I’ve had people tell me many times that the average person only uses 10% of their brain’s full capacity. Is this true? No, it’s nonsense. Quoting from a Biological Anthropology textbook of mine:
We have all heard the myth that we humans use only 10% of our brains. Indeed, it is apparent that not only have many people heard it but they believe it. Psychologist Barry Beyerstein (1999) has spent many years researching the origins of this mistaken idea. Although he cannot pinpoint its origins with precision, he has shown that it has been around for quite some time. One of the first groups that latched onto and spread the myth was the early self-improvement (“positive thinking”) industry. For example, a 1929 advertisement states that “scientists and psychologists tell us that we use only about TEN PERCENT of our brain power” and that by enrolling in the course being advertised, a person might tap some of that brain that is not being used. The advertisement uses the 10% figure as though it were common knowledge. This indicates that the origins of the myth must date to significantly earlier than 1929. Although Beyerstein has tried to identify the “scientists and psychologists” who may have said something like this, he has so far failed to find any specific reference to it in the literature.
Even if the 10% figure came from a scientist working at the turn of the twentieth century, the state of the art of neuroscience was not particularly advanced at that time. Most people would agree that any sweeping scientific pronouncement, based on little empirical research, is eventually due for some reconsideration. Indeed, there is plenty of evidence from neurology and psychology that the 10% figure is wholly untenable; it is basically neuro-nonsense.
One of the most compelling arguments against the 10% myth comes from the perspective of energy and evolution. The brain uses a lot of energy. In humans, it accounts for about 2% of the body mass but uses about 10-20% of the total energy and oxygen consumed by the body. It is an “expensive tissue” (Aiello and Wheeler, 1995). The brain cannot store significant energy reserves, and is extremely vulnerable if the oxygen supply is cut off.
From an evolutionary standpoint, maintaining such an expensive organ only to use 10% of it does not make any sense. When you consider that there are other costs associated with large brain size (such as birth difficulties; see Chapter 17), if we used only 10% of the brain, there would have been substantial fitness benefits in reducing the brain to a more efficient and less costly size. This did not happen, of course, as brain expansion has characterized evolution in genus Homo.
Leslie Aiello and Peter Wheeler point out that the brain is not the only expensive tissue in the body. The heart, kidney, liver, and gastrointestinal tract consume at least as much energy as the brain. Human bodies use energy at about the rate that would be expected of a mammal our size. Given that our brains are much larger than would be expected for a mammal our size, how do we maintain the expected energy consumption rate? Aiello and Wheeler argue that a tradeoff with one of the other expensive tissues has occurred. Specifically, at the same time as the brain has increased in size in human evolution, it appears that the stomach and intestines have decreased in size. These size reductions presumably have been accompanied by a reduction in energy use. The smaller gastrointestinal tract also indicates a reliance on higher-quality, easier-to-digest foods (such as meat).
The complex relationship between behavior, brain size, diet, and gut size is one of the most fascinating problems in the study of human evolution. Although it is tempting to see brain size and gut size as engaged in a neat tradeoff, the situation probably was a bit more complex than that. Nonetheless, Aiello and Wheeler make clear that we have to pay for what we have: a large, energy-hungry brain. And a brain that wastes 90% of its volume could never have evolved.