There are bigger problems with the evolutionary argument: AFAIK, catnip is first attested in Italy, and I have not seen anyone discuss finding a lot of catnip i

There are bigger problems with the evolutionary argument: AFAIK, catnip is first attested in Italy, and I have not seen anyone discuss finding a lot of catnip in the historical ranges of Felis lybica, that domestic cats come from; how can they have evolved to exploit the benefits of catnip if it's not there while they are evolving? Seems like you'd need a lot of wild catnip for such a selective behavior to evolve, but in the deserts where they live, there might be none. (Catnip isn't a particularly desert-tolerant plant.) Then you have the fact that something like a third of cats are immune to catnip & it's highly heritable, even though if it's a good insect repellent (that's quite fitness-relevant), there's really no reason for it to not have reached fixation quickly and become a 100% frequent trait. Further, catnip response across all of the Felidae species is super-inconsistent, with very far flung species showing some catnip response but also closely-related species showing very different responses; if it's under selection, they ought to be similar, and anyway, there may or may not be catnip where Felis lybica grew up, but then what about South American felines half a world away...? Finally, if you feel that you need an evolutionary explanation, then what is your explanation for all of the other cat psychoactives like valerian, Tartarian honeysuckle, silvervine, the Indian one, and so on? If you don't think there is one, and that, like most human psychoactives, it's just because biochemistry is really complex and stuff happens, then surely that shows catnip didn't need one either.