The most important job of the brain is to ensure our survival, even under the most miserable conditions. Everything else is secondary. In order to do that, brains need to: (1) generate internal signals that register what our bodies need, such as food, rest, protection, sex, and shelter; (2) create a map of the world to point us where to go to satisfy those needs; (3) generate the necessary energy and actions to get us there; (4) warn us of dangers and opportunities along the way; and (5) adjust our actions based on the requirements of the moment. And since we human beings are mammals, creatures that can only survive and thrive in groups, all of these imperatives require coordination and collaboration.”

— Bessel van der Kolk, The Body Keeps the Score: Brain, Mind, and Body in the Healing of Trauma