And 'evolutionary adaptation' is irrelevant. We can change ourselves (are changing ourselves) genetically already. That will only increase. The result will be a species more adaptable than any in a billion years. If it has the will to colonize other planets, it certainly can.
'A shred of evidence' is really not hard to find, if we aren't needlessly negative and contrary.
20 years ago, before we had direct evidence of exoplanets, we had evidence from the spectrum of stars that about 80% of the ones which had grown large enough to swallow any of their planets had previously had gas giants.
All of the resiliency that you've seen in life is due to the fact that the environments to which we're adapted are uniform. Oceans everywhere are nontoxic and water. Air everywhere is mostly clean and breathable. There is no example of life being resilient under conditions as varied as other planets. We are only able to adapt within the confines of our clean-room Earth. We can't even adapt to the bottom of the ocean or Antarctica.
Optimism isn't going to overcome 6 orders of magnitude of error.
To get people to tolerate more salt, we'd have to have a fish's ability to regulate it. Ok, genes for that. Air issues? Filters, microstructures to migrate particulates out, baffles (like many creates already have). Deep-ocean pressure? Only a couple of issues there, and certainly life thrives at the bottom of the ocean.
It's not optimism; its simple observation of what we have already on Earth in existing life forms.
And 30,000 years changes not a thing. The log of 1 Trillion base 2 is 39. In 40 generations of space colonization, that's 40 times 30,000 times however long it takes to rebuild the capability on each colony. In a dozen million years the galaxy would be covered. Its 20B years old. So, nobody's tried it yet.
Assuming each generation survives. Stop making that assumption, and see how many ways there are for you to reach a similarly empty universe.
>It's not optimism; its simple observation of what we have already on Earth in existing life forms.
I wish you'd observe that none of Earth's lifeforms have colonies on other planets. Goldfish didn't colonize other worlds, is that then a strong argument that Goldfish don't exist?
What you're saying makes no sense: just because animals can colonize a single planet over many generations does not mean they will be able to colonize an entire galaxy in even less time.
I would not be so sure about dolphins. ;-)
Or, to bring a concrete element to the question: all known rocket fuels require some nonrenewable Earth resource. How much fuel does it take to launch a vessel built with currently-known technology that would be capable of landing a living human being on a hypothetical planet around Alpha Centauri? And what does that fuel number look like, when expressed in terms of "years of current resource extraction" (or, somewhat more audaciously, percentage of known proven reserves)?
To my knowledge, interstellar colonization is flat-out impossible with current technology. (I'd argue that even intrastellar colonization is impossible, rather than impractical). Arguing that we should discount this non-knowledge of how to do it when explaining why it hasn't happened to our observation is irresponsible to me.
Methane + oxygen popular in the new generation of rockets is not much different, you basically add some carbon to the process & Methane can be made on Mars from local resources.
Best fuel for nuclear thermal rockets is again hydrogen, abundant everywhere.
Current Ion Engines run on noble gases, but supply does not seem to be a problem so far.
Sure, the uranium needed for Orion and Nuclear Salt Water rocket indeed is not really renewable but given the performance &opening the way to grab more of it from space make it a non-issue as well.