I don't remember where I saw this information but some astrophysicist was describing the astronomical (couldn't think of a better word, sorry) size of the known universe and how given that size, unless other alien species are unimaginably more advanced that what we can even conceive of, that encountering other intelligent life is exceptionally small. I hope that if it does happen that other species have a very different demeanor than humanity does though, because we would just destroy the other population.