We have to be careful when looking at our history and assuming that this is the only way life can form and under our circumstances. Given how ignorant we are on the subject it's folly to try to estimate probabilities or to say that things can't happen any other way. Personally I think the universe is infinite and what we think of as the big bang is just some local perturbation in space-time. In an infinite universe other intelligent life forms exist, though they can be out of our reach.