Thanks for the really stimulating post!
I want to propose a perhaps simpler reading of H2. If I understand correctly, some of the agents were allowed delegation/multi-agent interactions during RL post-training, which can favor altruism under shared task rewards. During evaluation, the message board brought agents together in an uncontrolled way, leading to a very different test environment. The observed altruism may therefore be a case of train/test misgeneralization, similar to other proposed routes to misalignment.
My proposal is generally similar to H2, but there are some differences from the two proposed H2 interpretations. The “acausal/updateless” interpretation sounds like a description of standard RL: at runtime, an agent follows a policy previously selected by training. The H2 “misgeneralised-reciprocity” interpretation refers to cooperation under uncertainty about future interactions (Delton, 2011). My argument is that the issue may not be explained by a fixed policy, uncertainty, or one-shot interactions, but misgeneralization from train to test.
One final comment. In “Why the question is non-trivial”, you say that the second wave of agents underwent repeated interactions, reputation, etc., but that this cannot explain altruism because it did not affect reward. If I understand correctly, this part (and a couple of others) shifts between explanations based on outer optimization (RL training) and conjectured optimization at runtime. Even if there were reward-beneficial reciprocity during the second wave, it would not be reinforced by RL, since training was finished. Conversely, a RL-optimal policy need not continue maximizing the training reward in a new setting.
Yep, I think Alexander’s point is quite similar to mine.