Simple life is probably wide spread throughout the Universe. But I'm talking about Bacteria or single cell organisms. Animal life or Complex life on that level is probably extremely rare if it exist at all else where. Of course, given the massive size of the Universe, I would say animal life does exist somewhere else besides Earth. But then the next question is how often does complex or animal life develop into intelligent life? I would say the ratio is probably the same as Complex life is to simple life. Very very rare.
If your really interested in this subject from a scientific and objective stand point, I suggest you get the book "Rare Earth". Its an investigative book on the subject of how common complex life is beyond Earth. Its written by an Astronomer and a Geologist and in general reflects most scientist thinking on this subject matter. There is even a hypothetical math formula in the book to help determine an estimate for the possible number of planets that might have complex animal life. Trust me these guys have done their research and it is all scientifically based and explained. While they do not reach a conclusion that complex life does not exist elsewhere, they do provide evidence that clearly shows that complex life far more rare than most people including some other scientist had thought. After reading this book, its amazing that were actually here, and you'll begin to understand why complex life is probably so very rare if it exist at all outside of Earth.
I think that probably only 10 star systems out of over 300 Billion just in our Galaxy have or have ever had complex life on one of its planets. I don't think any of them ever developed into intelligent life. As for Intelligent life, I'd say that is so rare that only about 1 in 1,000,000 galaxy's actually have an intelligent form of life. By intelligent of course I mean on the level of man or higher. This means that the nearest intelligent species is probably in a Galaxy at least 50 million light years away! In general, intelligent life is so rare and so spread out that I doubt that any intelligent species will ever contact each other given the unbelievable distances. Its like trying to find a single special marked needle in area the size of the USA or greater.
Aliens probably exist, but will probably never find them nor they find us or anyone else do to the vastness of space and the rarity of intelligent life.