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Uploaded:2017-03-11
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A lot of humans need or want braces to fix their crooked teeth, but why do you never see a dog walking down the street with headgear? Our ancient ancestors and mac and cheese may be to blame!

*Correction: Even though hyraxes look similar to rodents, they're actually in the order Hyracoidea, not Rodentia! They're more closely related to elephants and manatees than to mice and guinea pigs.*

Hosted by: Hank Green
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Sources:
https://www.wired.com/2011/11/agriculture-jaw-shape/
http://www.pnas.org/content/108/49/19546
http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0117301
https://www.ncbi.nlm.nih.gov/pubmed/19514263
http://www.sciencedirect.com/science/article/pii/S004724840400051X
http://rspb.royalsocietypublishing.org/content/early/2011/06/07/rspb.2011.0971
Hank: You might need to go to the dentist for a bunch of reasons, from filling cavities to wisdom tooth surgery. A lot of us have overcrowded or crooked teeth and need or want braces to straighten them out. But you don't see other species and think "oh man that beavers teeth sure could be straighter."

So why are we so prone to crooked smiles? Well it turns out there's just not enough space in our modern human jaw for all of our teeth to fit in easily. But it wasn't always this way, in fact the problem might be linked to the rise of Agriculture around 10,000 years ago.

Growing vegetables and raising animals went hand-in-hand with a big increase and how much humans processed their food, like cutting it into smaller pieces or cooking it. This made food much easier to eat, so we didn't need as much chewing and biting power. According to some anthropological evidence, this also meant that our jaws shrank, but the number of teeth we had a stayed the same, leading to the orthodontic woes of today.

One study looked at skulls from before, during, and after the transitions to agriculture in the Middle East and found changes in the jaws. Jaw bones from pre-agricultural times showed a lot of wear and tear on the teeth from intense chewing, but very little crowding. After farming though, jaws became wider and shorter front to back, and they had more crowded crooked teeth.

Another study compared the skull and jaw shapes of 11 modern human populations from around the world, including some farmers and some hunter-gatherers, and the hunter-gatherers had longer, narrower jaws, especially lower jaw, than the farmers, which are better for intense chewing. These changes in our jaw shape might not be because of changes in our genes though. It's not necessarily natural selection at work, where the farmers with shorter jaws were more likely to survive, instead this might be an example of what evolutionary biologist called developmental plasticity: an organism's potential to grow in different ways depending on its environment.

A study on small rodents called hyraxes, for example, found that animals raised on softer, cooked food, instead of raw or dried food, had less growth in the bones of their jaws and lower faces. It's hard to test this directly in humans though, because that would mean limiting what people could eat for a huge chunk of their lives. But it's possible that each of us could develop a bigger stronger jaw we only a tough foods while growing up. So our love of warm cooked meals from tender meats to mac and cheese might have doomed some of us two years of braces.

But in the long run if we're talking like a few overcrowded teeth or like chewing your food forever until your teeth break... I'll take the first one, especially if it's got mac and cheese!

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