Consider the human brain: Somehow, its several billion invisible cells serve to produce emotions, thoughts, and dreams. The deeply wrinkled surface of the brain's identical halves contains the substance that makes a mind, able to soar on the notes of a bird or the colors of a sunrise, suffer the deepest anguish from pain or loss, or simply be bored. Millions of tiny changes in molecular currents within the brain, each instant, create all of these emotions, and can lead a person to seek the source of all things in the universe.

Nerve cells in the cerebral cortex have many nerve fibers branching from them. These fibers provide thousands of possibilities for different connections to be made in the brain, and facilitate rational thought, planning, and problem solving.

While humans, the great apes, and perhaps the whales, dolphins, and elephants, have the most complicated brains, all...