Name: 実は”役立たず”な体の部位は？進化生物学者が解説 | WIRED Japan
Uploaded: 2025-01-30T08:45:33.000Z
Duration: 11 min
Description: Thousands of YouTube videos with English-Chinese subtitles! Now you can learn to understand native speakers, expand your vocabulary, and improve your pronunciation...

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We're gonna take a look, starting at the head and going all the way down to the toes at some of the most interesting body parts that have often been categorized as maybe useless.

Some people have muscles where they can wiggle their ears a little bit.

So these are remnant auricular muscles that originally had great functions, particularly with sound, the way your dog or your cat do.

Even in many of the monkeys, our ancestors' ears are able to move a bit with sound, but now they've largely lost that function and they are usually considered vestigial.

The term vestigial comes from the Latin meaning footprints.

So there are structures that were thought to be sort of footprints in time, giving us little clues to what came before.

So we, when we hear a sound, do not necessarily move our ears in that direction.

We tend to move our entire head towards the sound.

What's interesting to show that it's still hooked up, studies have shown that when we hear a sound, the brain areas that deal with these muscles have some activity.

When you look at the medial side of the eye area, you're going to see a vertical line.

Next time you look at a dog or a cat or a reptile, you'll notice that they don't have two, but they have three eyelids.

We know we don't have it in our closest relative, the chimp, and we don't have it in ourselves.

And apparently we have sufficient moistening without needing that.

Wisdom teeth, technically known as our third molars.

You can see here, they're largely problematic in which they bend or twist.

And you have to go to the oral surgeon to have them removed.

Over the eons of our evolutionary changes, our diet became very varied.

The molars are grinding teeth for eating leaves and vegetable type things.

And you can see how the face is very forward in a gorilla.

In the course of human evolution, our face became very flattened in.

Our molar teeth became shoved all the way back.

We developed a very, very pronounced chin found only in Homo sapiens.

It's a distinguishing feature of our species.

And we're not exactly clear what made it come about.

Sometimes things occur in our body that had no discrete meaning or function.

Nipples are extremely important structures.

By the way, for example, dogs and cats, they have multiple nipples.

There's a developmental ridge where nipples appear.

Nipples can appear all along a series of lines.

And you may find, for example, that somebody has a nipple all the way down in the pelvis.

Or frequently in the armpit is a bit of a throwback.

And that term is usually used for something that has missed a few generations or something that pops up due to an interesting recombination of genes.

But our hair is not densely packed all over like our closest relatives.

Hair's prime function is for thermoregulation.

And it played a very vital part when our ancestors came from forest-like environments, helping to keep heat in.

Things were shifting on the plains of Africa.

And our ancestors started to go to savannas.

And the loss of hair helped us in our active lifestyles with sweating.

The glands involved in sweatings are much greater in us.

And it allows us to maintain our temperatures better.

Hair in our furry relatives had a purpose with little babies being able to hang on to it.

We think we still maintain the little grasp reflex of newborns.

Certain areas in primates, particularly apes, became hairless early on.

We do retain some hair on the top of our head, in our anogenital area, and in our armpit area.

Hair up there aids in cooling the area and protecting it.

Erector pili muscles produce the effect of goosebumps.

What they do when they're stimulated is they contract.

It'll aid in the skin responding to some type of threat.

You'll get the hair stand up in the back of your neck.

When this occurs in our ancestors, or your cat, the hair will become puffed up.

It increases the appearance of your size, so it's a display feature as well.

This is called the cecum, and this worm-like structure coming off of it is known as the appendix.

It's very useful, because it was removable.

The appendix was thought to be vestigial.