No planet is more earth-like than Earth itself, so if life really does pop up readily in earth-like conditions, then surely it should have arisen many times right here on our home planet? And how do we know it didn't? The truth is, nobody has looked.

The Eerie Silence: Renewing Our Search for Alien Intelligence (ed. Houghton Mifflin Harcourt, 2010) - ISBN: 9780547488493