When humans turned from hunting and gathering to farming approximately 10,100 years ago, they set our species on a road of genetic variation that led from longer, sturdier mandibular structures to shorter jaws better suited to chewing softer food. As a result, tooth overcrowding-and orthodontia-are now one of the hallmarks of civilization.
According to a study done by researcher Noreen von Cramon-Taubadel, PhD, an anthropologist a the University of Kent in UK, global variations in jaw structure, in contrast to skull shape and facial features, are not attributable solely to genetic shift, but to a limited kind of natural selection. He looked at skull and jaw shape in 11 populations, six of which live by farming and five of which are hunter-gatherers. The populations included people from Africa, Asia, Australia, Europe, and the Americas.
von Cramon-Taubadel concluded that the transition to farming-and easier-to-chew food led to smaller, less-robust jaw structures and , according to the study abstract, "to increased prevalence of dental crowding and malocclusions in modern postindustrial populations."
Journal of the California Dental Association, March 2012.