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  • There's a certain set of humans in the world that hears the

  • "Why do I have to brush my teeth?" question pretty much every evening.

  • Right around, say 8 o'clock.

  • Almost always posed by the offspring of that person. Usually under the age of 10.

  • And in those instances, the answer almost always is

  • "Because your mother and I told you to!"

  • But one of our followers on Tumblr asked a more thoughtful version of this same question:

  • "Why do I have to brush my teeth from an evolutionary perspective?"

  • The answer is still because your mother and I told you to!

  • Okay, actually, it is a pretty cool question.

  • Cause our primate ancestors didn't brush their teeth,

  • and surely they didn't have their teeth falling out all over the place, and they weren't dying of gingivitis.

  • Right? Right. Well some of them did, but not all of them.

  • I mean all animals that have teeth likely have to deal with tooth decay to some extent.

  • Veterinarians will tell you that they see cats and dogs all the time that have cavities

  • or caries, as scientists call them.

  • And biologists have reported finding wild animals as diverse as lions, and bears, and orcas with huge painful abscesses.

  • But part of why we have to brush our teeth has to do with longevity.

  • Most wild primates just don't live long enough for things like tooth and gum disease to catch up with them.

  • We do.

  • For example, the life expectancy of our nearest evolutionary relative the chimpanzee is just 40 years in the wild.

  • In captivity, though, it's around 60.

  • And tooth decay can become a problem with captive apes and monkeys,

  • which is why keepers have to regularly brush their teeth.

  • Which I imagine is not super fun.

  • Our life expectancy, meanwhile, is around 80 in most industrialized countries,

  • which means we're living twice as long as our closest genetic relatives.

  • So we gotta keep our parts working for a lot longer than they were probably supposed to work.

  • And this means brushing your teeth a couple times a day.

  • Consider it a small price to pay for having benefited so much from evolution.

  • But beyond that, by far the most important factor that affects our dental health,

  • as opposed to that of our genetic predecessors, is our diet.

  • Most primates live quite nicely on diets of fruits, and seeds, and nuts, and leaves.

  • And in the case of chimps, the occasional insect or piece of meat.

  • But since we started cultivating grain some 12,000 years ago,

  • our diets have become totally dominated by starches and the simple sugars that they contain.

  • The bacteria that form cavities really love these sugars, and for the same reason that we do:

  • they are a very readily accessible form of energy.

  • So the more sugar you eat, the more susceptible you are to tooth decay.

  • And this is true not just for leftover Halloween candy and Coca-Colas,

  • but any kind of cereal grain you can think of like wheat, or oats, or corn.

  • The evolutionary connection between tooth decay and agriculture is so distinct.

  • In fact that anthropologists can actually determine

  • whether a culture started farming in part by studying when they started to get cavities.

  • Again, it's just part of the cost of being such an awesomely successful species.

  • Now seriously, brush your teeth! Go to bed! It's late; you got school in the morning!

  • Thanks for watching this SciShow Quick Question.

  • If you have a question that you would like us to answer,

  • you can ask us on our tumblr, or our facebook, or our twitter, or in the comments of this video.

  • And if you want to keep getting smarter with us,

  • you can go to and subscribe.

There's a certain set of humans in the world that hears the


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B1 中級

なぜ歯を磨かなければならないのか? (Why Do I Have to Brush My Teeth?)

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    SylviaQQ に公開 2021 年 01 月 14 日