Selects: Does the body replace itself?

Does the human body really replace itself every few years? The answer is yes, but different parts of the body do so at different rates. Learn all about which parts of your body are the speediest, and which take the longest to regenerate, in this classic episode.

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Episode Transcript

Speaker 1 (00:00):
Hey, everybody, it's your old pal Josh for this week's select.
I've chosen Does the body replace itself every seven years?
Sounds like a medical episode, and it kind of is.
But after a little while it turns into a brainbuster
of a head scratcher of a philosophical bent that I
think you're gonna love. I hope you enjoy the living.

Speaker 2 (00:18):
Heck out of it.

Speaker 3 (00:24):
Welcome to Stuff you Should Know, a production of iHeartRadio.

Speaker 1 (00:33):
Hey, and welcome to the podcast. I'm Josh Clark with
Charles W. Chuck Bryant and guest producer.

Speaker 2 (00:38):
Nol Knowle's in the house.

Speaker 1 (00:41):
It's the it in the new studio. Yeah, man, this
place is comfy, cozy. I like it.

Speaker 3 (00:47):
I wish I'm I don't know, I wish there was
a chair version of a waterbed.

Speaker 1 (00:52):
I know this is a napish little place.

Speaker 3 (00:54):
Yeah, especially today, I think I'm dragging all apologies.

Speaker 1 (00:59):
Yeah, same here. So if we're talking kind of slow
or low, or we just stopped talking for a little while,
it's we're as tired.

Speaker 2 (01:07):
Yeah, bumped into you at the Hawks game last night.

Speaker 1 (01:10):
I know, Hey, how many is that?

Speaker 2 (01:11):
You know? Yeah, just at the bump in yep.

Speaker 1 (01:15):
We were both at the Hawks gaming and the Hawks.

Speaker 3 (01:16):
One didn't even know we were going. Look over in line,
there's Josh and Yumi. Yeah that's great. There's Chuck and Eddie.
Yep in an arena of eighteen thousand bumping into someone?

Speaker 2 (01:31):
Is that it?

Speaker 1 (01:31):
That's all it holds?

Speaker 2 (01:32):
I think it's something like that. It's a good lot
of people.

Speaker 1 (01:35):
It's a good arena.

Speaker 2 (01:36):
Yeah. But you had box seats because you're special.

Speaker 1 (01:38):
They were free out.

Speaker 2 (01:40):
Mine were free to in. The nose bleeds.

Speaker 1 (01:43):
I liked just about every seat in that place.

Speaker 2 (01:45):
Yeah, it's not too bad. I was.

Speaker 3 (01:46):
I was laughing about the nosebleeds going in, But then
I got up there.

Speaker 2 (01:51):
I was like, this is great. Yeah you can see everything.

Speaker 1 (01:53):
Did you nose actually bleed just twice?

Speaker 3 (01:56):
Yeah, once out of its sheer excitement and then once
from the altitude and that was more of a spray,
rightah yeah.

Speaker 1 (02:05):
Just covering everyone that was like go Hawks.

Speaker 2 (02:08):
Boy, what a weird intro.

Speaker 1 (02:09):
It's a little weird, but I mean it kind of
jibes a little bit because we're talking. Yeah you're mentioning blood.

Speaker 2 (02:18):
Sure, it was shedding cells and blood.

Speaker 1 (02:20):
You were like, blood is made up of cells and
we shed tons of cells. But before we get to that, right,
there's the fact that the podcast you shed cells. I
want to mention this one thing I read. Yeah, it's
called I think the title of the article is the
Self is Moral. It's about like where we get our
identity of self from, like where it's rooted. It was

(02:42):
written by a person named Nina Stromyer. I believe it
was on AON magazine. Yeah, just type in the self
is Moral aon it'll come up.

Speaker 2 (02:50):
I'll get you there.

Speaker 1 (02:52):
Uh. And towards the beginning, the author says, there's this
very famous philosophical exercise, which you know, philosophers love to do,
like mental exercises.

Speaker 2 (03:04):
Yeah, that's what that's all they hashened.

Speaker 1 (03:06):
So imagine you have like a kind of imagine you
have like a ship, right, like a boat. Yeah, a
nice Yankee clipper, okay, okay. And this Yankee clipper is slowly,
over time kind of salvage for parts. But rather than
just being stripped, like every time a part is taken out,

(03:26):
it's replaced, and then over the course of like fifty
one hundred years, is each plank, as each bolt, as
each like mast head, even the thing. The carved lady
in front eventually just gets replaced with something else.

Speaker 2 (03:41):
Yeah, a new carved lady that speaks of the time.

Speaker 1 (03:44):
Right, you know? Is it still though, after every single
part has been replaced, the same ship that it was before?

