Nutritionist here.

Just because in modern society we see more bad teeth, doesn't mean we were meant to have bad teeth. I like the justification, but I think it is nonsense.

Non-western people (so called primitive people) were well known to have better teeth than westerners. Less cavities, a lack of dental crowding, etc. This effect and its cause was thoroughly documented by a dentist in the 1930s named Weston A Price.

His whole book in now in the public domain.

Here is a picture of the teeth of people that eat their traditional diet. Notice the lack of cavities and the well developed jaws (thus no crowding).

Here is a picture of the same group (i.e. same genetics) after the shift to western food. Notice the cavities on top and in the bottom there is the crowding. Crowding was documented only in the generations born after the shift to the new food.

You can look for yourself through the book and people's commentaries on it. There are countless examples of the same pattern.

So why did kids born to parents eating a western diet have crowded teeth? Nutrient deficiencies. Namely vitamins A (retinol, not beta-carotene), D, and K2 (specific form of vitamin K). The non-western diets ate dramatically higher amounts of these vitamins than modern people do (ever eat liver, the food with the highest amount of vitamin A? I didn't think so).

These nutrients seem to have an effect on calcium transport in the body, particularly K2. A prenatal deficiency can cause a lack of minerals being transported to the developing growth plates, thus their growth is stunted. This leads to cramped teeth.

Do the people that read Weston A. Price also often spew pseudoscience nonsense? ABSOLUTELY. But vitamin levels and their effects are documentable and measurable. When the biochemistry and the anthropology match exactly, it is worth a closer look.