[ryeights]

I think it is obvious at this point that the human body is designed to self-destruct, causing death at old age, once a certain biological threshold is reached. Resistance to this idea comes not from a rational perspective, but a semi-religious belief that your own body would not betray you.

[Tenoke]

It's odd to claim that's obvious when there are alternative explanations - the body is simply not all that optimized for old age because it isn't as much of a priority for passing genes and if such a complex system isn't optimized for it things are bound to give out.

[resoluteteeth]

The programmed aging theory may be "obvious" but there is not really evidence to support it as of the present.

If true, it would likely be very easy to stop aging (there would likely be some mechanism in cells causing aging that could simply be switched off), but this has not been borne out by research so far, and this is despite the fact that much anti-aging researching assumes it to be true.

The preponderance of the evidence currently seems to support the theory that aging is caused by damage building up over a lifetime.

[ryeights]

I don’t think it is at all necessarily true that there would be one mechanism for programmed aging that could be disabled by modern medicine. Rather, evolutionary pressures might cause many mechanisms to develop simultaneously to prevent aging of individuals too far beyond the point of reproductive viability.

If aging is caused by built-up damage, how would babies ever come to exist and live normal lifespans? The cell lines that produce new human embryos are millions of years old, yet each newly born human doesn’t face the problems of old age until they are 40+ years old.

[harshreality]

There's a strong filtering process. You're ignoring all the people, fetuses, embryos, and gametes that never pass on their genes.

When genomic damage gets too significant, and damage occurs to critical genes, individuals do not survive to reproductive age, fetuses are miscarried and aren't born, or embryonic development breaks and it might not even be known that fertilization occurred.

Aren't there also mechanisms that reduce accumulation of genetic damage in gametes compared to the rest of the body? That helps too.

[majormajor]

I don't understand the proposed mechanism of evolutionary pressure here.

Evolutionary pressure can result in traits being selected over others because the individuals with the un-selected traits frequently fail to pass them on. But the cause and effect isn't so much "we need to survive this, let's devise an adaptation," it's "a certain trait happened to end up providing an advantage." There isn't an intentional aspect to the randomness of genetics.

Why and how would evolution - random mutation and selection pressures - penalize the long-lived? Many past cultures actually did the opposite, and elevated and respected elders, for their roles as knowledge holders and such. So how would being longer lived cause your progeny - who at that point would already be born - to be less prolific?

[xenadu02]

If groups with many longer lived members suffered a disadvantage then natural selection would favor dying earlier, but not too early. You have to think about survival of genes in groups, not just individual survival.

FWIW my guess is it just didn't matter much. Surviving to 50 was plenty enough to have offspring yet not so long you compete with you grandkids for resources or become too much of a burden. That's already much much longer than most species so if anything evolution has already optimized humans to live fairly long lives. Once that got to be "long enough" there just wasn't enough selective pressure to matter.

[zarzavat]

That's two different kinds of damage.

The human genome is clearly extremely well preserved and is has not changed all that much in hundreds of thousands of years.

However for an individual human, damage to tissues occurs.

For example, if you lose a tooth, it is not going to grow back even though you still have "tooth genes". And this damage is happening to every system of the body e.g. pretty much everybody has atherosclerosis and eventually all humans will die from it if they live long enough.

To increase human lifespan we have to fix all of this entropic damage, which is not impossible but requires advances in medical technology, such as growing new tissue to replace damaged tissue.

[robbedpeter]

One end of the spectrum of reasonable possibilities is that evolution selected for genes that cause and or favor death the older an organism gets, through implicit mechanisms like lack of regenerative capacity, such as heart tissue, or explicit mechanisms, of which I'm not aware of any. Are there any genes that explicitly produce a timing mechanism, and thereby create a built-in notion of aging?

To my knowledge, it's all implicit, resulting from wear and tear, the gradual degradation of DNA because of the nature of chemistry on the surface of the planet, and not because any gene or biological mechanism moves an organism through some programmatic notion of mortality.

This seems true to the extent that given molecular level control of an organism, current knowledge would be sufficient to maintain lifespan to an arbitrary degree. Barring sci-fi nanotechnology, genetics and anti-aging have to figure out more robust repair and damage prevention to extend lifespan.

