I find it hard to believe that it only takes 20 specific conditions to create intelligent life. I think it is far more complex than that but take for instance the dinosaurs. These creatures were able to exist on the earth when it was far less habitable. Supposedly the earth was covered by volcanoes and was probably a lot hotter than it is these days. I think it is very plausible that there are other planets covered by desserts or volcanoes and are still able to maintain some reptilian lifeforms. According to some of the books that I've read a planet only needs to be able to sustain algea to eventually produce intelligent life and algea can sprout up almost anywhere when certain conditions are met - I am guessing this is the 20 conditions that are required for life on earth as well.