Of course not all life supporting planets will develop sentient tool using species. Unless there's something about sentience and tool use feedback loops that produce tachytelic development. That would boost the Drake estimate into the low thousands. We ought to be tripping over little green things.
But we don't. Of course if technological civilizations all self-destruct quickly this would all make sense.
- Refining the Drake equation: earth like planets more common? 10/2006
- Another stab at the Drake Equation – from the physics archives 10/2008
- SETI, the Fermi Paradox and The Singularity: Why our search for extraterrestial intelligence has failed 6/2000 originally
- Narrowing the Drake equation - if earth is common then ... 2/2009
- SETI: find one of nine galactic civilizations 11/2007
- How often will sentience evolve on earth? From anthropology to the Fermi Pardox - via the Drake Equation 2/2006