more than a million of your cells have

died its 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 five and a half grams of dead skin sheds off of your body

Ohio State University found that eighty percent

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 breath and

think and stay warm. As you can see on Grand illusions 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 thousand 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 abnormal

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 nature's 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 tongs because the dark pigmentation protects

their tongues

from solar radiation while there 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 think

is our body's own version of autocorrect

biological mechanisms like proofreading and mismatch repair

catch and correct or stop more than 99 percent 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 vetinary 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 multi cellular 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 1600's here

in England life expectancy was only thirty-five years

but if you made the age of 21 well

you could easily expect to live well into your 60's

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 are sex cells used 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 eggs 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 its 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 at the

Large Hadron Collider

has reduced the need for special shields during the removal of eye tuners

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

its 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