“Must Early Life Be Easy? The Rhythm of Major Evolutionary Transitions”, 1998-09-23 (; backlinks; similar):
If we are not to conclude that most planets like Earth have evolved life as intelligent as we are, we must presume Earth is not random.
This selection effect, however, also implies that the origin of life need not be as easy as the early appearance of life on Earth suggests. If a series of major evolutionary transitions were required to produce intelligent life, selection implies that a subset of these were “critical steps”, with durations that are similarly distributed. The time remaining from now until simple life is no longer possible on Earth must also be similarly distributed.
I show how these results provide timing tests to constrain models of critical evolutionary transitions.