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Comment by chubot | Hacker News Reader

Didn't early humans also rarely get cancer?

My understanding is that cancer is one of those things you die from if you don't die at child birth, get eaten by predators, or get the flu, polio, malaria, the plague, etc.

That is, the reason cancer is such a big deal in modern times is because other causes of death have been controlled.

I don't know much about elephants but I imagine cancer is still low on their list of things to worry about (humans are probably a lot higher up) If they started living a lot longer, it would probably show up more.

People under 40-50 also rarely get cancer. Although I'm sure the human environment has produced some more causes of it that make those rates higher than they used to be.

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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.

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.

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.

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

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.

We see cancer in the human fossil record.

https://www.cancer.org/cancer/cancer-basics/history-of-cance...

Prehistoric human lifetime is very hard to estimate, but I have heard reports that while infant mortality was high, actual lifetimes could still reach 70+ years

It's true that life expectancy used to be very low due to very high infant mortality, but even after that it wasn't easy going:

> Based on Neolithic and Bronze Age data, the total life expectancy at 15 would not exceed 34 years. Based on the data from modern hunter-gatherer populations, it is estimated that at 15, life expectancy was an additional 39 years (total 54), with a 0.60 probability of reaching 15.

https://en.wikipedia.org/wiki/Life_expectancy#Variation_over...

That's in the times when agriculture became a thing. It meant that people lived in a very crowded way where the limited tracts of very fertile land was, settled and with very poor sanitation. Infections were rampant, and famines in poor crop years, common. Hunter-gatherers had it much better - except there were a lot fewer of them.

I don't get this argument. Sure, some did reach old age but we are way more interested in what percentage of them it was

Assume half of babies die in childbirth or by age 3. Assume another half die before they reach 25. Even assume that another half die before age 60. That means there are still tribal elders that can pass on information and educate the small children they take care of while parents are out getting food. It's a huge deal for a species based on cultural learning.

> That means there are still tribal elders that can pass on information [...] It's a huge deal for a species based on cultural learning.

True, it might be easy to claim that there is no way to select for longevity because longevity happens after the birth of the offspring. Having elder generations around to improve the odds of survival for the descendants should make longevity a possible factor in selection.

FWIW, the human birth process is not viable without cultural accumulation. Baby heads are too damn big and kill women if they don't have a midwife to help them through. But it's a cycle and the midwife is only helpful herself because she has an oversized brain to pass along cultural knowledge.

Elephants have roughly as long a lifespan as humans and there are parts of the world where their populations thrive, even in the wild. I don't think dying young is a cause in this case.

Still, we have pediatric cancers that are not caused by lifestyle. I wonder what's the ratio for small elephants. Are the also more protected ?

But how often would those be encountered in an average city? Because that's about the size of the total elephant population and if a handful of individuals got a rare cancer, chances that biologists would learn of it are still slim.

I believe I've read this verbiage around cancer in pets, such as domestic cats living far longer than "intended".

Pet rats ("fancy rats") were largely separated fron the wild gene pool about 150 years ago. They can live to three years or more, and are quite prone to benign tumours.

(source: wife used to be a fancy-rat breeder)

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