In a book reviewed here by New Scientist the author argues that our circumstances and history on planet Earth makes it very likely that it is unique in harbouring life. I don't know about that. The universe is a big big place with, very likely, many trillions of planets like this one, some of which may have had a history that leads to the development of life, even intelligent life. But, on the other hand, does it make a difference? It is quite unlikely that we would be able to detect intelligent life in a distant system. If we did, it would be probably long dead. In any case, unless Einstein and all the main physicists of the 20th C. are wrong and the light speed limit can be got around, there is no way to have a two-way communication with a civilisation even a few light years away. So, in practical terms we are alone, unlikely as it may be that we are the only intelligent beings in the observable universe.