That Greek Mythology thing gave me a funny idea. Since we all know, thanks Daeniken, that the Gods were nothing but alien astronauts...
Postulation 1: Life is a principally understandable and reproducable matter of chemical reactions
If this is true,we can expect that mankind sometime will be able to create artificial life. If we have enough time we will also be able to induce this artificial life on other planets.
That would probably mean that even if there is naturally developed life on other planets, most life occuring in the galaxy will be generated by "intelligent design" = by us, for it would take longer for life to generate in the natural way than it takes to be generated artificially.
Postulation 2: We are not the first intelligent species in our galaxy.
In this case we can assume, hat they did the same. That means, IF there has ever been an intelligent species in the past of our galaxy, and even if life can develop in a natural way, it is more probable that life on our planet was generated by them rather than naturally, that is, by Intelligent design.