Comment: The Great Filter

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The Great Filter

With no evidence of intelligent life other than ourselves, it appears that the process of starting with a star and ending with "advanced explosive lasting life" must be unlikely. This implies that at least one step in this process must be improbable. Hanson's list, while incomplete, describes the following nine steps in an "evolutionary path" that results in the colonization of the observable universe:

1 The right star system (including organics and potentially habitable planets)
2 Reproductive molecules (e.g., RNA)
3 Simple (prokaryotic) single-cell life
4 Complex (archaeatic and eukaryotic) single-cell life
5 Sexual reproduction
6 Multi-cell life
7 Tool-using animals with big brains
8 Where we are now
9 Colonization explosion.

According to the Great Filter hypothesis at least one of these steps - if the list were complete - must be improbable. If it's not an early step (i.e. in our past), then the implication is that the improbable step lies in our future and our prospects of reaching step 9 (interstellar colonization) are still bleak. If the past steps are likely, then many civilizations would have developed to the current level of the human race. However, none appear to have made it to step 9, or the Milky Way would be full of colonies. So perhaps step 9 is the unlikely one, and the only thing that appears likely to keep us from step 9 is some sort of catastrophe ......

http://en.wikipedia.org/wiki/Great_Filter

Leges sine moribus vanae