Since you started reading, over a million of your cells have died. It’s natural, don’t worry. But you’re literally covered in dead stuff. Your fingernails, your hair, the outermost layer of your skin, everything is made of dead cells. And you constantly lose this stuff. Each week, about 5.5 and a half grams of dead skin peels off your body. 80% of the dust is dead human skin. Why don’t we all have cancer, then?
But for the most part you are made of living stuff. You are a biological furnace, burning the energy of food to move, breathe, think and stay warm. Your cells are busy and active, dividing millions and millions of times a day. But here’s the really shocking thing about the cell division process, the replication of instructions. The DNA for each daughter cell it requires a copy of an exact sequence of three billion nucleotides. Several. Thankfully, our bodies are perfectly adapted to do this, but they aren’t perfect. Every time a single cell in your body divides, the enzymes that synthesize your DNA make 120,000 mistakes. Some of these mistakes end up being beneficial, others harmful and others just plain neutral, they make no difference.
Why don’t we all have cancer?
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 its own blood supply, potentially multiply by always and moving away from where it started to spread throughout the body, it becomes a special type of cell. We found 200 diseases with various origins and natures that fit this description. Although they are different, they are often called by the same name: cancer.
DNA mutations occur randomly in your body, but they can also be inherited or caused byambient. For example, exposure to ultraviolet radiation from the sun can cause all sorts 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. Environmental damage to the body, whether carcinogenic or not, is a serious problem.
Given the large number of environmental dangers to our DNA and the number of mistakes our body makes every day with our DNA, it is amazing that we all don’t develop cancer constantly and soon after birth. One of the things we have to thank is the self-correction of our body. Biological mechanisms, such as error correction, capture and correct or stop more than 99% of DNA replication errors. We age and die for many, many reasons. But when it comes to cancers, our body’s internal self-correction is like self-correction on your phone. It’s good enough, but it’s not perfect.
The selection shadow
Tumors still develop, especially after the accumulation of errors and mutations over time. After all, natural selection cannot see much, due to a phenomenon called selection shadow. We are not all the same, and if your genetic variations make you and your children more successful in breeding, your characteristics become more common.
We found evidence of the selection shade at work with mice and bats. Raised in perfect conditions, with medicines and safe lives, mice only live two or three years. While bats, of similar size and metabolism, can live for thirty years or more. The significant difference is that, unlike mice, bats have had fewer predators in the wild for millions of years. That is, a lower chance of dying early due to extrinsic mortality. On average, they had more days of time for natural selection. This could be an excellent explanation of why the diseases affecting our multicellular complexes in old age are still with us. Why don’t we all have cancer?
Good news for the future
Science is making progress against delayed-acting diseases. And when it comes to cancer, 40 years ago only one in four people lived ten years or more after being diagnosed. Today this number is 2 out of 4. And in just twenty years this statistic could rise to 3 out of 4. Every day we learn more. The process is slow but steady. Because cancer is not just one. It is unlikely that there will ever be a single cure for cancer because there are two hundred different types. But there will be better treatments and methods for prevention and diagnosis. Progress comes from everywhere. Natural selection has already done some work, now it’s our turn.
(We remind you to carefully read the warnings in this regard, which can be consulted who”)
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