Hey, Vsauce. Michael here.
Since this video began
more than a million of your cells have
died. It's natural, don't worry.
But you are literally covered with death
Dead stuff. Fingernails, your hair,
the outermost layer of your skin - all made out of dead things.
And you are losing this dead stuff constantly. Every week
about 5.5 grams of dead skin sheds off of your body.
Ohio State University found that 80%
of that material you see indoors, beautifully dancing across sunbeams,
is dead human skin.
But for the most part, you are made out of
living stuff. You are a biological
furnace, burning food energy to move and breathe and
think and stay warm. As you can see on Grand-Illusions[.com], the heat from your own
hand while you sit still
is enough to run a Stirling engine.
Your cells are busy and active and dividing
millions and millions of times every day. In fact, because of that, you shouldn't even
really be called a person.
You should be called a persON
and on and on and on and on and on and on and on... But here's the really
mind-blowing
thing about the mind sustaining process of cell division,
the replication of instructions. DNA for each daughter cell
requires copying an exact sequence
of three billion nucleotides. That's a lot.
Luckily, our bodies are perfect-ly happy to do it but they're not perfect.
Every time a single cell in your body divides, the enzymes that synthesize
your DNA
make 120,000 mistakes.
Some of these mistakes
wind up being beneficial. Some of these mistakes wind up being harmful and
some are just neutral,
they don't make a difference. But if a mistake,
a mutation in a cell's DNA, causes the cell to behave abnormally
and stimulate its own growth, ignore signals to stop,
stimulate the body to give it its own blood supply, potentially
multiply forever and unstick from where it began to spread throughout the body,
it becomes a special type of cell.
We have found 200 diseases with various origins and natures that
fit this description. Despite being different, they often go by the same name:
cancer.
DNA mutations occur randomly in your body
but they can also be inherited or caused by the environment.
For example, exposure to ultraviolet radiation from the Sun
can cause all kinds of damage, including genetic damage.
If little or no skin protection is used, the accumulation of all these types of damage
can be quite dramatic. This man drove a truck
for years, exposing one side of his face to more sunlight
than the other.
And for 15 years this woman worked in a room
that had the same window. A window to her left.
Environmental damage to the body,
whether cancer-causing or not, is serious business.
In fact, giraffes have black tongues because the dark pigmentation protects
their tongues
from solar radiation while they're hanging out all day.
Go back far enough, beyond where sunshine hits, and their tongues are pink.
Given the sheer number of environmental dangers to our DNA
and the sheer number of mistakes our own bodies make with our DNA every day,
it is incredible that we all aren't developing cancers constantly
and immediately after being born. One of the things we have to thank
is our body's own version of autocorrect.
Biological mechanisms, like proofreading and mismatch repair,
catch and correct or stop more than 99% of errors.
We grow old and pass away for many,
many reasons. But when it comes to cancers, our bodies'
own internal autocorrect is like the autocorrect
on your phone. It's pretty good, but it's not perfect. Cancers
still develop, especially after the accumulation of mistakes and mutations
over time. I'm incredibly grateful to Cancer Research UK.
They helped me a lot with this episode, and thanks to work by groups like them,
we are at an accelerating rate finding ways to prevent and control cancer
beyond what our bodies can do alone. I mean, after all, natural selection can
only see so much
because of the selection shadow.
We aren't all the same and if your genetic variations make you and your children
more successful at reproducing,
well, what do you know, your characteristics become more common.
But this phenomenon has a weak influence
here. Later in life, after your role in reproduction and raising offspring to
independence
has passed.
We have found evidence of the selection shadow
at work with mice and bats.
Raised under perfect conditions, with veterinary medicine and safe lives,
mice only live about two to three years.
Whereas bats, with similar sizes and metabolisms, can live for
thirty years or more. The significant difference here is that
unlike mice, bats have had in the wild for millions of years
fewer predators - a smaller chance of dying early
due to extrinsic mortality. They've, on average, had more days for natural selection
to influence. This could be a very good explanation for why diseases that affect
our complex multicellular selves
late in life are still with us.
But wait, why are humans living so long today?
I mean, in the past, but genetically recently, weren't
teenagers considered middle aged?
Not really. Well, it's true that in the past life expectancies were quite
a bit lower, a life expectancy is merely an
average number of years a person was expected to live as soon as they were born.
And in the past, infant mortality was so high
the average was brought down significantly. It's true that in the
early 1600s, here
in England, life expectancy was only 35 years.
But if you made the age of 21... Well,
you could easily expect to live well into your 60s.
Lifespans that go beyond the age of reproduction have
always made sense for humans, because we are intelligent
and social, useful to one another and our children
take a lot of time and guidance to gain independence.
But that just moves the selection shadow ahead. It's still there,
suggesting that, in the end, our bodies might just be
tools our sex cells use to reproduce
and grow up to do it again. Nature and time haven't helped our bodies battle
late acting diseases because a chicken
is just an egg's way of making another egg.
But maybe not for long. Our minds and modern science technology engineering
and mathematics are making progress
against late acting diseases. And when it comes to cancers,
Cancer Research UK points out that 40 years ago
only one in four people lived ten years or longer
after being diagnosed. Today that number is 2 in 4.
And they believe that in only twenty years that statistic could be as high as 3 in 4.
Refrigeration and sanitation are tackling stomach cancers caused by infection,
vaccines are preventing cervical cancer, anti-smoking campaigns and reductions
of obesity and diabetes and the elimination
of cancer-causing chemicals from our everyday lives are giving us an edge.
We learn more every single day. The process
is slow, but steady. Because cancer is not just
one thing. It's unlikely there will ever be a single cure for cancer because
there are two hundred different types
of cancers. But there will be cures and better methods of prevention
and detection. Advances are coming from all over.
For example, what we have learned about controlling proton beams because of the
Large Hadron Collider
has reduced the need for special shields during the removal of eye tumours.
The statistical surprise that cancers aren't more common in our bodies
is a sign that we're involved in a relay race.
Natural selection already did some of the work, now it's our turn.
When we talk about cancer we often use the language of war:
it's a battle, it's a fight. But the challenge
isn't so much a war with winners and losers and surrender
as it is a mutiny. We can't help the fact that we are all at sea.
Natural selection at least gave us boats
but now we are making where those boats go
our decision.
And as always,
thanks for watching.