What is significant is not merely that some aliens don’t engage in large-scale stellar engineering, but that all aliens don’t engage in large-scale stellar engineering, to the extent that we can say that large-scale stellar engineering doesn’t please Gnon. We can even say that spreading life throughout the galaxy (if we had to will to do this it’s something we could be doing, and in such a way as to create a snowball effect where once started there would be no stopping it until the galaxy was saturated with life, which is why there is a sense of imminent impact) and conserving energy within the galaxy also doesn’t please Gnon. This is startling and significant because it also contradicts our priors meaning we have to adjust our priors. This is why theories like being in a simulation are taken seriously. This is why the technological singularity is taken seriously.

And no, junk DNA is probably mostly junk DNA. (1) We have over a century of systematic work looking hard for the behavior of inherited characteristics for various reasons, including pragmatic plant and animal breeders, curious scientists fiddling with variant neurospora and drosophila and mice, and physicians trying to understand heritable human conditions. Over and over again when we figure out how some malfunction or adaptation works, it turns out to fit the ordinary Darwin/Mendel/DNA/centraldogma story that says the non-junk DNA is where the action is, and the exceptions that test the rule (like jumping genes, trisomy 21, or adaptive genes spread between organisms by non-Mendel mechanisms like viruses) can be strange but still generally don’t mean that any large proportion of junk DNA matters. (2) We have accumulated enough DNA sequence data that we know a lot about the statistics of evolution of DNA patterns over time, and the patterns of change in most junk DNA look enough like unconstrained random accumulation of mistakes — very different from the evolutionarily constrained changes in the bits of DNA that code for functional things like proteins — to give a *lot* of evidence that the junk DNA doesn’t affect reproductive fitness in any sharp way. (You may ask: what would be a not-sharp way? E.g., a constraint that two genes not be too close to each other on the same chromosome.) We also know enough about the math (of information theory, genetic algorithms, and the like) to expect junk DNA as a consequence of plausible estimates of the fitness constraints on evolving organisms. Neither (1) and (2) are evidence the recent results on heritable Lamarck-style adaptation are necessarily bogus, but they are strong evidence that such a phenomenon would be a rare anomaly.

What if the activities of really advanced civilizations are indistinguishable from natural phenomena to us? How do we know for sure that the universe we observe is entirely uninfluenced by intelligence? Our relatively primitive ideas of what intelligent activity looks like may be wrong.

I have a blog series that touches on this, http://raymundeich.com/tag/fermi-paradox/

Carl Sagan wanted to reduce the US nuclear arsenal.
Carl Sagan played up the effects of nuclear war as ‘nuclear winter’ as a means to that end.
Carl Sagan played up the effects of ‘nuclear winter’ by arguing high-tech civilizations arise easily, but each such civilization inevitably destroys its home planet in a nuclear war before it can spread outside its home stellar system.
(You may have noticed he elided how his desired US policy outcome would cause humankind to escape this “inevitable” fate).