You may have thought all you
had was one, but inside there are two more brains.
Actually, you already know this from your experience: for example,
remember a time when you really wanted to do something, but you knew 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 "Western" or "scientific", you might take a
"de-tour" for a moment and read this 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 been
getting hungrier for a 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":
Center of the Brain
"limbic system" or
"old mammalian brain"
(Wrapped around Brain Two!)
This is the brain we share
with birds, and reptiles. 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 thing. 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 "R
complex" (R for reptilian). You can take a Tour of the R complex when
you wish; and you will see parts of it in the section on obsessions.
As animals became more complex, other structures were added around the R
complex in a shell, or "girdle". The Latin word
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 even 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
Think about the difference
between a mouse and a lizard, or between a cat and a snake, and you'll
recognize what this mammalian brain adds to a creature's capacities.
Mammals have "feelings" like ours. We'll be looking at the structures of
the limbic system in the sections on mood, memory, and hormone control.
The main parts of the limbic
system (except the thalamus, which is generally regarded as part of
Brain One) are shown below. By taking all the Brain Tours you'll see
each of these parts and get a better sense of how this set of structures
is positioned underneath the cortex.
Here is the familiar "cortex" you can see from the outside. With this
brain, primates can do things that horses and cows
like complex social interactions and advance planning (such as planning
an attack on a neighboring troop). In humans the cortex has grown to a
huge size, somehow in association with our development 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're stunned.
Recently some technical
issues have arisen with this number, but for now, it's still generally
regarded as, well, amazing!). 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 -- read The Third
Chimpanzee, by Jared Diamond. You've got a great question, and his is a
(Similarly, if you wonder
why white-skinned humans seem to have an unfair share of the resources
and money, his other masterpiece offers a solid explanation beside skin
color: Guns, Germs, and Steel).
Three Brains in
To keep all this straight, think of the following image (ok, it's a
little odd, but it seems to work; write if you have another one).
R brain is like a golf club. Let's make it a driver, one of those with a
big fat wooden head. Hold the club so that the head is at the top.
There's your R complex, with your spine sticking down toward the ground.
The R brain is just a big swelling at the top of a spinal cord, and
that's how it developed. Worms have little swellings, snakes have bigger
ones. OK so far?
Next we'll add the layer
that makes mammals behave so differently from reptiles. This next
"layer", the old mammalian brain, evolved on top of the R complex. It
was not a remodel so much as an addition, like adding on bedrooms all
the way around a kitchen/bathroom.
This addition covers the
entire R complex, leaving the R complex deep within the brain. In our
model, take the golf club, and cover the head with a sock; a big thick
red one would be nice. Now you have the R brain (golf club), with the
old mammalian brain wrapped around it (sock). Notice that the red sock
forms a shell, or continuous border around the golf club head.
To complete the brain picture, add a bicycle or hockey helmet on top of
your red-socked golf club head: that's the newest mammalian addition,
the "cortex", and it is the grey squiggly stuff you can see on the