[xrp]

Not to mention that, assuming what we regard as a path of evolution, intelligent species at some point use radio waves to communicate with each other, if any other intelligent species developed in the last 80,000 years in the Milky Way (since no point in the Milky Way is more than 80,000 light years from Earth), we would have detected them because of their radio waves.

So, from an arrogant, Earth/human-centric point of view of the Milky Way Galaxy, there has been no other development of intelligence in the Milky Way Galaxy at least as of 80,000 years ago.

[RightWhale]

The other point is that galactic civilizations may arise, but they may also burn out. There may have been dozens of civilizations pass through the Solar System in the past millions of years, but none are here now. It is possible we are the remnant of one of the latest ones to pass through.

[Steve Eisenberg]

Not to mention that, assuming what we regard as a path of evolution, intelligent species at some point use radio waves to communicate with each other, if any other intelligent species developed in the last 80,000 years in the Milky Way (since no point in the Milky Way is more than 80,000 light years from Earth), we would have detected them because of their radio waves.

No. By the time we built radio receivers with sufficient sensitivity, the airwaves had too much interference from earthboard broadcasts. Plus there is the interference from weather, lightning, etc. We need to put a radio probe on the far side of the moon to get over this.