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

「為什麼我要刷牙？」這類的問題，而且幾乎是每個晚上，

Right around, say 8 o'clock.

大概在八點左右吧

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

這個問題常常都是這些人 10 歲以下的小孩在問的

And in those instances, the answer almost always is

在這些情況下，答案通常是，

"Because your mother and I told you to!"

「因為你媽我叫你這麼做！」

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

但我們一位在 Tumblr 地追蹤者以不同角度問了同樣的問題，

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

「從演化觀點來看，為什麼我要刷牙？」

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

答案還是一樣，「因為你媽我叫你這麼做！」

Okay, actually, it is a pretty cool question.

好啦，其實這是個很酷的問題

Cause our primate ancestors didn't brush their teeth,

因為我們的祖先並不刷牙，

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

而且他們也沒有因此滿地掉牙或死於齒齦炎

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

是吧？嗯，的確是有一些人，但也不是大家都這樣啦

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

我的意思是，所有有牙齒的動物某種程度而言都可能會有牙齒的毛病

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

獸醫會告訴你他們常常在幫貓狗處理蛀牙，

or caries, as scientists call them.

科學家稱之為龋病

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

生物學家們證實許多野生動物，如獅子、熊、鯨確實會受口腔潰瘍折磨

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

但為何我們要刷牙，有部分的原因其實和長壽有關

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

大部分的野生靈長類不夠長壽，因此牙齒和牙床的疾病不太會在牠們有生之年出現

We do.

但我們會！

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

例如，演化上和我們親緣最近的大猩猩，在野外的壽命大約為 40 年，

In captivity, though, it's around 60.

豢養的則為 60 年

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

蛀牙可能成為人工飼養猿、猴的問題，

which is why keepers have to regularly brush their teeth.

這也是為什麼飼主需要定期為牠們刷牙

Which I imagine is not super fun.

在我看來可一點也不好玩

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

我們人類的壽命在大部分工業化國家約為 80 年，

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

比我們演化上的近親還要多出一倍

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

所以我們要用心維護我們的牙齒，讓它們的工作壽命跟著我們一起延長

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

一也就是說，天之內你得刷好幾次牙

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

把這點想成是你為演化帶來的利益所付出的一點小代價吧

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

但除此之外，還有一個影響我們口腔健康的重要因素，

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

和我們的祖先截然不同，那就是我們的飲食

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

靈長類以水果、種子、堅果、樹葉為食

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

黑猩猩偶爾也會吃昆蟲或一些肉

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

從人類在 12,000 年前開始種植穀類後，

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

我們的飲食變成以穀類中含有的澱粉與其他簡單醣類為主

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

蛀牙的細菌和我們一樣都偏好這些醣類，

they are a very readily accessible form of energy.

因為這些醣類可以快速被吸收並產生能量

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

所以說，你吃越多糖，你就越容易蛀牙

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

這不只是針對那些萬聖節剩下的糖果和可口可樂，

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

還有那些你可以想到的穀類，像是小麥、燕麥或玉米

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

蛀牙和農業在演化上的關係是如此特殊

In fact that anthropologists can actually determine

人類學家們還可以

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

藉由蛀牙毛病，來確切地指出該文明的農耕生活是從什麼時候開始發展

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

再說一次，這只是我們為成功演化成如此棒的物種所付出的一點小代價

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

現在，說真的，去刷牙！然後上床睡覺去！已經很晚了，你明早還要上學啊！

Thanks for watching this SciShow Quick Question.

感謝你收看這集的 SciShow Quick Question

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

如果你有任何問題希望我們為你解答，

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

你可以到我們的 tumblr、facebook、 twitter，或直接在影片下留言發問

And if you want to keep getting smarter with us,

如果你想要和我們一起長知識，

you can go to youtube.com/scishow and subscribe.

那就到 youtube.com/scishow 訂閱我們的節目吧！