(Justin) There's also some other landmarks we need to point out...
(Jonathan) Hold on.. ready! Clinched!
(Justin) Such as right here...
(Jonathan) Why do humans have the biggest butts in the animal kingdom?
Is it because the gluteal muscles? The fat? A combination of the two?
Is it because we sit on them all the time?
I'm Jonathan Bennion with the Institute of Human Anatomy, and we're going to take a look
at real human butts — on the cadavers — to see why these things are so huge.
So let's do this!
So first, what do I mean by, "humans have the biggest butts in the animal kingdom?"
You might say, "well Jonathan, have you ever seen an elephant's butt?"
Well what we're talking about here is a butt-to-body size ratio.
So if you were the size of an elephant, your butt would be huge.
Or in other words, you'd have quite the booty.
Speaking of booty, what's the true name for the butt?
Because there are a ton of different slang terms...
ass, backside, behind, booty, bottom, breach, bum, buns, caboose, can, derriere, duff,
fanny, fundament, haunches, hiney, hindquarters, hunkers, keister, rear, rump, seat, tail, tush...
and many more — which you should post in the comments after you hit the like button...
So in order for us to go over the true names of the butt,
we need to see a real butt on a human, to go over the surface anatomy.
So Justin!
(Justin) Yes Jonathan?
(Jonathan) As you probably heard right there, we need a real human butt.
(Justin) I know — that's why we have Geoffrey.
(Jonathan) Geoffrey is a real human skeleton who does not
have a real human butt — that's the definition of a skeleton...
(Justin) I can already see where you're going this, and you are NOT going to use my butt.
(Jonathan) Fine!
(Justin) Oh (bleep) no!!
(Jonathan) Do you want to be the one in the tights? These are a little confining...
(Jonathan) Why are you putting gloves on?
(Justin) Dude, I am so past my comfort zone right now, this is necessary.
(Jonathan) External anatomy — not internal anatomy. We're clear on that, right?
(Justin) I'm very aware. This pencil is to keep literally
as much distance between you and me as possible.
(Jonathan) Fine. As long as we're good on external anatomy, we're fine...
(Justin) Alright... so there are different names for this region that we could use.
You could call this the gluteal region.
You could call it the cluneal region if you wanted to.
If you're fancy, you could even say it's the bu-ttah-cks, or the bu-ttah-ck,
but I typically just say buttocks, or buttock.
But there's also some other landmarks we need to point out..
(Jonathan) Hold on.. ready! Clinched!
(Justin) Such as right here... this is called the gluteal fold.
Then, right dead center, is what's known as the gluteal
cleft — or in this instance it's literally Jonathan's butt crack — that's great...
But this entire region also has some other anatomy, such as skin, connective tissue,
fatty tissue, and then deep to underneath — or deep to all that, is going to be muscular tissue.
(Jonathan) Which is really awesome because we have a dissection on a cadaver to show you those
layer by layer, to show you all those tissues that make up our big butts.
(Justin - Off Screen) That's why we use the cadavers in the first place, Jonathan...
(Jonathan) He'll be fine don't worry about him.. he'll be fine..
So finally we get to take a look at an awesome dissection that will help us understand why
humans have a big gluteal region or big butts, and we'll see layer by layer, here.
So take a look here, you can see this is the back side — or the left butt cheek,
you could say — on a real human cadaver.
And we're going to see the layers here.
And the first layer that I'm going to pinch is the epidermis and the dermis, which
you can see is not contributing a ton to the thickness of the gluteal region.
But when we go down to the next (layer), you can see this layer, this is called the hypodermis,
also known as the subcutaneous layer.
Now this is made of fatty tissue or adipose.
And you can see on this particular cadaver it's
about an inch — about an inch thick — on some people, it can be even thinner.
On others it can be up to inches thick, so quite the variable layer.
And often when I talk to students in the classroom about,
"hey what do you think the reason for humans having big butts is?"
They often go to this layer here, called the hypodermis.
The funny thing is, this is still not the reason why humans have big butts!
So if it's not the adipose or the hypodermis that makes humans butts
so glorious then it has to be this guy underneath, called the gluteus maximus.
The name kind of implies its size, right?
The gluteus maximus — by most measurements — is the largest muscle in the human body,
and the reason why you have a big butt.
Now I mean if you compare it to this other dissection here,
which I'll show we've removed here, you can see there's a lot of girth and size to this thing.
It's always interesting when we talk about things in science,
and anatomy, and biology, and things of that nature, because
often when we answer one "why?" — for example "why do humans have big butts" — and the answer being,
"because the gluteus maximus is so large" — it often creates another question..
"Well, why is gluteus maximus so large in humans?"
That answer comes down to how the gluteus maximus functions with how we walk and how we move.
So let's go talk about some walking!
Understanding why the gluteus maximus is so large also requires a little bit of
understanding of how it attaches to the skeleton, and mobilizes the hip joint.
So we are going to use Geoffrey here — no, he does not have a gluteus maximus, as we've established
earlier in the video — but we can see where the gluteus maximus attaches to on the skeleton.
So if you take a look at this red paint here,
this is one of the attachments on this bone that we refer to as the ilium.
Another one is on the sacrum, which is the lower part of the spine,
and then down on the femur you can see this blue marking that's where it inserts.
Some of the fibers even go into the IT Band.
So, because it attaches from these two bones down to the femur,
it's going to mobilize the joint in between, which is simply just the hip joint.
What does that action look like, or what is it specifically called?
Now the gluteus maximus does what we call, extension of the hip.
You can see what it looks like on me, and even with the bones here.
Even if you were to step up on something like when you were hiking,
pulling back and down, this is called extension
But what if your foot is fixed to the ground?
Can your gluteus maximus still create some extension?
The answer is yes!
Think of like a deadlift position, like so.
My foot's fixed to the ground, but where my movement comes from
is the pelvis rather than the actual femur itself.
So if I move down like this, and I come up to an upright position, that's also extending the hip.
So you can do extension this way, or this way, and I end up in the same position, which is
upright in a bipedal position, which is how humans stand in an extended position.
So think about how cool that is!
The gluteus maximus is always buzzing — activated — to keep us in this upright extended position.
If you compare that to your cute little dog or your cute little cat at home,
they're quadrupeds, and they're in a flexed position so their gluteus maximus
doesn't have to engage all day long just to hold them in an upright position like it does with us.
And one last thing I want you to consider from this bipedal position...
When you walk, run, or go on a full-fledged sprint,
the gluteus maximus has a really important job, again to maintain this upright position.
Think about this — when you plant when you're sprinting or running as fast as you can, this
whole upper body — the weight and the momentum of your upper body — actually wants to fall forward.
But gluteus maximus — because it's attached to that pelvis — is like unh
unh — and helps pull you and keep you upright so you don't fall on your face
when you're running, jogging, or frolicking through the forest as a happy bipedal human being.
Thanks for watching our video on why humans have big butts!
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