[cantrevealname]

> Are there any genes that explicitly produce a timing mechanism, and thereby create a built-in notion of aging?

Yes, telomeres.

Telomeres set a count on how many times a cell can divide before it ceases to divide and becoming old and useless; in humans, the count is 40-60 divisions and then the cell essentially dies.

There may be other timing mechanisms that haven't been discovered as well.

[outworlder]

It's less of a timing and more like of a "TTL" of a network packet. If you don't divide you don't use them up, even if you could live a thousand years. If you keep dividing like crazy, it will eventually reach useful DNA and the cell will die.

They seem to be quite specifically an anti-cancer measure.

[m463]

I've wondered what kinds of things we're doing both good and bad to our bodies.

For example, with modern society food availability is high. For example we could eat kale every day. Starving is optional. yet I've read that fasting is the way to metabolize senescent cells, but maybe nobody does it anymore.

[twobitshifter]

I wouldn’t say self destruct, your body and your child’s body and your grandchild’s body are all a continuation of the same organism. Selection favors clearing out the old dead mutated cells and that is just extending to bodies as well. If we conceptualize ourselves as separate from our descendents, we think we’re dying, but if we procreate our cell line lives on, which is the only outcome which matters to evolution.

[ryeights]

That is exactly the theory.

As an individual it honestly doesn’t matter that much to me if my cell line continues on. I will still be dead.

[outworlder]

There's little incentive for the repair processes to be perfect. There would actually be zero incentive after we reproduce - and some species are exactly like that. The moment you reproduce, you die.

Humans, being a social species, might have pushed evolution towards trying to repair a bit more than it should. Older humans can still contribute - sometimes a lot - to the group. Older males can still reproduce in many cases.

[antattack]

Evolution's natural selection looses it's power after ones child reached maturity. It's now up to our frontal lobe to keep on improving our bodies.

With that said, it's possible that long life might have negative effect on resource availability which might affect procreation and child rearing, and might find shorter life-span more advantageous to survival of species.

[Rury]

>belief that your own body would not betray you

I think this is a fair point. We're multicellular life forms. We're not 1 living thing, but rather a collection of many living things working together. It could be that some of those living things start to betray each other (for personal gain) which aids in our demise. Just as individual humans can do the same to each other, leading to society's demise. But I'm not sure that means we were designed to self-destruct.

[cheschire]

Why is that “obvious” and why is the “other” side the religious one and not your “design” assertion?

I’m not an expert on such subjects but it seems more closely related to the concepts of evolution to say natural selection does not show preference for abnormally long lived individuals because it is unknown or unimportant at time of procreation which traits lead towards lifetime longevity beyond short term hunter gatherer traits.

[ryeights]

Under the traditional view, the most evolutionarily advantageous individual is one that lives forever and continues to spread their genes indefinitely, producing hundreds of offspring. Why is this not what we see in practice?

[Rury]

I think it's because, we would live forever, but something goes awry after being mature for so long that our bodies haven't evolved far enough to counteract yet. We solve this by sexually reproducing, which resets the clock on age, so our cell line is still able to live on. We do this instead of resetting our mature bodies because reseting 1 or few cells is easier than resetting/replacing billions that are dysfunctional. So we sorta evolved on the path of least resistance required to live forever, and require further evolution before our mature bodies can do the same, so to speak.

[jstanley]

There's no advantage to having a single individual who lives and reproduces forever compared to having his offspring, and his offspring's offspring, etc. reproduce forever.

[gscott]

I plan to go to China every 15 years and get all new organs. As long as I don't accidentally turn on Tesla Auto-Pilot I should live a long time.

[threatripper]

> body is designed to self-destruct

This way of thinking is dangerous. This is like saying that there is "planned obsolescence" when in reality products are designed to last a certain period. They are not designed to fail after that period but they are also not designed to last longer than that period. The end result is similar but the intention is totally different.

[judge2020]

Perhaps it is designed to self-destruct, but we're pretty good at making up for deficiencies in our weakest links: https://www.statista.com/statistics/1040079/life-expectancy-...

[strictfp]

It's hard to survive in the presence of a constant onslaught of forces trying to break you down. Plus we have another way of surviving: multiplying. And multiplying gives us mutations as well, i.e better fitness. So why should our organism optimize for longlivety?