Speaker 2 (03:52):
Yeah? I see what you mean. I don't think that
can be possible.

Speaker 1 (03:58):
Why not, especially if it has the same name and
it's the same ship in the same place as before.
It was just slowly, over time moved out. True, where
does the self lie?

Speaker 3 (04:10):
Yeah, that's a good point, man, Like redoing a house,
same thing, Yeah, I mean, like they saw the floors
and the walls and the windows, Like, when does it
cease to become that same house that was built in
nineteen thirty exactly.

Speaker 1 (04:22):
Isn't that cool?

Speaker 2 (04:23):
Yeah? It is really cool.

Speaker 1 (04:24):
And the reason that it applies to this episode is because,
over the course of your lifetime, a significant portion, pretty
much all of the cells in your body are going
to be replaced. Yeah, so that the person even after
you reach your adult self. Yeah, physically, by the time

(04:46):
you die, assuming you're gonna die much later, you are
essentially a different person, at least on the cellular level.

Speaker 2 (04:55):
Yeah, thirty seven trillion cells.

Speaker 1 (04:58):
Ish that's how many we have.

Speaker 2 (05:00):
Yeah, that's what they estimate. And I did a little
looking into.

Speaker 1 (05:03):
Lifespans, like an estimate.

Speaker 2 (05:07):
Thirty seven trillion. Yeah, what do you want like to
like give or take?

Speaker 3 (05:10):
Yeah, I did a little research into lifespans just because
this all sort of comes back to like your death basically,
because that's all death is, is your your cells, you know,
dying little by little.

Speaker 1 (05:26):
Well yeah, I mean if you think about it, Chuck,
one of the things that.

Speaker 2 (05:29):
Like why do we die?

Speaker 3 (05:30):
If our we'll get to all that, Oh okay, but
it's intriguing, you know it is it started, you know,
questions started popping up. So apparently we gained about three
months every three months of life humanity every year that
we progress.

Speaker 1 (05:47):
Like the average life span spans by three months.

Speaker 3 (05:50):
Yeah, Like if you were born in twenty twelve, the
average lifespan is now and this is the United States,
is seventy eight point eight. If you were born in
nineteen oh one, it was about forty seven and fifty
years for men and women respectively. But if you look
at the ratio, it's still about three months. Despite all
our technologies, three months a year, every year, every year.

Speaker 1 (06:13):
Just slowly creeping along.

Speaker 3 (06:14):
Yeah, because I think the article it was like when
we're going to live to be one hundred by average,
and they say by the year twenty one hundred, if
things hold, then the average human or American will be
about one hundred years old.

Speaker 1 (06:26):
I thought that, so I guess that will if things
are steadily progressing. I had heard that like our generation
would be either the last or the first, the last
to not hit triple digits or the first two on average. Yeah.

Speaker 3 (06:41):
Yeah, I guess these are all gases, you know, so
who knows. Plus if you believe in like things speeding science,
speeding up?

Speaker 1 (06:51):
Yeah, what is that? Moore's law?

Speaker 2 (06:53):
Yeah? Is that it? Yeah, applied to computers, so in
that case.

Speaker 1 (06:56):
Right, right, but I mean you cantend it other stuff.

Speaker 3 (07:00):
Yeah, then you might think, you know it's it's but
you know, they say it's not increasing like that.

Speaker 2 (07:06):
No, at least not so far.

Speaker 1 (07:07):
Moore's law is exponential growth just adding three months every
year's yeah, non exponentials geometric. I think we're still at
non exponential growth definitely. Yeah, we're just adding three months. Yeah,
it's not bad though, that's pretty good average every four years.

Speaker 3 (07:23):
It's an extra year, yeah, well, and it's interesting to
think about. You know, people that were born you know,
a lot of our colleagues like eight years behind us,
are going to live an average of.

Speaker 2 (07:34):
Two years longer.

Speaker 1 (07:36):
Yeah, that seems unfair, sad.

Speaker 2 (07:39):
Yeah, I know, what did they do to.

Speaker 1 (07:41):
Observe that we're we're thinking about our own deaths today? Yeah,
and chuck that there's this rumor theory, legend maybe okay,
that your body regenerates itself ninety percent of your body
regenerates itself every year.

Speaker 2 (08:01):
Yeah that's not true.

Speaker 1 (08:02):
No, it's not true, but it was a very long
standing rumor, and it was actually based on science. Yeah,
you know, not just the idea that, oh yeah, ourselves regenerate.
So back of the envelope estimate is that, you know,
we regenerate ninety five or ninety eight percent of ourselves
every year. It was early experimentation by injecting radioactive isotopes

(08:23):
into human beings, yeah, and then following their course and
then making estimates based on that led to this idea.

