There may be a lot of life in the universe. Part 3
So how can we judge whether intelligence is a likely evolutionary development or not? We do the obvious, and look for hints in Earths history. Earth is, after all, the only example we have. Since high IQ critters appeared here, theres a tendency to assume that our planet is just another typical, run-of-the-mill rocky world, and what happened on our planet might happen on their planet, too. Sooner or later, intelligence will arise.
But there are flies in this ointment. Sixty-five million years ago, a rock the size of Brooklyn slammed into the Earth, wiping out three-fourths of all species, including the dinosaurs. If this hadnt happened, the rat-like mammals that eventually evolved into Homo sapiens wouldnt have inherited the world. And 245 million years ago, another catastrophe (known in polite society as the Permian extinction) wrote finis to an even larger percentage of species. These cosmic accidents were all forks in the long road that eventually led to us. Maybe on other worlds, the road never gets that far.