[jennyp]

There's a slight problem with the senescence model and that is that past reproductive years, mortality drops off as age increases.

Really? It holds across many species? How exactly do you define "mortality" in this case?

[Nebullis]

How exactly do you define "mortality" in this case?

That's a good question. Mortality rates level off at older ages. The speed slows down. Mutations accumulate over a lifetime, but, apparently the expectation of mortality based on rates of deleterious effects, both from mutations and from active genes causing rapid senescence, slow down at some point far beyond reproductive age.