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.
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.
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.
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?
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.
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.
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.
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.
They seem to be quite specifically an anti-cancer measure.
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.
As an individual it honestly doesn’t matter that much to me if my cell line continues on. I will still be dead.
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.
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.
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.
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.
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.