>Our natural instincts are not to die after we reproduce.
Well of course not, since we might be reproduce more if we stay alive longer. And we do start to die around the time we start to lose fertility, which isn't an "instinct" to die, but clearly our bodies are not adapted to live longer.
You think we're not adapted to live longer because it takes us 60+ years to die after the only ~14 to become fertile? That seems like evidence of us being adapted to live longer. We are actually the longest-lived land mammal on the planet. So why on Earth would you conclude the opposite?
Besides: http://lesswrong.com/lw/l0/adaptationexecuters_not_fitnessma...
We execute the adaptations we already have, we do not optimize for evolutionary goals. We have no obligation to pay them any mind whatsoever.