The Incredible Shrinking Brain

Our brains are shrinking. A recent study done by a group of paleo-anthropologists from the University of Wisconsin has found that the average human brain today is significantly smaller (200 cubic centimeters) when compared to the average human brain during the paleolithic era. (McAuliffe, 2011)

Before we dive headfirst into this problem, let’s look at evolutionary theory behind the human brain. Our brains are big. Some are bigger than others, but as a species we’re doing pretty well for ourselves. And good thing too. Of all the varieties of man to walk the Earth (Homo habilis, Homo florensis, Homo neanderthals, etc.), anatomically modern Homo sapiens (us) are by far the weakest and puniest of the group. We definitely would be picked last in any inter-species kickball game. To illustrate just how physically inferior we were to our competing genus, Neanderthals would have been able to pick up an average sized modern human and from a stationary position, toss us twenty yards through football goal posts. (Haviland, 194)

Then how is it possible that we could thrive while the others only exist in obnoxious car insurance commercials? Our advantage is our intellect. Our brains are proportionally larger to the rest of our body mass when compared to almost all other hominids (with the exception of Homo neanderthals whose brain size was comparable to ours but lacking in some important areas). (Pearce, 2014) The most significant difference between our brain and other animals is the region known as the “prefrontal cortex”. Considered the “CEO of the Brain”, this region controls higher level thought processes such as: creative thinking, abstract reasoning, planning, logic, and perhaps most importantly, complex problem solving only really found in Homo sapiens. This is what gives us the ingenuity to not only adapt to our environment (by doing things like putting on more clothes when it gets cold out or developing shelter for when it rains) but also the ability to adapt our environment to fit our needs (invent irrigation to make unfertile land more arable). This ability to problem solve by adaptation is what allowed us to survive in an ever-changing environment.

This evolutionary strategy may have seemed like a “no-brainer” (pardon the pun), however it was actually quite the gamble. These massive brains of ours have a tremendously high energy cost. This one organ burns through roughly 1/5th of our daily consumed calories (roughly 300 to 400 calories a day). (Adler, 2013) In the calorie-scarce world of Paleolithic era, many other hominids took the evolutionary course of making themselves bigger/faster/stronger in order to make themselves more capable hunters. We departed from this course, making ourselves smaller/slower/weaker. This tradeoff takes calories away from our body’s ability to smash and stab things and reallocates them to our brain’s ability to solve and adapt to a wide ranging variety of problems.

Intellect alone was not enough for our early ancestors to triumph over their prey. This is where technology comes in. The use of tools and technology is pretty much the sole domain of the human branch of the animal kingdom (some apes have been observed smashing nuts with rocks or using sticks to pull ants from their hills, but this behavior is the exception rather than the norm). Our Paleo-ancestors learned early on that their hands alone would not be effective in taking down animals large enough to feed entire tribes.

Early technology was extremely simple yet effective. The spear for example was designed to not only help inflict mortal wounds to their prey but also allowed hunters to do so from a safe distance. The paleo-learner developed technology to aid in many things such as: hunting, creating fire, producing shelter in a variety of habitats, and carrying large quantities of berries from where they were gathered to where they would be consumed. Those, and all necessary daily activities required a great deal of ingenuity and creativity.

Paleo-technology is derived from the human intellect. When paleo-learners encountered new problems, they used their advanced critical thinking skills to develop improvements to their technology. Early hunters made enhancements by adding a spear thrower. This tool was a strap on the wrist that extended outward so as the thrower thrust his arm forward, it increased the length of his “arm”. This resulted in increasing the velocity at which the spear was thrown and the problem of a hand-thrown spear not being able to pierce the thicker hides of larger game animals was solved.

Therefore in a theoretical world where people start with 0% technology, people would depend on 100% of their intellect and problem solving skills for survival. This would be a world in which people’s very existence would require them to invent and develop technology in an attempt to solve the problems they would encounter.

Because humans spent close to 200,000 years in the in the calorie scarce world of the Paleolithic era, evolution has sent us on a path of calorie conservation whenever possible. Seeing how our brains are the largest consumer of calories in the human body, when intellect is no longer required for survival the body adjusts by decreasing the calories allotted for it.

