How common is life in the universe?

The question is basically unanswerable. The well-known Drake equation feigns a certain degree of precision but suffers from the fact that it is nearly impossible to reach agreement on values for any of its seven factors. Right now, we have only one example for intelligent life, and for us to draw conclusions for the entire universe from just our own existence would, indeed, be very human, but would be scientifically problematic.

There is, however, an alternative. We could ask what the likelihood...