[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.