In 1980, game theorist Robert Axelrod ran a famous Iterated Prisoner’s Dilemma Tournament.

He asked other game theorists to send in their best strategies in the form of “bots”, short pieces of code that took an opponent’s actions as input and returned one of the classic Prisoner’s Dilemma outputs of COOPERATE or DEFECT. For example, you might have a bot that COOPERATES a random 80% of the time, but DEFECTS against another bot that plays DEFECT more than 20% of the time, except on the last round, where it always DEFECTS, or if its opponent plays DEFECT in response to COOPERATE.

In the “tournament”, each bot “encountered” other bots at random for a hundred rounds of Prisoners’ Dilemma; after all the bots had finished their matches, the strategy with the highest total utility won.

To everyone’s surprise, the winner was a super-simple strategy called TIT-FOR-TAT:

https://readscottalexander.com/posts/acx-the-early-christian-strategy

The rise of Christianity is a great puzzle. In 40 AD, there were maybe a thousand Christians. Their Messiah had just been executed, and they were on the wrong side of an intercontinental empire that had crushed all previous foes. By 400, there were forty million, and they were set to dominate the next millennium of Western history.

Imagine taking a time machine to the year 2300 AD, and everyone is Scientologist. The United States is >99% Scientologist. So is Latin America and most of Europe. The Middle East follows some heretical pseudo-Scientology that thinks L Ron Hubbard was a great prophet, but maybe not the greatest prophet.

This can only begin to capture how surprised the early Imperial Romans would be to learn of the triumph of Christianity. At least Scientology has a lot of money and a cut-throat recruitment arm! At least they fight back when you persecute them! At least they seem to be in the game!

https://www.astralcodexten.com/p/book-review-the-rise-of-christianity

I.

Polymarket (and prediction markets in general) had an amazing Election Night. They called states impressively early and accurately, kept the site stable through what must have been incredible strain, and have successfully gotten prediction markets in front of the world (including the Trump campaign). From here it’s a flywheel; victory building on victory. Enough people heard of them this election that they’ll never lack for customers. And maybe Trump’s CFTC will be kinder than Biden’s and relax some of the constraints they’re operating under. They’ve realized the long-time rationalist dream of a widely-used prediction market with high volume, deserve more praise than I can give them here, and I couldn’t be happier with their progress.

But I also think their Trump shares were mispriced by about ten cents, and that Trump’s victory in the election doesn’t do much to vindicate their numbers.

https://www.astralcodexten.com/p/congrats-to-polymarket-but-i-still