perhaps, if we're lucky, we'll find a frozen Neanderthal in a glacier or in the permafrost, much like we've found a few frozen mammoths and frozen woolly rhinoceros from that era with all their soft squishy bits still intact.

Hardware Limitations - The Delicate Balancing Act of Brain Evolution

Relying on internal memory storage is extremely limiting because there is only so much space inside our skulls. As long as our heads have to fit through our mother's pelvis during birth, there are physical limitations to how big our heads can get. Perhaps Einstein's brilliance in certain areas was only possible because some parts of his brain were underdeveloped, which provided the space for other areas of the brain to grow bigger.

However, volume limitations are the least of our problems. Overcoming the limitations of our wiring and data processing capability pose a far greater challenge.

More storage capacity requires a larger network of wiring, without even expanding the wiring to any individual group of cells within the brain. It's like building a larger house that has more rooms. It takes more wiring to service all those rooms, even if each individual room doesn't get more light fixtures or electrical sockets than the rooms located in smaller houses.

Whenever we increase the wiring inside our brains (either because we add storage capacity or because we increase the amount of wiring leading to any individual region of the brain), this comes at a cost. More wiring means we need more data processing capacity to keep up with the extra volume of information being generated. 

Unless the data processing center expands to keep up with all the extra information being delivered, adding more file storage or increasing the wiring to those file storage centers means that neural networks overload sooner, leading to less creativity and less innovation, not more. Classic information overload.

Data processing capacity is the limiting factor in this equation. Consider the number of ways that you can combine data from two separate data sources, A and B. There are only two possible ways to combine them: AB and BA. Add data from a 3rd source, C, and suddenly the possibilities for full and partial combinations increases to 12: AB, BA, AC, CA, CB, BC, ABC, ACB, BAC, BCA, CAB, and CBA. As the volume of data sources (wires or grey cells) increases in a linear fashion, the number of possible ways to combine and recombine that data into new ideas increases exponentially. Even the tiniest increase in data volume requires a massive increase in data processing capability.

This is the balancing act of brain evolution - the delicate equilibrium between information storage, wiring/connectivity, and data processing capacity. A gradual increase in data processing capacity is simply not going to keep up with exponential increases in data volume. So, it seems that over the last 30,000 years we have trimmed storage capacity to compensate for an increase in wiring in order to protect our rather limited data processing capabilities against overload.

Yet we certainly haven't suffered as a result of shrinking information storage capacity. We've found a rather tidy data storage solution that more than makes up for the difference...

Storing Data in The Cloud

We've overcome our individual data storage limitations through external data storage.

First we increased our social interactions with other members of our species (through trade, war, and campfire visits), which allowed us to access information stored in other people's brains without having to remember everything ourselves. This freed up more space for more wiring, which in turn has led to greater innovation.

Writing and the invention of books were the next big leap forward, allowing information to travel vast distances, independent of the writer. Books even broke through the barrier of time, allowing ideas from inside any one person's head to survive in the pages of books long after the writer has died. But monks copying books by hand in the dusty corridors of tightly regulated cloisters was a slow and inefficient way to spread information, which was further obstructed by the heavy hand of censorship filtering the information that was allowed to trickle out beyond the cloister walls.

We broke through those data storage limits and unshackled the free exchange of information when we invented the printing press, which allowed us to easily store and share information on a massive scale. The tremendous creativity of the industrial revolution probably wouldn't have happened without industrial-scale information-exchange made possible by the printing press.

And now we've invented the internet, which allows us to store and access information on an unprecedented scale. Yet all that new storage is external - outside the brain - which makes it far more reliable (it doesn't corrode over time like working from memory) and it's much faster to retrieve (thanks to Google Search) than trying to remember everything ourselves. In fact, the volume of information is so vast that digital memory has even moved off individual computers and into the cloud in order to expand the efficiency, reliability, and range of our data storage capability.

Like the industrial revolution before it, this new information revolution is triggering a huge surge in innovation and creativity and has sparked the development of countless new technologies. The World Wide Web is only 35 years old; imagine where we'll be in another century! Yet it's all happening without any increased storage capacity in any individual brain. In fact, it's happening against a backdrop of decreasing brain volumes!

With the whole of Google Maps, Wikipedia, and the entirety of human knowledge available at the click of a mouse or the thumb-swipe of a smartphone screen, we've effectively outsourced our information storage needs.

CERN data center
CERN data center - Hugovanmeijeren, CC BY-SA 3.0

In essence, Google and Wikipedia have made file storage irrelevant. If anything, greater storage capacity is as much a liability as an asset. A smaller brain volume means less wiring is required to provide basic services to the whole brain, which reduces the flood of data noise reaching our data processing center. This makes our data processing center more efficient and more creative because it frees up resources to focus on processing the targeted data that we deliberately choose to feed into the system whenever we pick up a book, read a new article, or do a Google Search.

So, rather than increasing our grey matter (file storage), the next phase in our brain evolution is most likely going to favor an increase in the amount of white matter (wiring) interconnecting our little grey cells and an increase in our data processing capability. Even if our brains don't get any bigger (or even keep getting smaller), they're probably going to get denser, more efficient, more creative, and more capable of processing large volumes of data!

But what happens next isn't just a question of submitting to the evolutionary pressures acting on each subsequent generation. We also have a huge amount of power to shape those forces, not just on a societal level through the technologies that we develop and use, but also on an individual level, within our own lifespan, based on how we use our own brains every day.

