This idea is easy to challenge on evolutionary grounds: Why would we evolve an organ that is only used to 10% capacity?

As any decent text on human evolution will tell you, our heads and brains are disproportionatly large as compared to other animals. This is not without costs and design trade-offs. See the significant costs of the large human brain.

Due to these costs, we should conclude that the large brain must have had strong benefits in order to evolve to that size. Any unused capacity would have been eliminated a long time ago.

Quite simply, if we could have had smaller heads or brains, even slightly, even 1% never mind 90%, without sacrificing intelligence, we would have.

Most of the above nodes are pretty vague, so I thought I'd provide a more detailed refutation of this falsehood. As kamamer notes, not a single study supports this notion. There are, however, several facts that are mistakenly cited as "proof" of this assertion:

  • A minority of brain cells are neurons.
  • Most of the cells in your brain are glia, not neurons; estimates of the proportion of glia seem to vary widely, but range from sixty to ninety percent. As of this nanosecond, neuroscientists don't think that glia are directly involved in the transmission of information that underlies thought (but stay tuned--the field changes on a daily basis). This observation leads some people to conclude that we're only using the minority of cells that are neurons. This is false, because glial cells serve several important roles; they hold your brain together, provide the myelin that insulates our neurons and facilitates neurotransmission, and so on. Claiming that we're only using our neurons to think is like claiming that you're only using your computer and your chair to read E2. You're also using the building's foundation, its electrical and telephone wires and the conduits through which they run, the walls and ceiling that prevent the rain from coming in and destroying your computer, and so on. Moreover, you can't magically start using your glia to think--you can't use them for information transmission any more than you could send email on an I-beam.

  • Most activities involve only a small part of the brain.
  • This statement is actually a little imprecise. As I said above, many regions are specialized for particular functions, but every region still depends on inputs from other regions. For example, some studies show a small area of cortex dedicated to face recognition, but this region obviously couldn't do its job without the input that travels from your eyes to the optic nerve to lower-level cortical areas and so on.

    Anyway, different parts of the brain are specialized for different purposes, and you can't really use one part for a different purpose. As kamamer notes, some of those areas are specialized for vital functions like breathing and, as with the glia, you can't get rid of them or coopt them for another purpose. Also, as picked brain observes, other areas are specialized for other nonvital functions, and you can't consciously reassign these regions, either. It's like anatomy in general--you can't use your pancreas to create a writeup, nor can you use your pinkie to digest protein.

  • People can recover from substantial brain damage.
  • True, but they don't necessarily recover quickly or completely. Furthermore, I've never heard of anyone recovering after losing 90% of his or her brain. Some children with severe and intractable epilepsy undergo a hemispherectomy, which involves the removal of slightly less than 50% of the brain, but that's about the maximum and even these children are not necessarily perfectly healthy.

I first heard this fictionoid from a woman who came to my grammar school to tell us why we shouldn't use drugs. When she described how it felt to use drugs, she said that when tripping, we leave the ten percent of the brain we usually use and "enter the realm of the other ninety percent that we don't usually use and can access only, like, in dreams and meditation and stuff." At the time, this weird description simply made drugs seem more appealing; later on, I realized that she had simply dropped too much acid.

In short, if you think that you're only using ten percent of your brain, I'll be happy to take the other 90 percent off your hands for you!

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