In order for institutions to spread, it needs to overtake a set number of institution spread, which increase every institutions in the game, kind of like cultural dominance over a territory already in the game. Every turn a civilization doesn't adopt an institution, it takes an about 5 percent decrease in its science generation and maybe -5 stability in all cities. (I haven't really thought the numbers out well), and around 12 institutions per game.

So an institution spawns in the most populous city after a set number of cities founded, maybe something 6, 8, 10, 12 cities, etc. I feel like a similar form for institutions could be applied to humankind, (but not outright the same as that's bad). So EU4 has something called institutions, in which it limits the tech generation of countries that haven't adopted this institution.