Consider that ideas (even facts!) might be like mind-viruses: you could imagine they propagate themselves in human minds, but are not actually produced by those minds. What if human minds are just the substrate?
Perhaps the earliest "ur ideas" were something like instinctive emotions. Even very simple creatures seek food and avoid noxious stimuli. Is hunger an idea? Maybe from hunger arose desire, and from desire arose searching, and from searching arose planning... Ad astra per fame.
The same way viruses change: usually recombination, but sometimes random mutation. Yes this happens in a human mind, just like viruses change within cells. The point is to focus on ideas as self-propagating and humans as merely vessels, rather than the other way around as people usually think about them.
interesting book on memes.