The Hunt for Intelligent Life
In fact, no-one really knows the probability of life starting from scratch full-stop. I can tell you though it's something extremely small since life is truly a miracle. But we're lucky it did happen. Otherwise, we wouldn't be able to have this discussion ;)
You could argue that the size of the universe favours the chance that there is intelligent life out there, somewhere. True. The univerise is, to put it very mildly, exceedingly large. So large in fact most people, like me, cannot comprehend how large it truly is. If there is an intelligent civilisation out there speaking or listening to us, it will be an incredibly long wait until we've heard from them (or they've heard from us) and we've decoded their messages (or they've decoded ours). We'll probably be space dust by the time one of us hits the reply button.
Hence, I think it's all bit of a lost cause. I'd be interested to see a counter argument though. I might be persuaded to join the other side. For now we're better off looking for intelligent life here on Earth.