Why Don't We All Have Cancer?

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 perfectly 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 that 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 tumors. 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.