[erikpukinskis]

I think the first time I heard about it might have been on this Planet Money episode: https://www.npr.org/templates/transcript/transcript.php?stor...

But I'm not really sure. This Google search links to a bunch of papers on the subject. It's a well explored area of research:

https://www.google.com/search?q=repeated+prisoner%27s+dilemm...