Our human brain contains the foundations of vertebrate brain evolution: our reptilian brain (our Lizard Legacy) and our paleo-mammal brain (our Furry L'il Mammal). Evolved later is our human rational brain, the neocortex (our Monkey Mind), and highly developed in the human are the prefrontal cortex or frontal lobes (our Higher Porpoise; higher purpose).
This fascinates me, because most folk think about the Mind as if its just one holistic entity. But in fact, its evolution is based on four distinct regions.
Its also interesting when you relate these distinct parts to human suffering, like anxiety disorders which seem to manifest due to dysfunction which arises between these different parts of the brain.
The sub-cortical or reptilian brain seems to be responsible for 1st fear or startle response. A very important survival instinct. Whilst secondary fear seems to emanate from our pre-frontal cortex as a interpretation of physical sensations derived from 1st fear. When this occurs the pre-frontal cortex keeps communicating to the sub-cortical region that its own response to a threat is a threat... creating a positive feedback loop between the cortical and sub-cortical parts. Which is obviously completely dysfunctional behaviour.