All problems are a mix of genes and the environment. The genetic influence on facial development is obvious and environmental things such as thumb sucking has long been recognised. It is not often appreciated how influential the environment is and what a dramatic effect on facial shape changing this can make.
Interestingly all our ancestors had perfectly straight teeth, as all the other 5,400 species of mammals except some domesticated cats and dogs, some feral foxes (in Europe) and zoo animals. Over the last 10,000 years, while our genes have not changed at all; whenever, and wherever our ancestors became civilised they developed crooked teeth (malocclusion).The irregularity has been in proportion to the level of civilisation with the last hundred years have seeing a dramatic rise in the levels of malocclusion.
The environment has a great influence over the tooth positions and shape of the face shape.
1) It is universally accepted within dentistry that the teeth and bone occupy a space between the soft tissues of the tongue and the lips and cheek. In an ideal swallow, the lips and cheek should be completely passive. The problem appears to be that individuals never fully convert from an infantile suckle to an adult swallow. The change from breast to baby feeding has long been suggested to be the cause of this,but lacked evidence. A more contemporary view is that by feeding infants very soft food that they can physically suckle before they have gained the reflex to swallow, encourages them to adapt the suckle with their tongue between the teeth and never fully convert.
Anyone whose facial muscles can be seen to move when they swallow are not in balance, sometime the teeth resist these forces but usually they are affected. The face should be completely passive during swallowing.
2) A change from a very hard diet that was very low in calories to a very soft diet that is exceptionally calorie dense, just at the time that far less calories are needed. It is estimated that while we are using our bodies about 30% as much as our ancestors
we are using our jaws some 3% as much, and as every astronaut returning to earth knows, you use it or lose it. For example muscular dystrophyand muscle wasting diseases, such as Stephen Hawkins has (pictured), who grew normally before the onset of the disease that has dramatically changed the shape of this face.
3) Change in the oral and body posture. Nearly all children experience at least one blocked nose in early infancy, most have complete nasal blockage for days at a time, when they are forced to lower their tongue and open their mouths to breath. This becomes a habit during the very period that they are learning to walk and program their postural centres. This picture shows the effect of this on a child who was almost fully grown but developed a blocked nose causing his face to grow down, the effect on younger developing children is even greater.
By changing the environment it is possible to change the direction of growth and the more horizontal the growth then the more space there is for the tongue to move up out of the airway to allow a normal head , neck and tongue function, and allowing the teeth to align naturally without mechanical intervention.
Most people are unaware that the orthodontic profession openly admits that it does not know the causes of malocclusion, except for less than 5%, which are the cases of syndromes, diseases, infections and trauma. For the everyday normal health child the profession has no idea what the cause of the problem is.