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All these ancient skulls have perfectly straight teeth, despite almost certainly never sporting braces.
这些古代头骨的牙齿都非常整齐，尽管几乎肯定从未戴过牙套，
And this isn't some strange sample.
而且这些样本并非个例。
According to the fossil record, ancient humans usually had straight teeth, complete with third molars—or wisdom teeth.
根据化石记录，古人类的牙齿通常比较整齐，包括第三臼齿，也就是智齿。
In fact, the dental dilemmas that fuel the demand for braces and wisdom teeth extractions today appear to be recent developments.
事实上，如今助长牙套和智齿拔除需求的牙科难题似乎是近代的发展，
So what happened?
到底发生了什么？
While it’s nearly impossible to know for sure, scientists have a hypothesis.
虽然几乎不可能确定，但科学家们提出一个假设。
A couple million years ago, the ancestors of modern humans lived a subsistence lifestyle.
大约数百万年前，现代人祖先的生活方式是自给自足，
Their teeth and jaws had to work hard to make the food they ate digestible.
其牙齿和颌骨必须努力工作，才能使所吃食物更容易消化。
Indeed, the surfaces of many of their teeth show extensive wear and flattening.
的确，他们许多牙齿表面显示出严重磨损和变平，
They also had larger jaws and teeth overall.
颌骨和牙齿整体上也更大。
At some point, they began using tools and fire to cook and prepare food, which helped break it down.
在某个时期，他们开始使用工具和火来烹饪和准备食物，这有助于分解食物。
A lot more time passed and, around 12,000 years ago, some humans started farming and domesticating animals and plants.
随着时间推移，大约 1.2 万年前，一些人类开始耕作和驯化动植物。
Over the course of several thousand years, it became more common for people to process and refine their food.
在几千年的时间里，人们加工和精制食物变得越来越普遍，
Milling technologies helped remove the tougher parts of grains, like the germ and bran from rice and wheat.
粉碎技术有助去除谷物中较坚硬部分，如大米和小麦中的胚芽和麸皮。
Fast forward to the industrial Revolution, and technological innovations dramatically accelerated these processes.
到了工业革命时期，技术创新极大地加快了这些过程。
In a relatively short time, many human mouths were relieved of a great deal of their grinding, crushing, and pulverizing duties.
在相对较短的时间内，许多人的嘴从大量的研磨、压碎和粉碎的任务中解脱出来。
And interestingly, it was around this time that tooth crookedness appears to have become more common.
而有趣的是，就在这个时候，牙齿的歪斜似乎变得更常见。
Examining fossils spanning millions of years of evolution, researchers have observed a gradual decrease in tooth and jaw size in humans and our ancestors.
研究人员通过研究跨越数百万年进化的化石，观察到人类及其祖先的牙齿和颌骨尺寸逐渐减小的趋势。
Many think that, for most of human history, dietary shifts— like the introduction of meat and the advent of cooking—were gradual, and that changes in tooth and jaw size basically kept pace with one another.
许多人认为，人类历史的大部分时间里，膳食变化，如肉类的引入和烹饪的出现，是逐渐发生的，并且牙齿和颌骨尺寸的变化基本上与之相适应。
But with the more recent revolutions in agricultural and culinary habits, that relationship changed.
但随着农业和烹饪习惯的更近期革命，这种关系发生了变化。
As the theory goes, over a relatively short period, some human populations saw a decrease in jawbone size, while teeth stayed roughly the same size, meaning they're left vying for limited space.
根据该理论，在相对较短的时间内，一些人类群体的颌骨尺寸减小，而牙齿尺寸基本没变，意味着它们要争夺有限的空间。
When they do grow in, they may displace others and get jostled into some eccentric positions.
当它们长出来时，可能会造成其他牙齿移位，并被挤到一些奇怪位置。
And then wisdom teeth, which are usually the last to make their debut, seem to only complicate things further.
而通常最后露面的智齿似乎只会让情况更复杂。
In many cases, they have little or no space to emerge.
许多情况下，它们几乎没有生长空间，
This can lead to impacted wisdom teeth, which may cause discomfort and infections if not surgically removed.
这可能导致阻生智齿，如果不通过手术拔除，可能会引起不适和感染。
So larger jaws appear to be associated with greater chewing demands.
因此，较大的颌骨似乎与更大的咀嚼需求有关。
And many scientists think that as people's diets have become less chewy, their jaws have gotten smaller—and that this has led to dental crowding, resulting in dental crookedness and impacted wisdom teeth.
许多科学家认为，随着人们的饮食越来越容易咀嚼，颌骨则越变越小而导致牙齿拥挤，进而导致牙齿歪斜和阻生智齿。
This hypothesis has been supported by some preliminary experimental data.
一些初步的实验数据也支持这个假设。
In a 1983 study, researchers raised 43 squirrel monkeys on diets of either naturally tough or artificially soft food.
在一项 1983 年的研究中，研究人员将 43 只松鼠猴分别喂养天然坚硬食物或人工软食物。
Those fed softer food had more crowded premolars, rotated or displaced teeth, and narrower dental arches.
吃较软食物的松鼠猴前磨牙更挤，牙齿扭转或移位，而且牙弓较窄。
And a 2004 study similarly observed that hyraxes raised on cooked foods experienced roughly 10% less growth in facial areas involved in chewing compared to those given raw and dried foods.
2004 年的一项研究也观察到，与吃生干粮的蹄兔相比，吃熟食的蹄兔面部咀嚼部位的生长速度约降低了 10%，
In other words, the issue at large seems to be environmental—or one of lifestyle—instead of a genetic one, though heritable factors may be at play in some instances.
换句话说，整体问题似乎是环境或生活方式问题，而非遗传问题，尽管在某些情况下可能存在遗传因素的作用。
It’s estimated that somewhere between 30 to 60% of people today experience some level of tooth crowding.
据估计，今天约有 30%～60% 的人口存在不同程度的牙齿拥挤问题。
But this trend varies across global populations.
但这一趋势在全球人口中存在差异。
Some people naturally never have wisdom teeth.
有些人天生就没有智齿，
And some don’t experience tooth crowding or crookedness and still get their wisdom teeth without a hitch.
有些人不会出现牙齿拥挤或歪斜的问题，仍可以顺利长出智齿。
This seems to coincide with diets that are less processed.
这似乎与较少加工的饮食相吻合，
So how can we prevent tooth crowding early, using lifestyle changes and orthodontics?
那如何通过生活方式改变和矫正牙齿来早期预防牙齿拥挤呢?
Well, it’s certainly something to chew over.
这确实是一件值得深思的事情。
