There are five principles that are explained by Tooby and Cosmides that can guide us in understanding this domain.

Principle 1:

“The brain is a physical system. It functions as a computer. Its circuits are designed to generate behavior that is appropriate to your environmental circumstances.”

The brain is understood as a physical system, and the analogy drawn here is with the computer. It functions as a computer does, and like the computer the brain has its own circuits. Here we recall that the mind is defined in Evolutionary Psychology as a set of information-processing machines. The brain has its circuits which are designed to generate a particular kind of behavior – behavior that is appropriate to our environmental circumstances.

The brain generates appropriate behavior, and as a physical system it is governed by certain laws and these laws are the laws of physics and chemistry.

What is appropriate behavior? It is behavior that is appropriate to one's environmental circumstances. The point here is that different organisms have different appropriate behavior(s) for the same environment. Tooby and Cosmides argue that while the appropriate behavior for a machine is decided by an engineer, the appropriate behaviors for particular species are decided by Natural Selection.