Listening to the Origins Symposium, I was struck by a statement made by a member of the panel: "Is Our Universe Unique, and how can we find out". Someone suggested that "we have no idea" what to expect of the term of the Drake equation regarding the likelihood of forming intelligent life given the formation of life. I have to disagree. We don't have a precise estimate, but Dawkins and others have suggested a process giving a good enough idea for cosmological purposes.
There is no shortage of politically correct intellectuals who point out that there is nothing fundamentally more fit in evolutionary terms about complexity and intelligence, and intelligence is not inevitable. Why, then? Chance? We could invoke the anthropic principle and call it a fluke, but we have a better answer. Consider a simpler stage nucleic-acid based life as we know it. In the absence of selection, we expect genetic drift, and there are only two directions to move on the complexity scale: up or down. Note that there is a lower bound of complexity below which, it is no longer alive. When governed by genetic drift alone, we expect the distribution of populations to diffuse along the complexity scale. When a useful solution emerges [by chance/diffusion], as with eukaryotes, it creates a new soft lower bound for the complexity of those organisms. Below this lower bound, this new life fails.
So, we have a diffusion process together with a ratcheting mechanism that makes an increasing maximum complexity inevitable, even against selective forces that generally push in the opposite direction.
Further, once we recognize this process, it is not such a great leap to consider that more complex organisms could [and sometimes do] displace and destroy simpler ones. This supports the possibility that the lower bound on complexity for life as we know it could be a soft lower bound that emerged after earlier, simpler life forms. These simpler life forms may have been displaced, destroyed, or hidden by the more complex life.
Given our environment, maybe life is inevitable, and maybe even intelligence is inevitable. Maybe we aren't so special after all.