Is intelligent extraterrestrial life common in our galaxy?

No alien civilizations have substantially colonized our solar system or systems nearby. Thus among the billion trillion stars in our past universe, none has reached the level of technology and growth that we may soon reach. This one data point implies that a Great Filter stands between ordinary dead matter and advanced exploding lasting life. And the big question is: How far along this filter are we?

In my view, life in the form of microbes or their equivalents is very common in the universe, perhaps more common than even Drake and Sagan envisioned. However, complex life -- animals and higher plants -- is likely to be far more rare than commonly assumed. Life on Earth evolved from single celled organisms to multi-cellular creatures with tissues and organs, climaxing in animals and higher plants.

...if advanced civilizations have evolved in many of [the countless other solar systems, many of which are billions of years older than ours] then some have a vast head start on us — so where are they? I don't buy the explanation that they're all choosing to keep a low profile: natural selection operates on all scales, and as soon as one life form adopts expansionism (sending off rogue self-replicating interstellar nanoprobes, say), others can't afford to ignore it.