Soft foods cause crooked teeth. Ancestral humans ate raw tubers and other very chewy things that exercised their jaws, and the growing human body needs this resistance/exercise. If you look at modern hunter-gatherer tribes with traditional diets, they have a far lower rate of crooked teeth we'd solve with braces than the developed world.

Sterile environments/too-low pathogenic load causes allergies. The immune system expects a base-rate of infection; if it doesn't see that, it upregulates. Allergies are a first-world disease; they're far less prevalent in less developed countries, and you even see the effect in immigrants- their allergy rates go up after a few years of living in a developed country.

> Or do you seriously believe all prehistoric humans had 20/20 eyesight?

The prehistoric realities were harsh and nearsighted individuals had little chances of survival and procreation (natural selection). In the modern society perfect eye-sight is not as important for survival as in the prehistoric society, thus more tolerance to its greater variability.

Sunlight exposure has been shown to be protective of eyesight, and we spend more time indoors focusing on screens.

The timespan is too short for evolution to have had a considerable impact.

> The timespan is too short for evolution to have had a considerable impact.

I am not talking about evolution as in developing new species but about survivability of naturally occurring variations. Modern humanity timespan is not enough in developing new genetic traits but long enough to alter effects of natural selection. BTW, due to advances in medicine nowadays we have children born and survive into adulthood with medical conditions that were terminal just 100 years ago. Survival variability (in developed world) is much broader that it was in recent historic past (e.g. middle-ages). This is a plain fact.

But the timeline is too short even for that. The number of children who survive today, despite genetic issues, who would not have survived 100 years ago, is miniscule compared to the extent of nearsightedness today.