See my comment below, and the book "Breath" by Nestor: https://news.ycombinator.com/item?id=24247066 https://news.ycombinator.com/item?id=24247066 And this on

See my comment below, and the book "Breath" by Nestor: https://news.ycombinator.com/item?id=24247066 https://news.ycombinator.com/item?id=24247066 And this one about the book "Jaws" by Kahn: https://news.ycombinator.com/item?id=23435964 https://news.ycombinator.com/item?id=23435964 The short answer is that two big changes in human history led to this problem: 1. Agriculture. Our diets drastically changed when we started growing food, and that had enormous impact on our jaw, breathing, and facial structure. If you've read Jared Diamond (Guns, Germs and Steel) or more recently Sapiens, you'll understand this. They describe agriculture as an advance for the human race, but a setback for individual humans! 2. The industrial revolution. There was a huge population explosion, and we fed all those mouths with even more monotonous diets (more bread, rice, corn, factory farms, etc.) This is taking agriculture to the next level. We replaced animal power with machines in many cases. ----- If you want a visual, the book "Jaws" tells about Europeans who came to the Americas in ~1600. The Europeans had the benefits of technology that let them travel across the sea, but were closer to 5 feet tall, and they had terrible teeth, and malnutrition. There was a dentist by the name of Price who observed the Native Americans. Basically he was like "WOW they are 6 feet tall and they have beautiful jaws! They breathe through their nose and not their mouth. They don't sleep with their mouths wide open, and they don't snore." Mouth breathing is a sign of poor breathing. Just like a boxer knows to breathe through his nose, but when he gets hit too much and tired, he starts breathing through his mouth. When you're sleeping, you're supposed to breathe through your nose as well (because the organ is made for it), but many people breathe through their mouths due to having obstructed airways. Which are result of diet, weight, and lifestyle.