Bryce, the only hard, absolute and irrefutable evidence we have to date of intelligent life existing elsewhere in our Universe is the fact that thus far they have NOT contacted Earth.

All humor aside, to quote Arthur C. Clark's 'Third Law', "Any sufficiently advanced technology is indistinguishable from magic." Thus, we may well lack even the most basic means of recognising and identifying alien life forms we encounter, even if they do exist.

My personal take on 'intelligent life' is that we humming beans have a vastly overstated and overestimated opinion of ourselves, as regards 'intelligence'. I feel that on any possible comparable cosmic scale, we are likely so primitively developed that we would be considered mere protoplasmic 'pond scum' by any truly advanced civilisation.

If any evidence of that is needed, all one needs to do is look around at how we 'highest evolved sentient life forms' interact with and treat each other. The evidence here speaks for itself, QED.