I would say genetics had something to do with it. Different isolated pre-historic cultures over tens of thousands of years would each tend toward a degree of h

I would say genetics had something to do with it. Different isolated pre-historic cultures over tens of thousands of years would each tend toward a degree of homogeneity genetically, sometimes drastically different than other distant isolated cultures. Some of the diverse features would have to do with jaw size and tooth size, some lines ending up with much more sizable mouth parts than others. Crossing a small-jawed strain with one having much larger teeth would likely end up with some offspring where the full number of teeth just do not fit, or don't fit as straightly as prehistoric or early historic specimens. This incidence has bound to increase dramatically with exponential rises in transportation and migration. To where it is so noticeable now, more people are finally asking the above question.