Nuke, that is exactly[/] possibility 1, that we are the First intelligent life that the Universe has spawned, even now there may be others on a slower path perhaps only having entered the Stone Age or perhaps their development was halted during their "Greek" Era somehow.
In order for us to be able to detect them they would need to have been at the same level as us and proceed at a similar or slower rate. That means that none of the stars within ~14 parsecs(60 lightyear) have advanced life around them or one(or more) of them have life that is more advanced than us, perhaps radiacally so.
There are some few who believe that we were put here by another race in order to develop socially into beings who, while perhaps not craving it like Klingons, are very good at battle and that one day they will return and claim us for use as shock troops in interstellar warfare.
Others believe that the myth of Atlantis was actually a group of expatriates from somewhere else that came to this world to seek a hiding place and that they commited the a cardinal sin by engineering us and cross-breeding(the Nehpilim).
There's no end to the wild theory's, but the realities, once contemplated seem to put the kibosh on that kind of fanciful thinking. Even for a nutjob like me.
If you're wondering what brought this on, go read Ring by Steven Baxter, which basically details the death of the universe and the survival of the human race(all 2000+ of us, half of whom are over 500 years old and one is over 1000). It is really kind of depressing.
