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Comment by bnegreve | Hacker News Reader

From what I understand, there's only a limited number of times you can perform cellular division without getting erroneous DNA copies (cancerous cells).

Like humans, elephants start their life with one cell, which is then replicated over and over again until the end of their lives. But somehow, elephants manage to reach body sizes 100 times bigger than humans (meaning many more cellular divisions) without having cancerous cells.

I think that's the basic observation that triggers this kind of research.

Disclaimer: I am no expert at all.

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Our gamete cells have been undergoing an unlimited number of cellular divisions since... well, since life started. What's so special about somatic cells that makes them cancerous after so many divisions?

> What's so special about somatic cells that makes them cancerous after so many divisions?

Nothing, actually. I'd rephrase the parent comment.

There is in fact a fixed (somewhat small) probability that replication ends up in a mutation. But looking at the continuous replication going on in our cells as a Bernoulli process, you can find a number N such that there is a probability of Q (say 99%) that a mutation happened before the Nth replication.

It's actually that they aren't special. With gametes the body cares about making sure things work out well, and you only need the one embryonic stem cell to be issue free (discarding any with mutations) to create a new healthy human. With the somatic cells though you just need one (oversimplifying massively here of course) cell to become cancerous to kill the person, and the DNA repair mechanisms become more likely to fail throughout life

In animals, the gamete cells are selected at an early time in the embryo, and the don't divide as much times as the other cells. (Most os the cells of the testicles / ovary are just normal cells that provide support for the germinal cells.) Reducing the number of divisions reduce the number of mutations between generations. https://en.wikipedia.org/wiki/Germ_cell

Also when a cell becomes cancerous it usually has a broken version of many of the checks to avoid uncontrolled division and to ensure that the cell cooperates with the neighbor cells. This will probably cause problems in the formation of the embryo or fetus. Or kill the baby before reproduction age. So cancerous germ cells are self eliminated from the gene pool.

Someone else basically said it but to put it more plainly: broken gametes produce no-fertilization, no-implantation, miscarriages, and non-viable or infertile offspring. So only the good ones get through.

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