I have discussions frequently with people who swear that humans were vegetarians and meat eating is a relatively new thing. If that were the case we'd have much smaller jaws by now. According to the article below, teeth crowding is a by product of eating more grains.
How Agriculture Made Our Mouths Too Small for our TeethThe rise of agriculture allowed for the development of complex societies and technologies that likely wouldn't have been possible otherwise. It also wreaked havoc on human health. And we can add a new downside to the list: our misshapen mouths.
That's the finding of University of Kent researcher Noreen von Cramon-Taubadel, who examined 295 human jaws from various museum specimens around the world. She found that, even adjusting for climate, geographic, and genetic variation, a consistent pattern emerged: people from agricultural societies have significantly smaller mouths that their counterparts in hunter-gatherer societies.
In itself, that wouldn't be such a bad thing, but the problem is that we all have exactly the same number of teeth. Von Cramon-Taubadel speculates that agricultural societies tend to produce people with smaller jaws because the ground grains and processed animal products we eat are softer than the wild plants and animals eaten by hunter-gatherers. In animal experiments, subjects fed a softer food diet developed smaller jaws than those fed tougher foods. This could well explain why dental crowding is so widespread, and why so many people end up needing to wear braces.
This isn't really a case of evolution or selection - instead, it's that generations of agricultural humans have all tended to develop similar, smaller jaws because they were all raised on the same soft diets. This would be the first clear instance in which widespread anatomical differences in humans on this sort of scale are the result of lifestyle factors, as opposed to simple genetic variation. To be sure, this doesn't represent a definitively proven link, but anyone who has ever worn braces is well within their rights to feel angry with the whole concept of agriculture right now.