A book about the genetic evolution on the jaw from a award winning Stanford scientist and author of over 50 books. The evolution of modern speech, instead of just grunts, led to an important change in human anatomy. The top of the larynx leading to our lungs dropped, making a larger air space above it and behind the tongue that can be used to greatly modify the sounds our exhaling air can make. This has huge advantages, but like many evolutionary advantages it carries disadvantages as well. Thus the advantages of walking on our hind legs is paid for in back pain and hernias, while those of being able to speak are paid for with a higher probability of choking to death since air and food travel the same pipe in the neck. Infants are spared this threat since the dropping of the larynx doesn't occur until about 2 years old, allowing infants to suck and breathe simultaneously. The agricultural revolution had another impact. For hundreds of millennia human women breast fed their children for years, eventually weaning them on the tough, chewy foods they themselves ate.

Human developmental systems evolved so that the results of this regime were a healthy pattern of skull and jaw development. But with the evolution of agriculture these patterns began to change. Softer foods for weaning became available. Thus one result of the agricultural revolution has been an upsurge in serious oral problems, related to the soft foods onto which young infants in agricultural societies are usually weaned. Early weaning may lead to distorted patterns of muscle use that change the basic patterns of oral development. The effects can easily be seen by comparing the facial structures of rich and poor people from a few centuries ago. The jaws of the rich tend to be underdeveloped, palates narrowed, and the airways more compressed. Ehrlich and Kahn argue that education is urgently needed, not only within the medical and dental communities, but also among the broader public.

They have thus written an engaging book that outlines the basic history of the problems, comparing different societal norms around the world to support their arguments. They do not present a "fix", but instead argue that some simple changes to infant dietary recommendations and childhood nutrition can have significant adult benefits.