Name: 人間に尻尾がない理由 (Why Humans Don’t Have Tails)
Uploaded: 2021-01-14T08:13:47.000Z
Duration: 3 min 16 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：

様態の副詞

Basically, everyone has them: fish, birds,

程度の副詞

most reptiles, and even some of our closest relatives.

Since tails first evolved at least 500 million years ago,

and rattlesnakes use them to scare off predators.

But for most mammals, they serve one major purpose:

Yet, as you get closer to humans on the evolutionary tree,

tails disappear. Gorillas don't have them,

To understand why, take a look at how we walk.

Some of us primates crouch with our chest held diagonally

to the ground. Others like gibbons and humans

Now, walking like this gives us a huge advantage

which have to pour energy into every step they take,

we use around 25% less energy than walking on all fours.

And in the wild, every ounce of energy you save

can mean the difference between survival and starvation.

But this way of getting around also totally

it sits on top of the body when you walk,

not in front, so you don't need a tail as a counterbalance.

That being said, you can still see a reminder

of a time when our ancient primate ancestors had one.

and, yes, it's sad and pathetic, and you can't wag it.

Most often, these tails are actually tumors,

outgrowth of the spine but are completely boneless,

a soft tube made entirely of fat and tissue.

These types of tails usually form as a birth defect,

a deformity of the spine called spina bifida.

And in these situations, doctors will surgically

remove the tails with no harm to the baby.

But as cool as it might sound to have an extra limb

to swing through the trees or keep mosquitoes away,

we are who we are today because, well, we don't.

字幕リスト動画再生

人間に尻尾がない理由 (Why Humans Don’t Have Tails)

eliminate

basically

ancient

evolve