[jennyp]

I'm still thinking in Rare Earth mode. Until we have some baseline examples of extraterrestrial life, I'm of the opinion that the accidents that led to intelligent apes are rather uncommon.

I've changed my thinking about this lately. I think intelligence of our level may be rare, but complex multicellular life will be common. I say this because the Earth itself has contained a staggering number of different local environments over its lifetime, so I think we already have a good statistical sampling of the possible types of organism. (At least what we should find on an "earth-like" planet.)

Bacteria form the majority of the biota on Earth, and yet there are millions of species of multicellular life as well.

[js1138]

I have no problem believing that complex life is common, but the existence of big-brained animals without language leads me to believe we are rare, perhaps as much a product of geology and catastrophe as biology.

[PatrickHenry]

I think intelligence of our level may be rare, but complex multicellular life will be common.

Then we'll be rulers of a galaxy populated by nothing more advanced than clams and slugs. Not very stimulating company, but at least they might taste good.

[Virginia-American]

Bacteria form the majority of the biota on Earth,

and for half of the history of life, they were the only life on Earth.