[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.