Speaker 3 (08:30):
It's called pulse labeling, is it. It's like tagging an
animal in the wild basically.

Speaker 1 (08:34):
Right, but you're just tagging a cell.

Speaker 2 (08:36):
Yeah.

Speaker 1 (08:37):
The specific types of cells.

Speaker 3 (08:38):
Yeah, they don't do that to humans anymore. No, it's
very animals. I think it's a very dumb thing to do.

Speaker 2 (08:43):
Sure, injecting radiation exactly.

Speaker 3 (08:45):
Yeah, unless, of course, you know it's radiation treatment that's true,
which is still a really weird thing if you think
about it.

Speaker 1 (08:52):
It's Yeah. I have a feeling it's gonna be like
one of the things we look back on.

Speaker 2 (08:56):
As like a primitive treatment. Yeah, yeah, yeah, I hope so.

Speaker 1 (09:00):
But there was this long standing science for decades or
this idea, scientific idea that we regenerated ourselves by ninety
five ninety eight percent. Finally, and I think two thousand
and five there was a a researcher named doctor Jonas Friesen.
He's Swedish.

Speaker 2 (09:21):
Dude's awesome.

Speaker 1 (09:22):
He said, this whole urban legend is really bringing me down.
I want to figure out a way to really track
how often the human body regenerates itself.

Speaker 3 (09:35):
Yeah, and the biggest question has been the brain, specifically
the cerebral cortex and the heart and the heart muscles.
I mean, they want to know all this stuff, but
those were the two biggest mysteries.

Speaker 1 (09:48):
I think, right, there's still the mysteries, but if you
went back to prior to two thousand and five, in
doctor Friesan's research, it was all a mystery. Yeah, he
figured out. He basically put a very act curate time
stamp on how often human tissue and human cells regenerate themselves. Right,
So the way he did this is very clever. For

(10:10):
a long time, botanists knew that the trees around the
world contained a spike of carbon fourteen radiation.

Speaker 2 (10:21):
Yes, thanks to humans and nuclear bombs.

Speaker 1 (10:23):
Exactly from nineteen fifty four to nineteen sixty three, tree
rings for tree growth around the world show a big
spike in carbon fourteen. Carbon fourteen is naturally occurring too,
So like just cosmic rays from the sun bombarred Earth's
atmosphere and create radioactive isotopes by knocking electrons from particles

(10:46):
in Earth's atmosphere, right, those radioactive particles become carbon fourteen,
which is radioactive, and in the atmosphere, carbon fourteen binds
to oxygen and creates carbon dioxide, which comes to Earth.
Every living thing breathes this stuff in, whether it's a plant,

(11:06):
whether it's a human like we just have see fourteen
in our bodies.

Speaker 3 (11:11):
We also eat plants exactly contain the sea fourteen besides
breathing it in.

Speaker 1 (11:15):
And we also eat the animals that eat the plants
that in just see fourteen. Right, So like we got
carbon fourteen in our bodies, that's right. But because of
the spike in carbon fourteen that was introduced to the
atmosphere from nuclear testing, there is a spike in humans

(11:38):
as well. So you can roughly age like a human
compared to another human if they were born in say
nineteen fifty nine, and one who was born in nineteen
seventy after there was that spike of carbon fourteen had
gone away. Right, that's pretty cool. But what doctor Friesen
did is even cooler. He basically went back to those

(12:00):
tree trunks, those tree rings that show a spike in
carbon fourteen, and created a calendar of carbon fourteen decay
and basically said, okay, on this date, this is how
much carbon fourteen was on Earth. And if I take

(12:20):
this cell and compare it, knowing that carbon fourteen decays
at a constant rate, I can tell you exactly how
old this cell is exactly. And he used it to
date cells and tissues and all sorts of cool stuff.

Speaker 3 (12:34):
Yeah, he was He went looking for a marker, and
he found one due to our atomic testing program, which
is pretty weird. You just released all that junk in
the atmosphere and now all these years later it has
a nice use.

Speaker 1 (12:48):
Yeah, you know it does.

Speaker 3 (12:50):
So we now know when we're going to die, right
sort of. And the reason he was able to use
this as a marker, Chuckers, is that when you take a.

Speaker 1 (13:00):
Breath of life, your first breath of life, that's right,
and you get some you get some of that C
fourteen into your DNA, and a steady amount stays in there,
like you don't keep ingesting C fourteen as far as
I understand, as far as your DNA goes, Oh okay,
once it's in your DNA, as your cells divide, that

(13:22):
original amount becomes divided evenly. So the less C fourteen
that's in tissue, the older that cell line is. Where
then the younger the actual cells are. Right, Is that right?

