Logically,
we are not.
Before the last century ends, it's been confirmed by NASA through its Hubble Telescope that there are other Solar Systems beside our own. Some are older than ours, while others are still "babies". This is a confirmation of the theory that Copernicus, Heraclitus and later, Father Giordano Bruno were postulating centuries ago.
My own view is this: If our own sun is just a star when viewed from far-off distance, then it's easy to conclude that those stars we see at night are also suns of their own Solar Systems, right? If so, then, we could also be right if we conclude that in one of those Solar Systems, one planet maybe populated by Intelligent Beings just like us. They could, of course, have their own physical attributes, and unique way of life.
What if there are other Universes other than where we are? That surely would compound to the veracity of our postulation - that indeed there are other civilizations out there, much or less advanced than we are.
So, with simple application of logic alone, we can say that it is foolishly "selfish" for us to claim that we are the only Intelligent Beings in this whole wide world, aren't we?
Empirically,
we are not.
Evidence no. 1

Since we have not yet set foot on it, this image taken by Malin Space Science Systems on Mars is open to all our speculations. Bear in mind, the tube-like structures are of enormous size considering the distance the image was taken from.
Nevertheless, the first logical question would be, "Are these tube-like structures natural or not?" If it is natural, then how it arrived to such a "complicated" form?
If it is not natural, who created it, what is its purpose? Are the inhabitants of this planet are, for some reasons,now living underground? What do they look like?
What if those inhabitants have abandoned such planet in favor of what is to be called as Earth? If so, in chasing the future are we now in fact tracing our past?
Evidence no. 2 Among the anomalies observed in the above video are:
- shooting stars that changed direction
- objects swarming towards man-made structures
- objects flying in formation above the horizon
- unedited conversations of NASA astronauts regarding observed UFOs flying by