Comment by YeGoblynQueenne | Hacker News Reader

Comment by YeGoblynQueenne | Hacker News Reader

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YeGoblynQueenne

>> After cancer no longer kills you, something else will.

Well, currently, unless something else kills you, cancer certainly will. Cancer is a biological inevitability, that can only be kept at bay for so long by the efforts of the human immune system. And as we all know, the longer we all live, the more of us will get cancer, because the transcription errors that eventually cause it become all the more likely as time goes by.

Bostrom seems to think -it's not expressed in so many words- that if we halt ageing, we'd also defeat cancer, somehow, perhaps by having an immune system that is forever as powerful as a young person's. The problem with this idea is that young people do get cancer, despite their healthy immune systems.

It looks like everyone alive has a probability to get cancer at some point in their life. For younger people this probability is relatively low, but currently, we only spend a few years of our lives (let's say 20) being young. If our "young" period is suddendly extended to 50 or 60 years, or more, the probabilty to get cancer while "young" in this sense, will increase. Imagine rolling a 100-sided die every year for 20 years, hoping not to roll a 01. Now imagine doing the same for 100 years. It's obvious that you're much more likely to roll at least one 01 in 100 years, than in 20.

So maybe Bostrom's magical health-extension pills won't work exactly like he thinks. Maybe we can all extend our life spans (well, those of us who can afford that mythical panacea) but not for as long as we'd like, and maybe we will find that if we extend our life for long enough, we will increase our likelihood to die of the most dreaded of diseases to an absolute certainty.

And wouldn't that really suck?

Whether cancer is special in this regard depends on what you mean by aging. I work in this area and consider it to mean "damage (maladaptive changes) that accumulate over time, first degrading function and ultimately leading to catastrophic failure" . This is not the only model but it is widespread.

So for something like the cardiovascular system, chronic stress, inflammation, ROS etc are the triggers, atherosclerosis and endothelial weakening is the damage, and stroke or heart attack is the failure. In the case of cancer, it is radiation or replication error, DNA mutation, and metastasis, respectively.

The key for "curing" aging would be the ability to reverse or repair damage (in this case, to selectively kill cells that are mutated or precancerous). To extend life it is sufficient to merely slow damage accumulation rate.

I don't claim to understand how all this stuff works, besides the part about modelling it as a probability (a Bernoulli process), but I wonder to what extent it is possible to slow the damage. For instance, if you're bleeding, you may be able to slow it - but if you don't stop it completely, eventually you will bleed to death.

I also wonder whether someone living for a very long time wouldn't eventually suffer irreparable damage because of the radiation from the environment accumulating in the tissues. Nobody's claiming that we can survive, say, being thrown into a volcano (an active one, I mean), just by being more healthy and young. There are clearly environmental hazards that the body cannot withstand, senescence or no senescence. It is very likely that such environmental hazards hitherto unforseen will begin to reveal themselves once our lives are extended enough and that we will eventually find out that there is a hard upper limit for the amount of time that these frail bodies can keep serving for.

I clarify that this is not something to celebrate, or even accept. Let us not go gentle in to that good night, by all means. On the other hand I think it is ridiculous to believe that in a universe where galaxies die, human beings can keep going like the Duracell bunny for as long as we like, thanks to Nick Bostrom's Amazing Rejuvenating Pills™.

> I wonder to what extent it is possible to slow the damage. For instance, if you're bleeding, you may be able to slow it - but if you don't stop it completely, eventually you will bleed to death.

Yes, exactly. Well, the simplistic model is that you have a rate of damage (RD) and rate of repair/replacement (RP), and if RD > RP, the system will eventually fall apart. "Repair" consists of both your body's endogeneous repair or replacement processes and exogeneous things we might do.

Most researchers focus on RD, because it seems easier for us to do things about that. Calorie restriction probably mostly affects RD instead of RP, for example. In high theory, one could stop aging purely by lowering RD enough so that it is below the body's endogeneous RR.

But in reality, it is easier for the body to detect and repair some kinds of damage than others. It is quite hard for the body to detect DNA mutation in a cell before it starts actively causing aberrant behavior in a cell, although such mechanisms exist.

> I think it is ridiculous to believe that in a universe where galaxies die, human beings can keep going like the Duracell bunny for as long as we like

Well, at THAT timescale, we are talking about problems of physics and thermodynamics, not biology. But if you consider that in some sense life on Earth has proceeded in an unbroken chain for ~4B years, you can see that it is possible to go quite far by decreasing local entropy at the expense, of course, of global entropy. I do not see how physics prevents human lifespan of at least 10K years, but the technical problems are immense, and I do not predict major success within our lifetimes.

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