[tomp]

> wouldn't we have generally evolved not to eat things that killed us

I'm not convinced that's true, evolution only works to improve fertility; e.g. women after menopause have no evolutionary purpose. Even for men it's not clear why a longer life-span would result in increased reproductive success (maybe men have most/best children when they're young?).

Although I must admit it's surprising that there wasn't more evolutionary pressure to increase the "health-span" of people (i.e. women's fertile years, and men's and women's "peak physical performance" years) - maybe having too many children isn't a good thing (decreases genetic diversity pool and is thus bad for the whole species), or there was another kind of evolutionary trade-off (e.g. human females "waste" eggs by having a "concealed" ovulation every month, instead of being "in heat" (like in dogs) or by ovulating only after sex (like in cats); however, this allows for other evolutionarily beneficial adaptations [1]).

[1] https://en.wikipedia.org/wiki/Concealed_ovulation

[bluGill]

A long lifespan for men results in more reproductive success. Even one offspring from an old man is a success that the man who dies young doesn't have. This is a small factor but small can be enough.

There is also the factor that old people without children can help find food and defend the whole tribe thus ensuring better survival of their grandchildren.