(Sorry, I've exhausted my ideas on alien life!
) No, but surely you can't be saying that a significant number of intelligent advanced civilisations will exist in the region of 5 to 50 million years - each civilisation is of course starting from scratch - I can't even imagine a civilisation last 1 million years, not even much more than say 10000 yrs given we're in year 2000 (albeit we have BC knowledge), but I can't imagine 1,000,0000 or even 5,000,0000 or even 50,000,0000 that you mention. Too much can go wrong.