Mutant strains should have been selected for by evolution and now be dominant.
I don't know what that is, but it looks like some weird combination of verbiage, jargon, and alien syntax.
What's it mean?
It's evolution 101. Self-destructive berserker strains would have self-destructed. Mutants with better survival traits wouldn't have.
That presumes the "self-destruction" event isn't flamboyant enough to take said "mutant strains" out as well.
But honestly, I just don't think broadcast communication is going to be used for a very long period of time by any civilization because of gross energy inefficiency, regardless of the specific wavelengths used, regardless of even the medium used (gravitic versus electromagnetic etc.). Tightbeam transmissions, or even better, lasers, give you better bang for your buck over large distances.
Consider the wireless networks we are currently using and continue to deploy. They are only broadcast (and even that with a highly directional emitter) over the "last mile." Everywhere else, the communication is either over hard-line or again, highly directed emissions to and from satellites. The "last mile" transmissions aren't going to be detectable over the background noise of space for very far at all (I don't have exact numbers, someone could prove me wrong here). The communications to and from satellites are so directional that even if their power was sufficient to be detectable over RF background noise at interstellar distances (which I very much doubt), you would have to have a receiver at just the right spot. And, since the Earth is rotating and the satellite is orbiting, the signal is going to be rotating in direction.
So, I don't think we can infer too much from the fact that we haven't heard anything yet.
