What I mean is, in the HP-verse, were the pets always sapient, bipedal, and as long-lived as they were, or were they made to be that way somehow? Could it have been a science experiment gone awry, a bad round of cosmic D&D, or just always that way?

Rick once wrote a short novel titled An Infinitesimally Short History of something or other that explains a lot. I have not found it to read it, but it should help you out.

I don't think he ever made public any of it other than what he posted on Housepets!
only his beta readers have seen anything else

Yea, as far as my Google-fu can tell it never saw the light of day. At least not that I've been able to find.

I believe he is still editing it but working slowly on it because he has a bunch of other things to do and doesn't consider it important. While it would be canon to the comic; IIRC nothing in the novel is going to affect the Comic in anyway so people will not have to actually read it to get what is going on in the comic. Its just supplemental material really.

Yes, but it does explain the origin of species in the HP! world, I would assume.

Huh, I always assumed it was always like that. Grape did mention a wolf actor from the 30's during the "Hope of the Pridelands" arc, although and eighty year span really isn't that long in the big picture. It's something that no one ever found strange, and even the feral animals seem just as intelligent as the pets, regardless of species.

When it comes to a work of fiction, it could be a case of "always been like that", but I'm not sure now that you've brought that up.

In this text: http://www.housepetscomic.com/2010/11/0 ... s-7500-bc/ it's said that talking cats existed for millennia before the start of the webcomic. So yeah, I assume that this just a version of Earth were animals talk.