Speaker 3 (13:36):
I think so, which would mean the new cell the
marker would be a fresh batch of the C fourteen.

Speaker 1 (13:43):
No, it have less C fourteen.

Speaker 3 (13:45):
Oh really, yeah, let's say you have because the cell divided, yes, exactly, Yeah.

Speaker 1 (13:49):
Like you have ten grams of C fourteen, which you don't.
I can't imagine what that would be. Like. Let's say
your your one cell that's never divided has ten Yeah,
when it into two, it's each of those two cells
is going to have five grand and then two and
a half, and then one point seventy five and so
on and so on. So since you know that C

(14:10):
fourteen is generated at a constant rate, you know that
it decays at a half life of fifty seven hundred
and thirty years, you can look at the amount of
C fourteen and then also the decay of it as well. Yeah,
you can date things that are no longer living too,
to see when the when they ingested that C fourteen.

Speaker 3 (14:31):
Was Yeah, he's a little like a bingo card. He
just from the calendar that he made with the trees,
and he holds it up in the light, and that's
how he determines it.

Speaker 2 (14:39):
It's not true.

Speaker 3 (14:41):
But what he did determine though, was which is really cool,
And this is sort of what we've been building toward,
is that most of your cells are about seven to
ten years old, yes, in the body, and there are variances,
and of course we're going to talk about all that,
and right after this break, we're going to give you
a little primer on cells.

Speaker 2 (15:02):
So you know what all this means.

Speaker 3 (15:03):
Right, All right, Josh, were promised to sell primer, and

(15:28):
we like to deliver on those promises.

Speaker 2 (15:29):
Here stuff you should know.

Speaker 3 (15:31):
So I guess we started off by saying there are
thirty seven trillion cells about in the human body. Yeah,
give or take, give or take, and water makes up
about two thirds of.

Speaker 2 (15:43):
The weight of those cells. Oh yeah, that's right. They're tiny.

Speaker 3 (15:48):
You need a microscope to see them, and it's like
it's the tiniest thing that can still reproduce.

Speaker 2 (15:54):
Yeah.

Speaker 3 (15:54):
And even though we have many different kinds of cells,
I think two hundred types, and within those cells there
are differences, but there are a lot of similarities with
all cells in their structure. Namely, they have a cell membrane,
they have a nucleus, have a nucleus, some have more
than one. And these membranes are what allows nutrients to

(16:15):
pass in and out, waste to pass out water through
osmosis travels in reverse, osmosis travels out.

Speaker 1 (16:25):
Yeah.

Speaker 3 (16:27):
And what else, We got your mitochondria as well. That's
where this is the important, really important thing, which is
basically what keeps your cells alive.

Speaker 1 (16:35):
That's the power center, right.

Speaker 3 (16:37):
Yeah, and that's you know, your cells need food to
live just like your body does. But you can't pass
that that hamburger straight into your cell, right. It needs
to be broken down so your cell can use.

Speaker 1 (16:49):
It exactly into what adenosne triphosphate ATP is like the
universal cell fuel, right.

Speaker 2 (16:58):
Yeah.

Speaker 1 (16:58):
So there's a lot of stuff that the body does make.
I think you need like twenty three I think you
need twenty three amino acids, and like nine of them
your body doesn't really manufacture. So those are the nine
non essential amino acids, right. And you use amino acids
to build proteins, and use proteins for everything from making muscles,

(17:20):
to making red blood cells to you're mounting and immune response.
Proteins are very very vital in some of them you
have to build by eating stuff from your environment, right.

Speaker 2 (17:32):
Yeah.

Speaker 1 (17:33):
So you go out and you find yourself a nice
pig and you cut off its back leg. You say, sorry, pig,
here's a pig leg for you. But I need this leg.
I'm gonna eat this leg. And what I'm really eating
is the muscle. What I'm really really eating is the glutamine. Yeah,
and in my body's going to take this glutamine. It
can make it itself. But it doesn't hurt to have
an extra little bit of glutamine.

Speaker 2 (17:54):
Yeah, it does to have that pig leg And you're
exactly right.

Speaker 1 (17:57):
So I'm chomping on the pig legs. The pigs must
and listeners by the way, right, just use your imagination
for a second. Sure, And yes, I'm sorry too. So
you're eating the pig like and you're gaining this glutamine
as a result, and your body's metabolizing the glutamine and
then reusing it, right, And it can be glutamine, it
can be anything. If we're ingesting a protein, if we're

(18:21):
ingesting amino acids, if we're eating any kind of food, sugars, whatever,
our bodies break it down into its constituent parts, and
then a lot of those constituent parts become part of
our bodies. So if you think about it in this sense,
when we eat, when we breathe, we're taking in stuff

(18:41):
we need from the environment, and that stuff that we
take in from the environment becomes a part of us
literally physically on the molecular level, it becomes a part
of us.

