Mouth breathing is one major culprit.
Agree with genetics ..... and the mouth breathing causes lower jaw to grow down, instead of forward.
Bone structure from relatives ... My dad is very narrow (especially upper) my mum is wide with big teeth. I got narrow, dad(especially upper) with big teeth from mum. The mouth breathing then caused the severity of lower jaw growth issue.
Now my son has it, but my daughter looks even jawed at this point! My son also breaths through his mouth and daughter doesn't.
I think that is a poor way of looking at it. I've done years of research and have a bit of understanding of medicine and science. I do think it is fully environmental. Think of it!
We breed dogs together, two different breeds with two very different facial and body aesthetics. We have really seen no issue with dogs with too big teeth vs that of the muzzle. Those genetics work together regardless of the different breeds. It really does come down to the environment; food, hormones, family habits...etc.
Our society (I mean 1st world) that relies on impure food sources or excess salts and sugars have been the cause of a shift that has steadily been happening faster with industry.
There are several things I have found
A)narrowness of our jaw, stems from a softer food pallet (cooked, so we don't have to chew) or sugars/simple carbs, aka the western diet.
Less chewing results in less muscle build up of our facial muscles, which means we have weaker jaws. Weaker jaws can lead to mouth breathing while asleep or even while awake.
(This cooked diet also in turns removes important nutrients which we would benefit more from. )
Which in turn can lead to vertical maxillary excess.
B) i. More people in a conjested place means more sickness, allergies, and pollution which leads to stuffy noses.
Stuffy noses leads to compensation by mouth breathing
ii. Mouth breathing also has several health factors besides dehydration which can cause a doughy skin tone, large dark circles of around the eyes, it does more then reform growing bone.
C) With bone growth growing vertically, this also plays different factors and stresses on muscles of the face, and fat deposits which I know some people on here mentioned.
I am not convinced, I think we can take a look at European faces before and after industrialization and find that is the culprit.
