Since nobody pointed that out yet: rat utopia results are questioned now, based not only on a fact that the enclosed space where rats resided were sitting in direct spotlight, but also on a replicability issue. An experiment with results that couldn't be replicated should be dismissed.

It's entirely possible that the mice in this experiment were overheated, and dominant males didn't fight to "stay in solitude" but rather to be out of direct sunlight.

That's to say, if the cause for such mouseslaughter really was in the temperature, climate change could make original experiment relevant again.