The Great Filter is a proposed reframing of the Fermi Paradox, introduced by Robin Hanson in his 1998 essay The Great Filter - Are We Almost Past It?.

The development of space-framing intelligent life requires many steps to occur in sequence, such as the emergence of single-celled life and the transition from unicellular to multicellular life forms. Since we have not observed intelligent life beyond our planet, Hanson argues that there seems to be a developmental step that is so difficult and unlikely that it "filters out" nearly all civilizations before they can reach a space-faring stage — a "great filter".

From Hanson's essay:...

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