When you really think about it, you'd be crazy to think otherwise. Quoting Carl Sagan, "There are more stars in our universe than there are grains of sands on all the beaches in the world", And on most of them stars, planets orbit them. Actually, recently the NASA's Kepler Telescope found 'earth-like' planets orbiting the star Gliese 667, the planets are in the habitable zone, so the chance that they harvest life is a possibility.
The vastness of our cosmos is absolutely mind boggling and no one can truly begin to comprehend it.
Astronomers find new planets that lie within the habitable zones of various stars every year. And they have only looked at the tiniest fraction of the universe. Even if a planet like Earth only has a 1 in a billion chance of developing life at all, and then only another 1 in a billion chance of advanced life like humanity evolving, there are still countless worlds that likely harbor intelligent life.
Assuming that 'others' refers to sentient life and not humanity. I am absolutely positive that somewhere out there, in the vast potential of life and space, there IS some other lifeform. I just hope they aren't anything like us. Humanity by and large is a disease upon the planet. It shares all the same qualities and markers of a virus. While we certainly have the potential to be more, we aren't quite there yet. Here's hoping that the planet can survive our adolescence because I'm fairly sure we wouldn't be too well received elsewhere.
I betcha anything. There is likely more life forms like us and maybe dinosaurs, possibly there have been other civilizations like ours today that have existed billions of years ago out there. Watching tv, going to work, getting married having kids and had an astroid wipe them completely out millions of years ago. I would bet there is billions of other planets out there now, and in the past with some similar and other mind boggling types of life.