Yes, there are. How do I know? Because it's rather ridiculous to think that out of all of the planets and galaxies is this vast and mostly uncharted universe, that no other intelligent life exists.
It has to!
Doesn't mean I don't believe in God.
From a biblical perspective, that is a weak argument. We're applying a human perspective on time and space, and assuming, if you think about it, God Himself has this same view of the vastness of His creation. But the size of the universe is nothing to God. So i can easily see humanity being the unique creation in the known sphere of existence of humanity. God granted us this universe as His gift to us, just because it's vast, doesn't mean it's populated. This may be unique for us and us alone, as an expression of Gods love and affection for us.
Now that's to say that i'm claiming that it's impossible. God is big enough that he may have 1000s of other living creations out there we don't know about. But to automatically assume the speck of our existence is anything to God that he would feel a need to fill it up with other species, that it 'must' be true is not logical. Only possible.
Personally, i'm more inclined to believe there would be other creations outside our realm of existence and awareness. God exists outside of us, our universe, maybe there is another universe, another existence, outside of us that He has created as well.
But even scientifically speaking, leaving God out, the pure chance of human existence is so unlikely it's nearly impossible. To assume a near possibility has occurred more than once, to that degree, as something that 'must' have happened, just doesn't jive.