Illustration and theory from The Triune Brain In Evolution (Plenum Press, 1990)

by Dr Paul MacLean, head of Brain Evolution and Behavior department of the (U.S.) National Institute of Mental Health.

The Paleomammalian Brain (also known as the Limbic System).

This brain began evolving about two hundred and twenty million years ago. It was built around the older Reptilian Brain.

The Neomammalian Brain (also known as the Neocortex).

This brain began evolving about 500,000 years ago. In humans, it has grown extraordinarily fast, encompassing the more ancient brains.

The Reptilian Brain (also known as the R-Complex or the Basal Ganglia).

This brain evolved in vertebrates well over three hundred million years ago.

This, my friends, is the apparatus we all carry around in our skulls---

the human brain.

It is, as you can see, not a single brain, but actually three brains in one. As we endeavor to "know who I am," it seems appropriate to not only search our psyches and our sciences and our religions, but to search the fundamental physical mechanisms within our heads.

I think you may have a major surprise in store for you.

To get a brief and general description of each brain, click on the names of each brain above. But first peruse the quote from Dr MacLean below.

........"The human brain evolves and expands along the lines of three basic patterns characterized as reptilian, paleomammalian, and neomammalian.

"Thus the relevance of work on animals to human affairs becomes apparent. Figure (above) suggests how the three evolutionary formations built on one another --- Radically different in chemistry and structure, and in an evolutionary sense countless generations apart, we have, so to speak, a hierarchy of three-brains-in-one, or what may be appropriately referred to as a triune brain.

"What this situation implies is that we are obliged to look at ourselves and the world through the eyes of three quite different mentalities. To complicate things further, there is evidence that the neural machinery underlying the two older mentalities lacks the capacity for verbal communication. But to say that they lack the power of speech does not belittle their intelligence, nor does it relegate them to the realm of the unconscious.

"Stated in present-day terms, one might imagine that our brain represents an amalgamation of three biological computers, each with its own special intelligence, subjective sense, sense of time and space, memory, motor, and other functions. What seems notably lacking is a neural code for inter-signaling in verbal terms.

"... I should point out that the basic neural machinery required for self-preservation and the preservation of the species is built into the lower brain stem and spinal cord. This neural chassis might be compared to the chassis of an automobile or other vehicle requiring a driver.

"The odd situation that we must consider is the evolution of three different drivers for the same vehicle, all of different minds, and all located in the forebrain above the neural chassis.".........