Nature vs Nurture

Some people, like Einstein or autistic savants, are born with more little grey cells in certain areas of their brains or a little more white matter connecting different regions together. This certainly predisposes them to greater talents to perform certain skills compared to their peers. But even Einstein's brain was not a fixed entity. He literally changed the shape of his brain as a result of how he used it.

Einstein's larger parietal lobe predisposed him towards greater mathematical skills, but the more math he did, the bigger his parietal lobe got. We know from MRI scans that musicians show enlarged regions in certain parts of their brain corresponding to both the music processing skills and to the physical motor skills that are unique to each instrument. Multi-lingual language learners will physically enlarge different regions inside their brains as they broaden their language skills. Even the smart-phone has changed our brain structure, leading to an enlargement in the region corresponding to thumb dexterity - all because we use our thumbs to type on our phones!

MRI scans show that these changes in brain structure are caused by increases in both grey and white matter within the affected regions, as well as an increase in white matter between different regions of the brain that have to work together to produce each of these skills.

In other words, neither the grey nor the white matter inside our brains is fixed. Our brain is continually shaped and reshaped by how we use it, much like our muscles are shaped by their use.

Practice Makes Perfect

Unfortunately changes in the brain work both ways. If we don't use certain parts of our brains, those parts tend to whither away. Use it or lose it. That's why learning new things and challenging our brains are strongly suggested as a defense against age-related illnesses like dementia. 

Every hobby we learn, every new idea we expose ourselves to, every skill we practice, and every new challenge we undertake will change the very fabric of our brains. 

Not good at something? Practice. The more we do something, the more we increase the wiring (white matter) and the file storage capabilities (grey cells) in the corresponding parts of our brains, allowing us to outgrow inexperience, repair damage after a brain injury, and overcome developmental deficiencies. Just because some paths to intellectual greatness are longer than others doesn't mean that any of us have to settle; we just have to keep practicing, practicing, practicing as long as it takes. The wiring and the little grey cells inside our brains will grow with us along the way. 

Which means that the evolution of human intelligence is not just a function of changes to how our brains are structured, but is also about the cultural habits we adopt, both as individuals and as a society, to practice specific intellectual skills. (Or whether we let our intelectual capacities go to waste by spending all our time on the couch watching soap operas).

Individual vs group intelligence

Intelligence isn't only about what happens inside our own brains. Equally important is how easily our brains can access the data stored in someone else's brain, even in the brain of some stranger whom we've never met. Lack of trust, a debilitating suspicion of strangers, or an unwillingness to seriously engage with unfamiliar ideas and opinions are not intelligent survival strategies, no matter how brilliant we are at solving our own familiar problems. That's precisely what caused Neanderthals to lose the race - they didn't share; each tribe tried to do everything themselves. Second place in this race earned them an honorable mention in the history books, nothing more.

A few hundred thousand years of minimal information exchange (evidenced by their limited trade networks) suggests that Neanderthals lacked the wiring for more widespread sharing of ideas and technologies. They were trapped by the wiring inside their own heads, unable to make the leap beyond the thoughts and beliefs contained within their own heads and the heads of their immediate group.

We, on the other hand, have demonstrated that we have a remarkable talent to plug into the minds of other people, allowing us, as a group, to overcome our individual limitations and harvest ideas from strangers, even when we don't like one another.

But only when we choose to.

Scientific knowledge, technology, and improving standards of living have grown relentlessly since Neanderthals died out around 40,000 years, but it has not been a smooth journey. It is littered with "dark ages" during which progress stalled or even reversed, sometimes for centuries at a time. Those reversal periods are dominated by individuals, cultures, countries, and belief systems that feared strangers, rejected new technologies, suppressed free speech, restricted the rights of some members of their society, and put excessively strict limits on the movement of people and ideas across borders.

Our intelligence depends on being exposed to the ideas inside other people's heads. The fate of the Neanderthals is a stark reminder that close-minded cultural beliefs, isolationist attitudes, and social bubbles are the evolutionary equivalent of a Neanderthal's 200 km trade network. These are not winning survival strategies because they artificially impose limitations on information exchange. Self-segregation is a form of intellectual starvation.

When times are toughest, we are often tempted to put limits on the free exchange of ideas. Protectionism, government control, and central planning always surge during times of crisis. When we feel threatened, whether by war, famine, economic collapse or a viral pandemic, our instinct is to put limits on individuals and hand over power to a small circle of central planners who have the power to control innovation and put limits on the exchange of information and ideas between people.

Yet our ability to adapt and find solutions to our problems depends on our ability to stay open-minded, to wrestle with the ideas of our greatest skeptics, to continue challenging our most firmly held assumptions about the world, and to unleash the free flow of information and ideas between people. This is not the easy route. It requires huge amounts of self-awareness to resist our impulse to control the world around us when we feel most vulnerable. But thanks to the malleability of our brains, the more we practice this skill, the more we'll grow the grey cells and white matter needed to make this skill easier so we can continue to successfully adapt to the world around us.


So, the story of human intelligence is not just a story about striking a balance between data storage, wiring, and data processing capability. Human intelligence is just as much about the exchange of ideas between brains. 

It turns out that intelligence is a shared process, an open-source evolutionary experiment unlike anything that our 4.5-billion-year-old Earth has ever seen. And where it evolves from here depends entirely on what we choose to put inside our brains, what tasks we set for ourselves to challenge our brains to new horizons, and what beliefs and cultural attitudes we adopt to either restrict or unleash the free flow of ideas between people. How we shape our minds is up to us. No other species has ever had such control over its own evolution!


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