Braces, rubber bands, even jaw surgery\u2014millions endure them in pursuit of a straighter smile. But were misaligned smiles always this common? Research suggests that might not be the case.<\/p>\n
While malocclusions\u2014crowded or misaligned teeth\u2014have been found among our hunter-gatherer ancestors, they appear to be more prevalent in modern populations. So what changed? Experts say the answer isn\u2019t simple but point to one possible culprit: our diets. As we traded raw, tough foods for softer, more processed ones, the burden of chewing decreased, allowing our jaws to shrink over time.<\/p>\n
Now, researchers are exploring how evolutionary biology, diet, and modern lifestyles may have reshaped our faces\u2014and our smiles.<\/p>\n
How farming may have reshaped the human face<\/p>\n
Ancient human skulls were strikingly different from our own. Early hunter-gatherers had large, powerful jaws<\/a> built for the demanding work of chewing tough meats, fibrous vegetables, seeds, and nuts. But around 12,000 years ago, things began to change. As humans around the world traded hunting for farming, their diets changed too, incorporating more grains and cultivated produce into their diet.<\/p>\n These foods were softer, more processed, and required far less chewing.\u201d We did not have ice cream or white bread back in the day,\u201d says Sue Herring<\/a>, professor emeritus in orthodontics at the University of Washington. \u201cWhen you get your food straight from the environment, it\u2019s probably a little [grittier] than stuff which has been cooked and processed.\u201d<\/p>\n (Neanderthal teeth reveal intimate details of daily life<\/a>.)<\/p>\n With softer diets came less mechanical strain<\/a> on the jaw. Over generations, our mandibles began to shrink\u2014 a trend visible in the fossil record<\/a>. That shrinkage is, at least in part, adaptive and the result of millennia of evolution, says Myra Laird<\/a>, assistant professor of basic and translational sciences at the University of Pennsylvania School of Dental Medicine. \u201cIf you don\u2019t need a huge mandible, it\u2019s energetically costly to build that extra bone.\u201d<\/p>\n But not all changes in jaw size and shape are evolutionary. Bone is highly responsive to physical stress\u2014even within a single lifetime\u2014and builds up around muscle attachment sites. In other words, less muscle usage results in less robust bones, Laird says, citing studies of craniofacial growth in non-human animals like hyraxes<\/a>. \u201cIf you switch to a liquid diet, you will not use your muscles as much and see some shape changes in your face.\u201d<\/p>\n (Here\u2019s how ultra-processed food harms the body and brain<\/a>.)<\/p>\n That\u2019s exactly what researchers believe happened to humans as they adopted agriculture<\/a>. \u201cPost-agricultural populations had a marked reduction in the size of the chewing muscles,\u201d Laird says. \u201cWhat this suggests is that the origins of agriculture brought about less work for the feeding system\u201d\u2014and, ultimately, much less roomy mouths.<\/p>\n How smaller jaws may be crowding our teeth<\/p>\n So, what happens when you try to fit the same number of teeth into a smaller jaw space? Over-crowding and crookedness.<\/p>\n \u201cThe way your teeth come through is almost like a zipper,\u201d says Julie Lawrence<\/a>, assistant professor of biological anthropology at the University of Nevada, Las Vegas. \u201cYour jaw moves forward and then it makes space for them to come through.\u201d If there isn\u2019t enough room for the teeth to erupt, they might become impacted or crowded together. The third molars, or wisdom teeth, are particularly at risk for noneruption in undersized jaws. Research suggests<\/a> that the mismatch between the size of the mandible and dentition may be to blame for increasingly crooked teeth among post-industrial humans.<\/p>\n \u201cThat loss of space is really what precipitates the malocclusions, dental crowding,\u201d says Laird. \u201cThe rate of malocclusion goes way, way up [in modern humans], and that is ubiquitous across all populations.\u201d<\/p>\n (Why we add fluoride to water\u2014and how it became so controversial<\/a>.)<\/p>\n