Prisoner's Delemma

John K Clark (
Mon, 30 Jun 1997 21:19:43 -0700 (PDT)


On Sun, 29 Jun 1997 "Michael M. Butler" <butler@comp*> Wrote:

>a single Prisoner's Dilemma is a pretty threadbare situation. The
>_Evolution of Cooperation_ model assumes an _iterated_ Prisoner's
>Dilemma, for starters.

Well, what can I say except.., you're right. I believe the iterated Prisoner's
Dilemma is one of the most complex situations conceivable, so no matter what I
say about it I'm opening myself up to the charge of gross oversimplification.
If everybody adopted a tit-for-tat strategy most people and the world in
general would be better off, however a mutant that always defected would do
better than anybody else in such a population. A defector would produce more
descendants, until a sizable fraction of the population were defectors, and
then they would be worse off than their honest contemporaries and their
numbers decline. If things were simple and tit-for-tat was always the best
strategy then by now, after 4 billion years of Evolution, everybody would be
genetically determined to be scrupulously honest.
That has not been my experience.

>the consequences have to matter

or there is no point in talking about it.

>you have to be able to identify your counterpart,

You have to know your in the game, that your counterpart exists, but you
don't have to identify him.

>and rough parity has to exist

I'm not sure what you mean by this but I'll add one, your counterpart can't
be too clever. If your opponent's strategy is too complex it will look random
to you and you won't be able to play along. One good thing about tit-for-tat
is that it's simple.

>you have to be able to not tell if this is the last time you'll ever
>encounter the other party

True. I don't have a very high opinion of US Senators but they almost always
keep their promises, those made to other Senators that is. Having a reputation
for honesty among fellow Senators is to your advantage so you work at it,
developing such a reputation with Mr. Joe Average would be no great benefit
so the hell with it.

In the First World War the same solders sometimes fought each other from
their trenches for months at a time, they started to get polite, no artillery
attacks at dinner time or when bathing, they let the wounded be evacuated and
the mail truck get through. The Generals thought things were getting a
little too comfy so they started to rotate the troops around more often and
the cooperation ended.

John K Clark

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