Name: 乳糖耐性の進化 - HHMI BioInteractiveビデオ (The Evolution of Lactose Tolerance — HHMI BioInteractive Video)
Uploaded: 2021-01-14T06:00:20.000Z
Duration: 15 min 5 s
Description: VoiceTubeの動画で発音を聞きながら英語表現を覚えよう！学べる英語：

But from the time our species   evolved some 200,000 years ago,

people started domesticating   animals for food,

living in settlements,   and cultivating crops.

These cultural changes had   profound biological impacts

And you're about to encounter   one surprising example.

Almost all of us can   digest it as babies.

But the story of how   many adults can use it

as a food is a fascinating   case study--

a study of the co-evolution   of human culture and biology.

In fact, producing milk   for babies is a key trait

that distinguishes mammals from   all other types of animals.

can't easily pass through   the intestinal wall.

So cells here make an   enzyme called lactase,

which breaks lactose into   glucose and galactose.

These two simpler sugars can   then enter the bloodstream

Around the time young   mammals stop drinking milk,

almost all of them   stop making lactase,

so they lose their   ability to digest milk.

What typically happens when   an adult mammal drinks milk?

through the small intestine   to the large intestine.

and can cause cramps,   gas, and diarrhea.

It's a bad idea to offer a   bowl of milk to an adult cat.

in which some adults can drink   milk without getting sick.

Not all of us, but   worldwide, about a third

This minority is called   "lactase persistent"

because their ability to   produce the enzyme that breaks

down lactose persists   beyond childhood,

How did lactase persistence   come about?

Geneticist Dallas Swallow   will show me how to figure

out whether someone can   digest the sugar in milk.

[SWALLOW:] You're going to   do a lactose tolerance test.

[SWALLOW:] The idea is   to look to see what the level

of the volunteer before the   lactose load has been taken.

[WELLS:] After measuring   my baseline glucose level I now

[WELLS:] If my body   is still making lactase,

After I drank the milk,   here's what happened.

No doubt about it: My lactase   enzyme is still working.

[SWALLOW:] Where do   your family come from?

[WELLS:] Britain on   my father's side, Denmark,

[SWALLOW:] You can see   first of all that most people

[WELLS:] My family   background makes sense.

In only a few regions   is a large majority

In other parts of the world few   adults easily digest lactose.

To get a clue, researchers   looked at DNA.

They first compared the   part of the lactase gene

that encodes the   enzyme across persistent

We know that genes, including   lactase, are regulated--

by other pieces of DNA   that act like switches.

In search of a possible   mutation in a lactase switch,

a research team identified   Finnish families

that had members who   were lactase persistent,

Statistical geneticist   Joe Terwilliger was part

[TERWILLIGER:] We then   looked to see if they shared DNA

that we knew was affecting   the metabolism of lactose.

[WELLS:] On chromosome 2,   in and around the lactase gene,

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乳糖耐性の進化 - HHMI BioInteractiveビデオ (The Evolution of Lactose Tolerance — HHMI BioInteractive Video)

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