Speaker 2 (18:51):
For better or worse, depending on what it is. Of course.

Speaker 1 (18:53):
Yeah, that's a great I think that's ultimately one of
the side lessons of this whole thing is we should
take care of ourvironment because that environment becomes us and
we either suffer or thrive as a result of it.

Speaker 2 (19:05):
You ever heard the expression you are what you eat?

Speaker 1 (19:07):
Exactly?

Speaker 2 (19:08):
Know, you literally are what.

Speaker 1 (19:09):
You eat, quite literally. And then also chuck, it goes
the other way as well. When we excrete waste, when
we exhale CO two that's taken up by other things
in the environment, is deposited into the environment and it
becomes part of the environment itself. So not only do
we regenerate our cells, regenerate tissue on average seven to

(19:33):
ten years, become almost wholly a new version of ourselves.
Were also the boundary between us and the surrounding environment
is really nonexistent because there's a constant exchange of molecules.

Speaker 3 (19:53):
Yeah, we lose on average, they say nine the average
adult male loses ninety six million cells per minute, But
we also replace those at the rate of ninety six
million per minute, yeah roughly.

Speaker 2 (20:09):
Yeah. Yeah, so that's the good news.

Speaker 1 (20:12):
So we've got all these cells that we're losing. We've
got all these new cells that are replacing them. And
I think, like you said earlier before the break, that
these the different types of cells and then hence different
tissues regenerate at a different rate, right.

Speaker 3 (20:27):
Yeah, And they all have specialized jobs, and the cells
are often built in such a way to aid that
job physically, you know, different to make that job easier.

Speaker 2 (20:38):
Which is really cool too, right, shows how versatile they are.

Speaker 1 (20:42):
Yes, you know, like stem cells are very versatile.

Speaker 2 (20:45):
Super.

Speaker 1 (20:46):
So let's say your skin, Yeah, your skin regenerates every
two to four weeks. I think, yeah, exactly, you get
a new healthy coating of skin every two to four
weeks because you're epithal cells are particularly good at regenerating themselves.

Speaker 3 (21:04):
That's right, And that is well, I guess that would
fall on the low side, obviously, if we're talking seven
to ten years. On the super low side, you have
the cells that line like you're intestine in your gut,
and those things don't last long at all because it's
such a harsh environment. You know, you wouldn't expect them
to last like weeks and months and years.

Speaker 1 (21:26):
I think, how long is it? Five days?

Speaker 2 (21:28):
Yeah, that's nothing but the.

Speaker 1 (21:29):
Structure of your guts that are beneath that membrane lining
that turns over five days. They last about fifteen years.

Speaker 3 (21:39):
Yeah, it's such a like a beautiful, elegant system. Yeah,
that we have right to keep us alive. Red blood
cells last about one hundred and twenty days. But then
you have things like cells in your bone which actually
regenerate as well, so your bones are over time, over
a much longer period of time, actually becoming I mean,

(22:01):
I hate to call them new bones, but they kind
of are, you know.

Speaker 1 (22:06):
Well, yeah, I mean compare if you took your femur
and somehow compared it to your femur when you were
fifteen years old, Like, they are two totally different bones.
Even though they're your bones. They were in the same place,
growing in the same person with the same DNA. There's
still different bones because they're made of different cells. Ten

(22:27):
years or so for the bones, yeah, something like that.
For the human skeleton, three hundred to five hundred days.
For the liver, very important organ it is. And one
of the other cool things about the liver is it's
just gangbusters that regenerating itself. You can apparently cut out
ninety five percent of a person's liver, and it will
grow back, and you won't have full function, but it

(22:49):
will function, and you'll survive with just five percent of
your liver.

Speaker 2 (22:54):
It's pretty amazing, actually.

Speaker 1 (22:56):
Yeah, because it will just grow right back, kind of
like a hornet's nest.

Speaker 3 (23:01):
Interestingly, the inner lens cells of your eye form and
your embryo and basically don't change. Yeah, now, is that
why you have suffered from degeneration and vision?

Speaker 1 (23:14):
That's what I would guess.

Speaker 2 (23:15):
Is that the reason?

Speaker 1 (23:16):
Yes, so the reason so with the corneal lens, Chuck.
When you're when you're born, when you're conceived, right, you
are a cell of coross that divides. Finally, once that
first division takes place, those corneal cells, they're set in stone.
Like your corneal cells are as old as you are,
same age as you. Other cells that make up different

(23:39):
parts of the eyes they're far newer. But your corneal cells,
your cerebral cortex cells, they think.

