[denton-scratch]

> very long lived extraterrestrial civilizations

We're talking about stellar visitors that arrive every 20 million years or so. We have no evidence of any civilization that lasted much more than 1,000 years.

So you're going to hitch a ride with a stellar visitor, with a view to colonizing the galaxy? Suppose the visitor comes as close as a few thousand AU, and the colonist ship can reach it in a hundred years or so; cool. But how long before the visitor reaches the next star on its tour? That's going to be millions of years.

So the colonists set up camp on a planet orbiting the visitor; the hypothesis is "a very long-lived" civilization, so we assume they have brought their knowledge with them to this camp, from the home planet, and are able to conserve it (strong assumption). But for tens of millions of years?

Civilizations evolve much more quickly than organisms, if Earth history is anything to go by. It seems far-fetched that a civilization might survive the evolution of the underlying organism; there's something Canute-like about trying to preserve a civilization in the teeth of genetic evolution. Evolution is going to happen, even during the initial journey to the visitor.

I'm very sceptical about this notion of "very long lived extraterrestrial civilizations".

[pfdietz]

The civilizations themselves don't have to be long lived, but once a star system is colonized it has to stay inhabited long enough. Civilizations could come and go, but not completely die out too quickly. As long as each colonized star system produces enough child colonies before it dies out the exponential growth will continue, with colonies eventually being reestablished at systems where former colonies may have expired.

Eventually there would be selection for colonies that can produce faster and/or longer lived colony ships, so they can plant new colonies faster. This will eventually shade over into the more conventional galactic colonization scenarios where stars can be treated as near stationary.

[Vecr]

Technically, you can stop evolution from happening. Cloning is annoying, but if you had enough compute and algorithms you should be able to make in-place edits to stop drift. By "in-place" I mean even optimistically just a bit after the blastocyst phase, editing humans that are even slightly grown to that level is just not going to be practical.

[denton-scratch]

> Technically, you can stop evolution from happening.

Yeah, but would anyone do that to an entire civilization? Evolution leads to greater 'fitness' - improved adaptation to the environment. The travellers are jumping from $HOME_PLANET, into a generation ship, onto a new planet presenting novel adaptation challenges. That planet's star-system then eventually sets off on a long journey, until it encounters a new star. Each of these stages takes many times the time humans have existed on Earth. If you consider only modern humans, we've only been around for 50,000 years, maybe.

And "modern humans" isn't a civilization; it's really all of the different, successive human civilizations.

If you could imagine that, in addition to making stone tools and animal-hide clothes, neanderthals had also learned how to freeze evolution, do you think those guys would be well-adapted to a planet-hopping future? I don't.

[V-2]

Once you have the technology to freeze evolution, you also have the technology to accelerate it and steer it, and given the level of incentive (to gain competitive advantage), I don't imagine it would be a balanced sword-and-shield race in the long run. The "conservatives" couldn't keep up with the "modernists", unless it's some sort of a totalitarian system.

There's been this great (relatively) short story, both humorous and profound, by Stanisław Lem; "The Twenty-first Voyage" in "The Star Diaries". It's based on that exact premise.