The fact that relatively high intelligence has arisen from many architectures multiple times on this planet bodes well for the frequency of intelligent life on exoplanets.
As I remember from the book "Power, Sex, Suicide: Mitochondria and the Meaning of Life" [1], the bottleneck may be not the evolution of the intelligence, and not even of life itself, but specifically multicellular life. There are reasons to believe it only happened once, and for about 1bn years before that life already existed in single-cellular form, which gives an idea on how improbable the step from single to multiple cell organisms is. I am vague on specifics though, but can wholeheartedly recommend a book to anyone interested in evolution and origins of life.
According to an interesting book of a Russian paleontologist Kirill Eskov [1] there were a lot of "evolutionary tries" to create a multicellular life. And as soon as it became "profitable" the regular try conquered the world.
IIRC it was related to increased oxygen level.
[1] "История Земли и жизни на ней" ("History of the Earth and its lifeforms")
Actually, I stand corrected - not the multicellular life evolved once, but the eucaryotic cell. According to the book, eucaryotic cell evolved by acquisition of mitochondria. Energy generated by mitochondria allowed the eucaryotic cells to be much bigger than procaryotic ones, and to support multiple different organelles.
Yup! The formation of the first Eukaryotic cell is a mystery. Eukaryotes have features of both bacteria and archea, yet doesn't have a clear origin in either of them. Here's a book that goes into more depth on the important stages of evolution: http://www.amazon.com/Major-Transitions-Evolution-Maynard-Sm...
On a tangent, my dismissiveness of creationists has only increased since reading The Major Transitions in Evolution. There are some really perplexing things in early evolution that we don't understand at all. And yet creationists like to talk about chimps and rocks.
As I remember from the book "Power, Sex, Suicide: Mitochondria and the Meaning of Life" [1], the bottleneck may be not the evolution of the intelligence, and not even of life itself, but specifically multicellular life. There are reasons to believe it only happened once, and for about 1bn years before that life already existed in single-cellular form, which gives an idea on how improbable the step from single to multiple cell organisms is. I am vague on specifics though, but can wholeheartedly recommend a book to anyone interested in evolution and origins of life.
[1] http://www.amazon.com/Power-Sex-Suicide-Mitochondria-Meaning...