Previously in series:  Why Our Kind Can't Cooperate

In the Ultimatum Game, the first player chooses how to split $10 between themselves and the second player, and the second player decides whether to accept the split or reject it—in the latter case, both parties get nothing.  So far as conventional causal decision theory goes (two-box on Newcomb's Problem, defect in Prisoner's Dilemma), the second player should prefer any non-zero amount to nothing.  But if the first player expects this behavior—accept any non-zero offer—then they have no motive to offer more than a penny.  As I assume you all know by now, I am no fan of conventional causal decision theory.  Those of us who remain interested in cooperating on the Prisoner's Dilemma, either because it's iterated, or because we have a term in our utility function for fairness, or because we use an unconventional decision theory, may also not accept an offer of one penny.

And in fact, most Ultimatum "deciders" offer an even split; and most Ultimatum "accepters" reject any offer less than 20%.  A 100 USD game played in Indonesia (average per capita income at the time: 670 USD) showed offers of 30 USD being turned down, although this equates to two week's wages.  We can probably also assume that the players in Indonesia were not thinking about the academic debate over Newcomblike problems—this is just the way people feel about Ultimatum Games, even ones played for real money.

There's an analogue of the Ultimatum Game in group coordination.  (Has it been studied?  I'd hope so...)  Let's say there's a common project—in fact, let's say that it's an altruistic common project, aimed at helping mugging victims in Canada, or something.  If you join this group project, you'll get more done than you could on your own, relative to your utility function.  So, obviously, you should join.

But wait!  The anti-mugging project keeps their funds invested in a money market fund!  That's ridiculous; it won't earn even as much interest as US Treasuries, let alone a dividend-paying index fund.

Clearly, this project is run by morons, and you shouldn't join until they change their malinvesting ways.

Now you might realize—if you stopped to think about it—that all things considered, you would still do better by working with the common anti-mugging project, than striking out on your own to fight crime.  But then—you might perhaps also realize—if you too easily assent to joining the group, why, what motive would they have to change their malinvesting ways?

Well...  Okay, look.  Possibly because we're out of the ancestral environment where everyone knows everyone else... and possibly because the nonconformist crowd tries to repudiate normal group-cohering forces like conformity and leader-worship...

...It seems to me that people in the atheist/libertarian/technophile/sf-fan/etcetera cluster often set their joining prices way way way too high.  Like a 50-way split Ultimatum game, where every one of 50 players demands at least 20% of the money.