Humans used to have straighter teeth—what changed?

Yahoo

2 days ago

Braces, rubber bands, even jaw surgery—millions endure them in pursuit of a straighter smile. But were misaligned smiles always this common? Research suggests that might not be the case.
While malocclusions—crowded or misaligned teeth—have been found among our hunter-gatherer ancestors, they appear to be more prevalent in modern populations. So what changed? Experts say the answer isn't 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.
Now, researchers are exploring how evolutionary biology, diet, and modern lifestyles may have reshaped our faces—and our smiles.
Ancient human skulls were strikingly different from our own. Early hunter-gatherers had large, powerful jaws 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.
These foods were softer, more processed, and required far less chewing.' We did not have ice cream or white bread back in the day,' says Sue Herring, professor emeritus in orthodontics at the University of Washington. 'When you get your food straight from the environment, it's probably a little [grittier] than stuff which has been cooked and processed.'
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With softer diets came less mechanical strain on the jaw. Over generations, our mandibles began to shrink— a trend visible in the fossil record. That shrinkage is, at least in part, adaptive and the result of millennia of evolution, says Myra Laird, assistant professor of basic and translational sciences at the University of Pennsylvania School of Dental Medicine. 'If you don't need a huge mandible, it's energetically costly to build that extra bone.'
But not all changes in jaw size and shape are evolutionary. Bone is highly responsive to physical stress—even within a single lifetime—and 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. 'If you switch to a liquid diet, you will not use your muscles as much and see some shape changes in your face.'
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That's exactly what researchers believe happened to humans as they adopted agriculture. 'Post-agricultural populations had a marked reduction in the size of the chewing muscles,' Laird says. 'What this suggests is that the origins of agriculture brought about less work for the feeding system'—and, ultimately, much less roomy mouths.
So, what happens when you try to fit the same number of teeth into a smaller jaw space? Over-crowding and crookedness.
'The way your teeth come through is almost like a zipper,' says Julie Lawrence, assistant professor of biological anthropology at the University of Nevada, Las Vegas. 'Your jaw moves forward and then it makes space for them to come through.' If there isn't 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 that the mismatch between the size of the mandible and dentition may be to blame for increasingly crooked teeth among post-industrial humans.
'That loss of space is really what precipitates the malocclusions, dental crowding,' says Laird. 'The rate of malocclusion goes way, way up [in modern humans], and that is ubiquitous across all populations.'
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But experts caution that the story isn't so simple. Although the frequency of malocclusions seems to have increased among modern humans, dental impaction and crowding have been observed in early hominid skulls. The fossil record is limited and likely not fully representative, Lawrence says. 'Better teeth tend to be better preserved,' she says, adding that anthropological data doesn't take into account confounding factors like missing teeth.
While 'there does seem to be a pattern' of increased malocclusions among post-industrialization humans, Lawrence adds, not all changes in teeth alignment can be attributed to diet. Extreme under- or overbite, for example, is the result of population genetics and 'doesn't have to do with industrialization.'
Many other factors can cause crooked teeth, including environmental conditions or developmental anomalies. And some populations are more genetically predisposed to malocclusions.
Ultimately, the prevalence of crooked teeth may also be due in small part to aesthetic bias. 'Our modern society is a lot more sensitive to cosmetic problems,' Herring says. 'I think we're a lot more aware of malocclusions now than anybody was in the past.'