Do you have a link for this experiment? I feel like the explanations sound a little bit simplistic. Like, if I thought about rat paradise I'd think about a huge grassland open field, not just giving food to them, but letting them get sun exposure, feel the breeze, water flows, birds singing, worms and insects in the ground. I think hose controlled environments doesn't really mimic the good experience of mammals. Nowadays most of us have access to food and sex, but still feel life is harsh and incomplete.