I doubt any have intelligent life though... http://richardkulisz.blogspot.com/2007/04/aliens-dont-exist.... Apologies for Richard Kulisz's more asinine qualities, but I've never seen a convincing refutation of the argument he presents there.
He claims to start with one assumption, but actually starts with many. For instance he implies "any species which could colonize the galaxy, will". I don't accept that all possible intelligence would try to take over the galaxy. He also says that it's not in an alien's interest to leave one planet (Earth) just in case we develop - but he doesn't consider that they might have colonized the galaxy but left Earth precis…
He completely ignores that humans actually took many tens of millions of years to evolve from scratch not from existing life forms.
Kulisz responded:
The point is that it didn't have to. Nothing in the universe prevented a technological civilization from arising 8 billion years ago. And certainly not 65 million years ago back when the dinosaurs ruled.