At the excellent Marginal Revolution blog, economist Tyler Cowen takes on a thought experiment: What if we all died at forty? An excerpt from his answer:

“One question is how child-bearing norms will evolve.  There will be considerable pressure to have kids at age eighteen or so.  (It might be considered unethical to have a child at age thirty-five, although if the fertility rate falls enough the economy might shift heavily into orphanages and this could be considered virtuous nonetheless.) I predict many people would become much stricter in their morals and more religious, and they will have children quite early.

Other people would attempt to maintain a collegiate lifestyle through their death at age forty.  There would be a polarization of outcomes and approaches to life.  Old age as an equalizer, and as an enforcer of responsible savings behavior, would be gone.

The likelihood of warfare would rise, if only because the sage elderly won’t be around and male hormones will run rampant.” (Thanks Browser.)