I would assume they came at the same time seeing as time doesn't really matter or exist or umm whatever you call it and all thoughts have been thought by somebody, somewhere, here there and everywhere you have not been, because if you had been there and known it, you would not ask questions like this. They may be getting thought right now just because. If you were willing to, you may just feel the need to think it too, but really is it worth it, no no... rather, what is it worth? I would think it is only worth the brain that thought it and ours barely works so stfu and squeeze your wimsum into some cowpung.. oh and ride ya bike there and back.
I've had my own ideas before I even heard of existentialism. I didn't know what it was until someone explained it to me. It kinda freaked me out as first how well it just clicked.
benign strangeness is something i've been discouvering all my life. as for existential, that's just something some people have occasionally called me, for reasons of agendas i've yet to entirely comprehend.