# Demographic Prisoner's Dilemma : a probabilistic framework

## TL;DR

This paper introduces a probabilistic framework for the Demographic Prisoner's Dilemma, analyzing conditions for cooperation survival or extinction, and establishes mean field models with eternal coexistence under certain payoff conditions.

## Contribution

It develops a novel probabilistic model for the Demographic Prisoner's Dilemma and proves conditions for cooperation extinction or eternal survival, including mean field approximations.

## Key findings

- Cooperators die out if Sucker payoff exceeds Reward significantly.
- Cooperators and defectors can coexist indefinitely under certain payoff conditions.
- Mean Field model shows potential for eternal cooperation under weaker assumptions.

## Abstract

We put a probabilistic framework on the Demographic Prisoner's Dilemma. In this model, cooperating and defecting individuals are placed on a torus to move and play prisoner's dilemma game, if they are on the same site. Each individual accumulates its payoff into a quantity called wealth. If an individual becomes wealthy enough, it can have an offspring. If its wealth becomes negative, it disappears. In this framework we prove that if if the Sucker payoff is far greater than the Reward then for all initial state almost surely all cooperators will die. Moreover if the Temptation payoff (resp. Reward) are far greater than the Punition (resp. Sucker payoff) then for all initial state with positive probability cooperators and defectors live \emph{ad vitam eternam}. We also set a Mean Field model on the demographic prisoner's dilemma and prove on a linearized version of the Mean Field model that with weaker assumptions with positive probability Cooperators live \emph{ad vitam eternam}.