Akka emails me:

I think one of the things that make planning (and living) life so hard is the combination of the facts that Its end date is uncertain It is rather highly likely that one’s faculties will be duller towards the end. If it was certain that when we sleep on our 40th birthday, we wouldn’t wake up, how different would the world be? Economically? Culturally? Will it be more peaceful? More left leaning?

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.

Credit would be harder to come by and the rate of home ownership would fall. The rate of voting turnout will go down, as would the degree of wealth inequality and the amount of innovation. Federal discretionary spending, as a percentage of the budget, would rise.

We can look at data from Huntington’s Disease, for instance see the Oster, Shoulson, and Dorsey paper. Only five to ten percent of potential carriers choose to learn whether they will have the disease, even though the cost of the test is low. That suggests knowledge of a finite horizon is itself costly and a source of discomfort. Those who learn they will encounter bad fates from the disease are more likely to divorce, more likely to get pregnant, and much more likely to report significant financial changes and changes in recreational activities. Of course these are solo individuals embedded in societies with normal life expectancies; if everyone were to meet an early untimely end I believe the (partial and polarized) shift toward conservative and religious norms would be much stronger.