Diet influences jaw shape

Jaw shaping

It's not your genetics. It's your diet that's making your teeth crooked.
An article in the Proceedings of the National Academy of Science concluded that diet during growth determines the shape of the mandible, or the lower jaw. Eating softer foods causes the mandible to be shorter and smaller, which gives less room for the same number of teeth, resulting in tooth crowding.

What most people don't realise is that bone shape is determined by the forces acting on it, and not by a predetermined pattern. There is a basic pattern set down in genetics, but the specific and complex shape of our bones is created by muscles pulling on bones and gravity pulling down on our skeleton. Bone is an active tissue, and the bone will reshape itself if the forces acting on it change. Because of the mineral scaffolding of the bone, these changes take place over a prolonged period of time, and so may not be completely obvious at first. Even so, these hard structure can reshape to become curved when once straight, or thickened when once narrow.

Chewing on tough and fibrous materials would have caused an increased in muscle mass around the jaw, and these muscles pulling more vigorously on the mandible would signal the mandible to become bigger and thicker in response. A wider mandible gives more room for teeth. The study found the result to be consistent across cultures. The cultural change that led to this physical change was a move from hunter/gatherer to farming and sedentary lifestyles.

I have a personal experience with this phenomenon of bone reshaping. My cat was brought to the emergency room as a stray kitten hit by car and had a broken pelvis (and broken sacrum and two fractured femoral heads). Animals usually recover well if they just rest for 6-8 weeks with pelvis fractures. My cat did very well and runs and climbs almost normally, although her pelvis looks a little tilted. Out of curiousity, I took recheck radiographs a year later. On the left hand side, my cat had created a second acetabulum cranial to the first! The acetabulum is where the femoral head sits in the pelvis; normal people and animals have one on each side, one for each femur. My cat has 3 - one on the right, normal, and 2 on the left - one that was created in utero and used for her first 4-5 months of life, and the second that was created after her left femoral head moved cranially during the trauma. Somehow the muscles around the hip joint mimicked that of the original hip joint, and in response, the pelvis created a bony lip around the femoral head to stabilise it, and voila! a new acetabulum. It's amazing how the body can respond to trauma.