Learned Cooperation: from Defection to Cooperation

This section is organized around your central motto:

The Nature and Nurture of Cooperation
Here we focus on the nurture side: how cooperation can emerge from learning.

Why start with defection?

Cooperation is non-trivial. In many strategic settings, selfish behavior is the local default. So the right starting point is:

• first explain why defection is often rational at first glance,
• then show when repeated interaction can change that logic,
• then test whether agents can discover that transition through learning.

Logical Path for This Section

1. Prisoner's Dilemma (one-shot): defection as baseline
2. Iterated Prisoner's Dilemma: when reciprocity can become rational
3. Bridge via MARL: solving the iterated game with independent PPO
4. General learned-cooperation theory in ecological systems

What This Gives You

By following this order, the reader sees:

• why cooperation is difficult,
• why repetition matters,
• how MARL can operationalize that theory,
• and where learned cooperation is stable vs fragile.

Go Further Toward Cooperation

After this section, there are three natural directions:

1. Toward broader social cooperation: Cooperation (Social Behavior)
2. Toward inherited cooperation (nature): Selected Cooperation Theory
3. Toward the bridge between both: Learning-Selection Interaction Theory