Wow, so that’s it. All this time I have been wondering. Still I am a little skeptical of this, but I would not be surprised if there were something to it. (my cats go outside a vast majority of time anyway so the benefit for me may be minimal…) I saw this thing about intelligence, test scores, linked to DNA. I think there is evidence that a wide variety of unknowns, bacteria, viruses, DNA, etc., affect many factors in human behavior, good and bad - that is the weird part, the good I mean, we expect the bad. I remember watching this documentary about how chimpanzees used some tree, its leaves on wounds, etc. Turns out people use it and it appears to even have properties that may offset cancer. The world is a complex place; there are probably a lot of interactions going on like this.