What Our Jaws Were Made For
Our ancestors had to grind down foods for hours each day. Foods from thousands or even hundreds of years ago were completely different to what we see in grocery stores today as they were less processed and very hard to break down. This meant that your jaw had to work hard for every nutrient, resulting in stronger jaw muscles and developed facial structures without crooked teeth. Looking at the skulls of our ancestors this is evident. And wild animals always have perfectly aligned teeth. Crooked teeth is something that didn't exist before and only occurs with modern human beings.
Read more about the reasoning behind the movement to stop bad facial posture and soft diets.