It turns out rat society is much more complicated than I at least thought, and it definitely changes dramatically once it reaches a critical mass.
> Is this a totally reasonable thing to say, though, comparing us to rats in this situation?
I don't know. It depends on how generalizable social behavior is. I think it's very worrying with the problems we see with socialization in the world today and behaviors that, by analogy, resemble what's going on in Calhoun's experiments. We also have some anecdata from other social animals experiencing different types of collapse, where even though there is the physical capability of reproduction, the social collapse prevents it from occurring.
> Rats have no concept of extinction or death, humans do. To me, that means a lot.
What we abstractly know, for better or for worse, generally has little do with how we act. For example, human populations that experience severe trauma have problems even generations later, despite all their knowledge that their behavior is counterproductive.
I'm very curious how they found a control group for this. Generations, plural, encompasses, among other things, both world wars, and their aftermaths.
Not to mention, rat society doesn't change much whether it's ten rats or a hundred. Human culture becomes very different as people aggregate together, so whose to say that the very same social conditions triggered by increasing population will not themselves be changed by decreasing population?