This, surely, was a matter of chance. Which figure you choose depends on your optimism. It is always difficult to extrapolate from a single instance. This figure, however, is of some importance when you are dealing with the limited number of planets that can be reached by any of the SETI projects. Physicists, on the whole, will give a different answer to this question than biologists.
Physicists still tend to think more deterministically than biologists.
They tend to say, if life has originated somewhere, it will also develop intelligence in due time. The biologist, on the other hand, is impressed by the improbability of such a development. Life originated on Earth about 3.8 billion years ago, but high intelligence did not develop until about half a million years ago. If Earth had been temporarily cooled down or heated up too much during these 3.8 billion years, intelligence would have never originated. Evolutionary pathways are highly complex and resemble more a tree with all of its branches and twigs.