A similar trend is seen with the domestication of animals. Wild animals and their domesticated counterparts are genetically identical. It doesn’t take a scientist however to see the differences between a wild boar and its domesticated counterpart, the pig. Besides being hairier, having a longer snout, and tusks, the wild boar also has a much larger brain. This is because a wild boar has many more challenges and problems it faces for survival on a daily basis. It is on its own for acquiring food and for avoiding natural predators. Domesticated pigs have someone else attending to these problems for them. Because the domesticated pig no longer needs to solve problems critical for its own survival, it no longer needs to allocate important calories to its already limited intellect. Therefore, there is a corresponding decrease in the size of the animal’s brain once it becomes domesticated. Almost every single domesticated animal has a significantly smaller brain than its wild counterpart. (McAuliffe, 2014)

Like domesticated animals, today we no longer rely on our intellect for our survival. Our critical needs: food, water shelter, etc, are already taken care for us. It doesn’t take too much cunning to pick up a couple pounds of ground beef from the grocery store. Any problem we do encounter, we depend on technology to solve for us. As technology evolves and problem solving for survival becomes less, there become fewer pressing problems (problems in which life depended on its resolution) to solve. Technology has become the equivalent of our problem solving farmers of the animal world.

As the greatest mind of the 20th century, Albert Einstein, predicted, “I fear the day technology will surpass our human interaction. The world will have a generation of idiots.” The main difference between the technology of the paleo-world and the modern-world is that today’s technology acts to replace intellect rather than stimulate it. From calculators, MapQuest and other GPS devices, to search engines, technology is increasingly designed to do our thinking for us. Therefore in a theoretical future where we have turned 100% of our problem solving needs over to our technology, there will be 0% need for intellect.

If this theory and comparison to domesticated animals were to prove true, you would expect to see a gradual decrease in the size of the human brain the further removed our intellect is from our own survival. And sure enough, studies done comparing the brain size of Paleolithic people to the modern person have shown an average decrease in size of about 200 cubic centimeters (roughly the size of a tennis ball) in the modern human’s brain. (McAuliffe, 2014) Evolution has responded to our diminishing need for intellect by decreasing the size of our brain so that it may conserve calories.

In fact, several studies have shown actual brain atrophy in young people with an overdependence on technology. Two studies done on teens with “Internet Addiction Disorder” both showed significant atrophy of interbrain connective pathways. (Lin et al 2012, Aubusson 2013) Another study done on “Online Gaming Addicts” also showed significant white and gray matter atrophy in several regions of the brain including portions of the frontal cortex. (Weng et al, 2013) And yet another study done on internet addicted teenage boys showed they had a significant decrease in the cortical thickness of their cerebral cortex. This would seem to indicate a decline of neurons in this region and would lead to diminished cognitive abilities. (Yuan, 2013)

The mystery of our disappearing brain and brain function starts to become clearer as neuroscientists start to make sense of these three pound lumps of gray and white matter lodged uncomfortably into our disproportionately large heads. With recent advances in technology, (MRIs in particular) our understanding of the workings of the brain has greatly improved over the last several decades. The information this technology has uncovered may ironically illustrate the problems technology in general creates for our brains.

Neuroscientists and psychologists are starting to discover the ability to problem-solve (or lack of ability) may come from how the child uses their brain in their formative teen years. The ability to look at brain function in real time that MRIs provide has shown the development of the brain is a much longer and more involved process then initially thought.

From infancy until the age of two, a child’s brain begins the process of hardwiring itself. The 10 billion neurons start forming nearly 100 trillion connections to all of the different motor and sensory inputs of the body through a series of connections known as synapses. These series of nerves and synapses act as two way bridges that relay information (through what is known as a neurotransmitter) from a body part like the eyes, to the optic portion of a person’s brain. The brain instantly deciphers the information and sends a message back to the eyes telling them what to do next. All of this happens almost instantaneously. (Weinberger, 2005)

There are over 80 billion of these nerves connecting virtually every body part and organ to your brain and even interconnects different regions of the brain. There is not just one pathway connecting a single input to a single output. As the brain develops in an infant, it is unsure of what type of mental stimuli it will encounter or what it will be expected to do with it. So to play it safe, the brain overcompensates by allowing pathways to connect virtually everything in the brain and body to everything else. This allows the brain to develop in a seemingly infinite number of possibilities in which it is tailored to perfectly fit its environment. It is this interconnectedness of the different regions of the brain that gives people their intelligence. (Sherwood, 2014)