Speaker 3 (23:46):
Yeah, that's the one I mentioned. The brain and the
heart muscles, those are the two big ones. Because obviously
the reason we have diseases like Alzheimer's and dementia are
because the cerebral cortex has long a thought to not
regenerate cells at all.

Speaker 1 (24:02):
Yeah.

Speaker 3 (24:03):
Now I think they believe that they do in a
very small number.

Speaker 1 (24:10):
Or different reasons, like the old factory bulb supposedly does. Yeah,
in the hippocampus, so we can learn new things. Their
sense of smell can be refined over time.

Speaker 3 (24:19):
Yeah, And I think isn't that also the reason the
smell is very much tied to your memory, probably like
a smell can conjure up a memory more clearly. Yeah,
but the cerebral quartets itself, they don't think.

Speaker 2 (24:35):
Who was her name?

Speaker 3 (24:36):
Elizabeth Gould of Princeton did a lot of work on
this because it was just basically set in stone for
years like, no, it doesn't happen. And she did a
lot of work over the years trying to prove that
it did using tracer studies. And I think that where
they are now as they think it does.

Speaker 1 (24:54):
Some yeah here there, here there.

Speaker 3 (24:57):
But obviously we still have to mention Alzheimer, so it's
not it doesn't regenerate like the rest of the body,
not even close.

Speaker 1 (25:02):
Yeah. Alzheimer's also maybe produced I guess by plaques and
member plaque build up in between your neurons that keep
them from firing as well.

Speaker 3 (25:11):
Yeah, that's it seems like we're so close to figuring
out the secret, you know. Yeah, to uh, I don't
know about not dying ever. I'm not talking immortality, but
living much longer lives.

Speaker 1 (25:26):
Well, let's talk about that because all of this stuff
kind of leads to that question, if we regenerate so often,
why do we die? And we'll address that right after this.

(25:56):
All right, So, Chuck, there's this kind of there's this
idea that if we are regenerating ourselves every seven to
ten years, we're like the vast majority of our body
cells regenerate, why do we age and why do we die?
It doesn't it doesn't really make sense in that respect.

Speaker 3 (26:15):
Yeah, it's what they think is it has to do
with your DNA actually in the cell. Our cells as
we age, even the new ones that get replaced, which
really stinks, Yeah, become what they call cinicent, which means
that they can't divide any longer. We've talked about the
Hayflick limit before, or replicative centizence is basically how many

(26:38):
times your cells can divide over its lifetime. Yeah, and
I think like a fibroblast, which is the cells of
the connective tissue in mammals, it's about fifty cell divisions. Yeah,
and then it hits that point of centicence and it
starts sending out repair signals to your body that aren't necessary,
and that causes inflammation.

Speaker 2 (26:59):
And we've talked about inflammation kind of being the.

Speaker 3 (27:01):
Source of most most of the original problems that will
eventually lead to your death.

Speaker 2 (27:08):
Yeah, you know.

Speaker 3 (27:09):
Yeah, something becomes inflamed and leads to all kinds of problems.
There's no repair needed, so it's a false signal. So
they're trying to come up with drugs. Now, there's one
called wrap a micene that tries to stop the cells
from sending out those false signals, which is amazing.

Speaker 1 (27:27):
Yeah, that would be wonderful.

Speaker 2 (27:29):
You know.

Speaker 1 (27:30):
There's another explanation for it as well as that when
our cells divide, especially over time as we age, they're
basically making photocopies of themselves. Yeah, and you ultimately, years
down the road, end up making photocopies of photocopies, right,
and those don't tend to pan out very well. So

(27:51):
as far as analogies go, that one kind of makes
sense that, yes, we have brand new cells, but the
DNA copies, the DNA blueprints that they're based on it
have seen better days. Yeah, many years back, you know.

Speaker 2 (28:05):
Yeah, that makes sense. That's a good way to say it.
We also talked a little bit about whether or not
the heart muscle itself.

Speaker 3 (28:14):
Replenishes itself in the cells, and for a long time
they had no idea. But now thanks to our buddy
doctor Frisson, his pretty much. I don't even think we
said what his who he works with?

Speaker 2 (28:28):
Did we?

Speaker 1 (28:30):
No?

Speaker 2 (28:31):
He works with the with a K. Karolinska team.

Speaker 3 (28:34):
Oh yeah, just like incredible scientists that are making like
amazing advancements and trying to figure the stuff out. But
they did, in fact find that the heart does replace
itself the muscle cells. About one percent of the heart
muscles were replaced every year at age twenty five, and
that falls over your lifetime to less than half a
percent per year by the age seventy five.

Speaker 1 (28:54):
I spoke too soon. That does make sense.

