“The human brain bears the stamp of 400 million years of trial and error, traceable by fossils and molecular homology in nearly unbroken sequence from fish to amphibian to reptile to primitive mammal to our immediate primate forerunners.
“In the final step, the brain was catapulted to a radically new level, equipped for language and culture. Because of its ancient pedigree, however, it could not be planted like a new computer into an empty cranial space. The old brain had been assembled there as a vehicle of instinct, and remained vital from one heartbeat to the next as new parts were added.
“The new brain had to be jury-rigged in steps within and around the old brain, otherwise the organism could not have survived generation by generation. The result was human nature: genius animated with animal craftiness and emotion, combining the passion of politics and art with rationality, to create a new instrument of survival.
“Brain scientists have vindicated the evolutionary view of mind. They have established that passion is inseverably linked to reason. Emotion is not just a perturbation of reason, but a vital part of it. This chimeric quality of the mind is what makes it so elusive.
“The hardest task of brain scientists is to explain the products tested engineering of the cortical circuits against the background of the species’ deep history.” —E.O. Wilson, Consilience: The Unity of Knowledge