I should point out that it's not at all surprising that the "top 4" rats performed very well. If you got a couple of hundred people, animals, or random number g

I should point out that it's not at all surprising that the "top 4" rats performed very well. If you got a couple of hundred people, animals, or random number generators to trade using any set of rules you like, and then looked at the top 4, you would almost always find that they outperform, because that's what being in the top 4 means! The real question is whether the same four rats would be the outperformers if you ran the experiment again.