It's not merely genetics. Environment plays more of a key role.
I agree. It's a confluence of factors. We can't forget that breastfeeding is a factor in early jaw development. Back home, only 1 in 3 children are exclusively breastfed for six months. I highly doubt they engage in long-term breastfeeding of 1-2 years. Add to that a rise in processed food, poor oral habits and mouth breathing, and there you go.
what? Back home i would say 3 of 3 suckle their moms until complete