Speaker 3 (28:56):
Yeah, So what they basically said is about half of
your heart's muscle.

Speaker 2 (29:00):
Cells will be exchanged during a normal lifetime.

Speaker 1 (29:04):
Okay, which is okay, it is, but as it's slowing
down over time, I mean the heart's kind of essential.

Speaker 3 (29:10):
Yeah, but they're hoping again to develop drugs that can
accelerate that process too. Yeah, And I don't know how
far along they are on that.

Speaker 2 (29:17):
But that'd be amazing.

Speaker 1 (29:20):
So there's this whole thing that kind of came up
to me man like that I don't all of this
raises this question to me, right, Yeah, if you look
at like you or me or any living things as
an investment, like a molecular investment in the ability to reproduce, right, Okay,

(29:42):
once you finish your reproductive age, then it does make
sense that you would just kind of there would be
built in this mechanism of aging and then death and
then decay, which is what we do. Yeah, we return
back to the earth. To put it in kind of
biblical terms, there's like that whole ashes to ashes, dust

(30:02):
to dust thing. Sure, it is very very true. And
if you look at us, and you look at all
living things as something that exchanges molecules with the external environment,
takes them in, puts them out right, and you look
at us as all connected in that sense, like we're

(30:24):
just like a plant exactly, or we're just like a rock,
like we're all that stuff, and those things are us
because we're able to exchange basic ingredients. Then it makes
total sense that a person would come together, be conceived,
start dividing as cells, you know, make more of itself,
and then start to age and then die and decay,

(30:47):
and then it would give something else a chance to
come up from that again. Right, sure, but then it
makes you it makes you wonder, what's the point of that?

Speaker 2 (30:55):
What do you mean?

Speaker 1 (30:56):
Like, think about it. If we're just the same as plants, Like.

Speaker 2 (30:59):
Why are we all here? Yeah?

Speaker 1 (31:00):
Like, if we're if the whole point is to just
basically recycle materials, because we are just recycling stuff from
the environment, and we're recycled as we die and decay,
what is the point? Is our point just to be
part of the carbon cycle, So we're moving carbon in
and out of ourselves, in and out of the environment,
moving it around. Or I don't understand what the point

(31:24):
is of life? I guess is what I'm saying here
in nihilis No, I'm not saying I don't believe that
there isn't a point. I'm just curious what it is,
because it because if we are the same as any
other living thing, and the definition of living is an
exchange with an active exchange with the surrounding environment. They're

(31:44):
breathing through, eating whatever. Yes. Then and then if you
kind of take that a little further and say, well,
clearly we're meant to like reproduce or something like that,
and then after that we age and die, what's the point?
Like why not just have one species of living thing? Yeah,

(32:05):
and just let that do all of your carbon recycling
or whatever.

Speaker 2 (32:09):
Yeah, I think are you about to quit the show?

Speaker 1 (32:14):
Yeah?

Speaker 2 (32:15):
I see what you mean.

Speaker 3 (32:15):
Like, if we look at ourselves as a purely mechanical
serving a purely mechanical function right on the planet.

Speaker 1 (32:23):
Like we are to the carbon cycle, what say, evaporation
is to the rain cycle, Like we're a means of
moving something along.

Speaker 3 (32:32):
Well, I think that's when you, man, this is getting philosophical.
I think that's when you start getting into questions of
the soul.

Speaker 1 (32:39):
Well, yeah, I mean it kind of makes you wonder like, well,
why would there be more than one species? It will
be much more efficient to just have one, maybe two.
There's all these different ones, so why.

Speaker 2 (32:49):
Yeah.

Speaker 1 (32:50):
The fact that that why is just sitting there and
flashing neon lights definitely made me wonder basically the opposite.
It's made me think in a different direction and then nihilistically.

Speaker 3 (33:02):
Like, we're only here for so long, and so if
there is the point is to like make the most
of your time.

Speaker 1 (33:08):
Well, I think that's a separate that's a separate part
of it. Yeah, because no matter what conclusion you come to,
whether Nope, we're just a means of recycling carbon and
that is it. Yeah, kind of like a Gaia theory
view of things. Or if you say no, like the
fact that we're inefficient and redundant as far as that

(33:29):
carbon recycling thing goes, suggests that maybe there is a
higher purpose to us. Either way, I feel like you
come to the conclusion or you should come to the
conclusion that the one thing we do know is that
we are here right now, and the best thing we
can do is make the absolute best of it for
ourselves and for other people as well.

Speaker 3 (33:49):
Yeah, and there are probably others out there that think
the whole point is to make as much cash as
you can, sure you can buy products.

Speaker 2 (33:55):
Yeah, Edward Burnez would.

