Three-Brains-in-One Brain

(updated 08/2016)

  • Brain One: Housekeeping

  • Brain Two:          Emotion

  • Brain 3:              Thinking

You may have thought all you had was one, but inside there are two more brains.


you already

knew this from

your experience:

for example, remember

a time when you really wanted

to do something, but you felt you shouldn’t?

The most illogical or irrational “wants” we have probably derive from older parts of our brain,

while the understanding of smart versus dumb

choices comes from the newest part.

If that idea offends you,

or seems just too




you might take a

“de-tour” for a moment

and read an essay on science.

Take another example:

you can be hungry,

but not feel it

until you

pay attention to it;

then when you do notice,

you realize you’ve never been

hungrier than this for a very long time.

Hunger comes from the most basic parts of our brain,

but our awareness of it is controlled by the newest part. Here are the 3 brains:

Brain One: housekeeping

This is the brain we share with owls, and lizards. Think of it as the “housekeeping brain”. Just the basics: hunger, temperature control, fight-or-flight fear responses, defending territory, keeping safe — that kind of stuff. The structures that perform these functions within our brain are extremely similar to those in the brains of reptiles. Thus, this brain is called the “Reptillian Brain”.  You can take use this brain when you wish; and you will see parts of it when you are obsessed with something.


Brain Two: emotion

As animals became more complex, other structures were added around the Reptillian Brain in a shell, or “girdle”. The Latin for arc or girdle is “limbus”, and this brain is called the limbic system. We humans share this brain with older mammals like dogs, cats, and horses, and mice (as opposed to newer mammals like chimps; we’ll get to them in a moment). Their brains, and this part of our brains, are extremely similar.

Think about the difference between a mouse and a lizard, or between a whale and a snake, and you’ll recognize what this mammalian brain adds to a creature’s capacities. Mammals have “feelings” like ours. Everyone's limbic system is well clever at doing mood, memory, and hormones. 




 Brain Three: thinking (and much more)


Here is the familiar “cortex” you can see from the outside. With this brain, primates can do things that horses and cows cannot, like complex social interactions and advance planning (like planning a party for a neighbouring troop). In humans the cortex has grown to a huge size in association with our discovery of "language". Other primates like chimpanzees, or monkeys, have much less cortex, which is surprising since chimpanzee DNA differs from ours by only 1.6%! (stunning, really; I hope you are stunned. Recently some technical issues have arisen with that percentage, but for the time being it’s generally regarded as, well, mind boggling!). If you wonder why we humans have populated the entire globe, while our chimp relatives are stuck in a shrinking rain forest with their nearly identical DNA.  You’ve got a great question, and Monoganon has a great answer...