Modern humans are the worst-breathing species on the planet

Nestor opens with a provocative claim, drawn from research into ancient skulls and modern jaw studies: humans today have smaller mouths, more crowded teeth, and narrower airways than our ancestors did, and even than many other mammals do, largely as a byproduct of softer, processed modern diets that don't demand the vigorous chewing that once helped develop wide jaws and open airways in childhood.

He visits an orthodontist, along with researchers examining preserved skulls across centuries, and finds a consistent pattern: as diets industrialized, jaws narrowed, airways constricted, and problems like crooked teeth, snoring, and sleep apnea — nearly nonexistent in some historical and hunter-gatherer populations — became widespread.

The consequence isn't cosmetic. A narrower airway makes nasal breathing physically harder, pushing people toward mouth breathing, which Nestor argues sets off a cascade of downstream health effects covered throughout the rest of the book.

Takeaway: many modern breathing problems trace back to structural changes in jaws and airways caused by softer diets over generations.