James Nestor explores how the evolution of the human face has led to a modern crisis of obstructed airwaysand chronic illness. By investigating historical skulls and participating in a Stanford experiment, the author demonstrates that mouthbreathing destroys health while nasal breathing and slow respiration can reverse many diseases. The text highlights how our ancestors’ hard diets promoted wider jaws and better breathing, contrasting this with the narrow faces caused by modern processed foods. Innovative "pulmonauts" and ancient yogic practices are presented as vital tools for hacking the nervous system and boosting longevity. Ultimately, the sources argue that the simple act of shutting your mouth and harnessing carbon dioxide can profoundly heal the body.