Here is where the problem lies. The brain starts off with too many of these synapses and pathways. It simply does not need them all. These pathways use energy to stay open. Going back to the concept of evolving for 200,000 years in a calorie scarce environment, the brain is a very efficient machine and it hates to waste energy. So from the age of two to five, a toddler’s brain starts realizing what pathways his or her brain is actually going to need, and what pathways it does not. If the brain rarely uses a particular pathway, it simply closes it down and discards it. This is an important developmental process known as “pruning.” Just a gardener would cut back the branches of a bush or tree that has become overgrown, the brain removes underused synapses to strengthen the synapses it does use. If the brain did not do this, the excessive amount of synapses would be too much for the brain to handle, and would be unable to focus on the pathways it actually needs. (Weinberger, 2005)

This creates the “use it or lose it” principle of cognitive ability. If a toddler has never connected a particular sensory input to another output or the brain hasn’t made the connection between different cognitive abilities, it will literally remove that particular synapsis in order to strengthen the ones it does use. For example, if a toddler has never heard a particular sound by the time the vocal synapsis prune, it becomes virtually impossible for the child (and subsequently, the adult) to mimic that sound. This is why it becomes almost impossible for native born English speakers to pronounce many of the completely unique sounds of East Asian languages, and vice versa. If the child has never heard a particular sound and attempted to mimic it at the end of the language acquisition faze of their cognitive development, the synapsis in the brain that would make pronunciation of these words possible will be removed so the brain can focus on pronouncing the sounds it has encountered. This is why it is much easier to acquire a language at a young age before the brain has been hardwired rather than as an adult. This is not just the case for language acquisition but true for all aspects of brain function.

The importance of pruning in toddlers has been known for some time. However more recent discoveries have shown that teens age twelve to eighteen also go through a significant period of growth and pruning in the prefrontal cortex. Despite the fact that the brain is roughly 95% of its adult size by the age of six, the prefrontal cortex goes through an increase in density of gray matter as it continues to hardwire itself during a later growth spurt. (Weinberger, 2005)

This late stage pruning makes the teenage years vitally important to the development of higher level cognitive skills. Dr. Jay Giedd, a neuroscientist at the National Institute of Mental Health in Bethesda, describes “[i]f a teen is doing music or sports or academics, those are the cells and connections that will be hardwired. If they’re lying on the couch or playing video games or MTV, those are the cells and connections that are going to survive.” (Weinberger, 2005)

It also means that if a teen underutilizes the portions of the prefrontal cortex used to solve problems, the brain will view this portion as unnecessary and begin the process of removing the synapses connecting it to other regions of the brain.

How is it possible the human brain could view the problem solving regions as unnecessary? Rarely today do teens come across a question or a problem that cannot be instantly answered or solved by a Google search. If a student is facing a challenging critical thinking question, all they need to do is type it into a search engine, and they will come across a variety of sources most likely with the answer provided for them. This is an example of the plasticity and adaptability of the brain, which has been our greatest strength from an evolutionary perspective, becoming a weakness.

  • Adler, J. (2013, June 1). Why Fire Makes Us Human Cooking May Be More than Just a Part of Your Daily Routine, It May Be What Made Your Brain as Powerful as It Is. Smithsonian Magazine June 2013.
  • Aubusson, K. (2013, March 6). Internet addiction affects brain. Psychiatry Updatel
  • Haviland, W., Walrath, D., Prins, H., & McBride, B. (2011). Evolution & prehistory: The human challenge ( ed., pp. 193-195). Belmont, CA: Wadsworth/Cengage.
  • Lin, F., Zhou, Y., Du, Y., Qin, L., Zhao, Z., & Xu, J. (2012). Abnormal White Matter Integrity in Adolescents with Internet Addiction Disorder: A Tract-Based Spatial Statistics Study. PLOS ONE, 7(1). Retrieved December 15, 2015, from
  • McAuliffe, K. (2011, January 20). If Modern Humans Are So Smart, Why Are Our Brains Shrinking? Discover Magazine.
  • Pearce, E., Stringer, C., & Dunbar, R. (2013). New insights into differences in brain organization between Neanderthals and anatomically modern humans. Proceedings of the Royal Society B: Biological Sciences, 20130168-20130168. Retrieved December 15, 2014, from
  • Sherwood, C., Subiaul, F., & Zawidzki, T. (2008). A Natural History Of The Human Mind: Tracing Evolutionary Changes In Brain And Cognition. Journal of Anatomy, 212, 426-454.
  • Weinberger, D. R., Elvevag, B., & Giedd, J. N. (2005). The adolescent brain: a work in progress.
  • Yuan, K., Cheng, P., Dong, T., Bi, Y., Xing, L., Yu, D., … & Tian, J. (2013). Cortical thickness abnormalities in late adolescence with online gaming addiction. PloS one8(1), e53055.

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