Let’s do a little extrapolating from the present to the next few hundred years based on developments over the last few years.
We are sending automatic unmanned probes into space.
Artificial intelligence is now advanced and its development is accelerating
We are unlikely to send many human beings on long open ended trips with no return.
Combine these together and it becomes very probable that we will send highly intelligent machines into space to collect data and send it back to earth.
These machines will be capable of making decisions based on the circumstances they are in. Some will leave the solar system and head off into deep space for journeys that may take tens of thousand of years.
Humans, and probably any naturally occurring and evolving organisms, are simply not suited for this type of travel. Computers are eminently suitable. Needing only electrical power they could be run from a small nuclear source and can switch to a low power mode. Even a “thinking” being could survive the loneliness and the isolation if they could “compress time” by reducing their internal clock. A ten thousand year journey could appear as a day or two!
During this time it is quite possible that humanity may cease to exist – this could be due to a natural disaster or disasters such as comets, asteroids, super volcanoes, plagues, wars, severe climate change etc etc. In that case the only residue of our civilization would be the spacecraft we had sent.
Now, how many times has this happened in the past in the galaxy? How many artificial life sources are roaming the universe?
Well I don’t know the answer either, but I do know in an almost infinite universe the answer is certainly NOT zero. If we ever make contact with other intelligences, it is much more likely that the intelligence will reside as programs in alien machines, and not as little green men.
It may well be that it is peak of humanity’s destiny to join them. Their organic ancestors will be as remote to them as our amphibian ancestors are to us.
Now extend the extrapolation far into the future. More and more organic based civilizations will develop, produce AI type of descendants then die off. It is the destiny of the universe to be populated by AI.
I followed up this theory with a little story