[kiba]

I might not have the heart to but a rational agent acting in the interest of the entire population would. In fact this is basically what natural selection did to us. If much longer lifespans would have benefited our species we would already have them.

Natural selection doesn't act upon humans for the sake of humanity, nor did it ever asked what humans want or need.

It turns out that the way out brains crystallize as we age and make us better at teaching but worse at changing our minds means our ideal lifespan is not very different than the ones we have. I know individuals can work very hard to avoid this outcome but most people don't.

Citation? I would argue that adults are better at learning languages, because we have the benefit of hindsight, experience, and reasoning.

Whereas children are merely subjected to immerse learning environment from which to acquire languages pretty much every waking hours of their life.