Those with the mutation produce lactase throughout their lives.

有这个突变基因的人一生都可以生成出乳糖酶。

And for most of history, humans stopped producing lactase after childhood.

从人类的发展上看，大况下，人类过了儿童时期就不会再生成乳糖酶了。

But the older we grow, the fewer lactase enzymes our body produces.

但是，随着年龄的增长，人体产生的乳糖酶越少。

This so-called lactase persistence trait probably spread as Neolithic groups trekked north and west through Europe.

这种所谓的乳糖酶持久性特征可能随着新器时代的群体在欧洲向北和向西跋涉而传播。

This adaptation has to do with a specialized enzyme: lactase.

乳糖酶。

That one exception is humans, but like every other mammal, will still hardwired to stop producing lactase after infancy.

人类是个例外，但就像其他哺乳动物一样，在婴儿期后仍会停止分泌乳汁。

And the lactase that so many of us don't have, is one of these.

很人所缺乏的乳糖酶就是其中之一。

And those bacteria possess about 1000 different kinds of enzymes of their own, including lactase.

这些细菌拥有大约 1000 种自己的酶，包括乳糖酶。

These are maltase, sucrase, and lactase, which break down the short chains of sugars called oligosaccharides into simple sugars, called monosaccharides.

它包括麦芽糖酶、蔗糖酶与乳糖酶；它能将称为寡糖的短链聚合糖分解成简单糖类，或称单糖。

Lactase is made in the small intestine.

乳糖酶在小肠中产生。

I never go anywhere without my Lactaid, fast acting lactase enzyme.

- 如果没有的 Lactaid，速效乳糖酶，绝不会去任何地方。

If there's no lactase in your small intestine, you can't digest the milk.

如果你的小肠里没有乳糖酶，你就无法消化牛奶。

So once you consume milk, you're producing lactase, the lactose enters into your small intestine and it's digested.

所以一旦你喝了牛奶，你的身体就会产生乳糖酶，乳糖进入小肠并被消化。

When we're babies, our bodies produce lactase so we can digest breast milk.

当是婴儿时，的身体会产生乳糖酶以便消化母乳。

The fact that some populations around the world continue to produce lactase into adulthood is actually a derived trait.

世界上有些人群在成年后仍然能够产生乳糖酶，实际上这是一种衍生特征。

And yet, people in Mongolia today do not have the ability to produce lactase as adults.

然而，当今蒙古国的成年人并没有产生乳糖酶的能力。

To digest it, you need a specific enzyme called lactase.

要消化它，你需要一种特定的酶，叫做乳糖酶。

Lactose is basically milk-sugar that can only be digested with the help of a special intestinal enzyme — lactase — which many adults do not produce enough of.

乳糖基本上可以说是奶糖——只能在一种特殊的肠道酶乳糖酶的帮助下消化，而许成年人无法产生足够的乳糖酶。

Different enzymes help to break different linkages - for example amylases break down large polysaccharides like starch into smaller units, whereas lactase, sucrase, and maltase break down lactose, sucrose, and maltose into their monosaccharides.

不同的消化酶能分解特定的糖链，比如淀粉酶可以将淀粉等糖分解为小分子的糖，而乳糖酶、蔗糖酶、麦芽糖酶则分别可将乳糖、蔗糖、麦芽糖降解为相应的单糖。

Those of us who can't produce the enzyme lactase in our small intestine simply let milk and cheese pass through the organ untouched, leaving the digestion to these bacteria in the large intestine.

这些不能在小肠中产生乳糖酶的人只是让牛奶和奶酪原封不动地通过器官，把消化留给大肠中的这些细菌。