An intriguing paper published on the ArXiv preprint server today discusses the length of time for which planets are habitable, and the implications for SETI experiments.

The paper, by Fergus Simpson of the University of Barcelona, discusses two scenarios for the development of intelligent life. The late appearance of humanity implies long development times, and thus the common conclusion is that intelligent life is rare. This paper provides an alternative explanation, which is that habitable conditions exist for only brief periods on many planets, but the development of intelligent life is almost inevitable.

The preprint is available here.