Speaker 3 (33:57):
Probably say that, Yes he would, and he lived that
way in Man, that's interesting. I think we should I'd
love to tackle something philosophical and deep.

Speaker 1 (34:06):
Like the soul meaning of life.

Speaker 2 (34:08):
Yeah, that'd be tough.

Speaker 3 (34:09):
I mean that'd be cool, though, it would be cool.
We don't delve into that very much.

Speaker 1 (34:12):
No, we should. I'd like to do that. And consciousness
that's a really interesting one too, Like it doesn't make
any sense.

Speaker 3 (34:20):
It's a very trippy way forward for this show. Yeah,
we're gonna start getting weird.

Speaker 1 (34:23):
I took a lot of acid this morning. So, oh
that's great if you want to know more about some
just weird trippy stuff. How stuff works has a surprising
amount of it on there. I don't know. Just try
typing the word trippy into the search bar. You can
also type does your body really replace itself? Every seven years?

(34:44):
And it'll bring up this cool article. And I think
I said search bar at some point in time. So
how about some listener mail?

Speaker 2 (34:53):
I like how you specified you took a lot of.

Speaker 1 (34:55):
Acid just a little yeah, a lot fun of it?

Speaker 3 (35:00):
All right, I'm gonna call this multiple We got like
a bunch of emails in one day about people picking
at our grammar and things. Oh yeah, so I'm just
decided to read three of them because they're short. Hey, guys,
I generally enjoy the episodes, but you do have one
issue with your grammar and noun verb agreement. You tend

(35:21):
to say there are many lines of evidence or there's
lots of experiment showing instead of there are not there
is when the pronoun refers to a little subject. Check
yourselves next time.

Speaker 2 (35:33):
Guys. You typically make the mistake about ten times every show.

Speaker 1 (35:37):
Why don't you go recycle some carbon power?

Speaker 2 (35:40):
That's from Kim Keller in Temple Tariffs, Florida.

Speaker 1 (35:43):
Thanks.

Speaker 3 (35:45):
I always like to pick apart their emails too, about
because people usually make a mistake or two in their
own emails.

Speaker 2 (35:52):
Hey, guys, this one's from Blair. I love the show.
I hate to be nitpicky.

Speaker 1 (35:56):
They always say that, don't yeah right.

Speaker 3 (35:58):
Before they nitpick, But I have a grammar direction. It's
been bugging me for months, and Stonehinge was a major offender.
At least one of you not naming names frequently used
the word further when you really mean farther. The latter
term is used for literal distances. Further is only supposed
to be used figuratively.

Speaker 1 (36:16):
Huh.

Speaker 2 (36:17):
I didn't know that, Okay, so thanks Blair.

Speaker 3 (36:19):
Yeah, and then the last one, Phil who was an
English and grammar pronunciation freak. He says, hey, guys, when
there's an Italian word, you take your time to pronounce
it properly. The same with Japanese in the Far East
in general. So why don't you extend that same courtesy
to English.

Speaker 1 (36:34):
Words because we're masters of the language.

Speaker 3 (36:36):
And I mean words actually in the UK vernacular, not
American English. Salisbury, No, it's Salisbury, the Marlborough Downs, Nope,
marl bro Downs.

Speaker 1 (36:49):
Well, we're using the American vernacular because we're in America
and recording as American.

Speaker 2 (36:55):
That's from Phil.

Speaker 1 (36:57):
I had I addressed all those I think.

Speaker 2 (36:59):
Yeah, I think so. I feel good about it.

Speaker 1 (37:01):
I think it's good and very big of you two
have read those as listener mail. Why not nice job.

Speaker 3 (37:06):
Man, Yeah, we just we don't profess to talk gooder
than other people. We just do our little thing here
in the studio, send it out into the world nice
for people to pick apart.

Speaker 1 (37:17):
What we're doing is we're creating grammatical tableaus like that
Highlights magazine where it's like pick out the things that
don't belong. Yeah, that's what we're doing for you, guys.

Speaker 3 (37:27):
Yeah, keep you entertaining if you didn't have something to
complain about it, it'd be so boring.

Speaker 1 (37:30):
Yeah, if you want to nitpick or compliment or suggest
something whatever. If you want to get in touch with
us for any reason, you can do that by tweeting
to sysk Podcasts. You can join us on Facebook dot com,
slash Stuff you Should Know. You can send us an
email to stuff podcast at house stuffworks dot com, and
as always, joined us at our homeown the web, stuff

(37:51):
youshould Know dot com. Stuff you Should Know is a
production of iHeartRadio.

Speaker 3 (37:58):
For more podcasts my heart Radio, visit the iHeartRadio app,
Apple Podcasts, or wherever you listen to your favorite shows,