Civilization: How to make it happen under the sea.

[MisterMan]

There's a whole lot of civilization to go through before your get sufficiently advanced technology to render a primarily aquatic amphibious species sufficiently comfortable on land so as to live there full time. That's a milestone present-day human technology hasn't yet crossed at the very least.

That’s precisely why I suggest that they would adapt physically to the more successful environment before becoming industrialized to the point that physical adaptation to dry living ceases. I’m suggesting physical mutation, not technological adaptation. Becoming amphibious is a presumably biological change, and would trend toward more full-time land dwelling than anything else. You can’t become amphibious with sheer technology, although there’s a famous short story attempting that.

Food storage is an excellent topic. Presumably they need external storage and transference of chemical caloric energy so that their members can become specialized in their pursuits. In an oceanic environment, this must be done with living tissue and not with dehydration, refrigeration, or other methods of “dry storage.” It’s called that for a reason, after all. And it must be available locally where civilization is developing, preferably in portable form. I say this to forestall irrelevant discussions of how there’s ice in some parts of the ocean. That is similar to discussing cooking with thermal vents.

[Mechalich]

That’s precisely why I suggest that they would adapt physically to the more successful environment before becoming industrialized to the point that physical adaptation to dry living ceases. I’m suggesting physical mutation, not technological adaptation. Becoming amphibious is a presumably biological change, and would trend toward more full-time land dwelling than anything else. You can’t become amphibious with sheer technology, although there’s a famous short story attempting that.

Except cultural and technological change tends to vastly outpace biotic evolution, usually by orders of magnitude. Any hypothetical amphibious sapient species that uncovers the ability to utilize land-based tools is going to advance up various tech levels without undergoing any major physical alterations.

The general scenario here would be if something that is primarily aquatic but capable of limited and fairly awkward terrestrial locomotion acquired sapience. A good example might be Sea Otters. They're socialable, capable of fine manipulation, and even tool-using, exactly the sort of traits that might lead to intelligence. And while they can and occasionally do move about on land, it's clearly not something they handle well. Such a sapient species might utilize greater land-based resources one generation after another while still remaining almost wholly aquatic.

[MisterMan]

No, you’ve got it wrong there. Your example reinforces my point. That’s an example of a land-based creature going to water, and as you have noted, they are now more adjusted to water than land.

I think we can agree to a conclusion: these are narrative decisions. The truth is that we have no mechanism nor adequate explanation for the elevation of animal intelligence to higher-level reason. The “Use of tools” explanation falls just as flat as the old “we came out of the trees” explanation. Fish and birds and most everything else uses their environment as tools, even portable specialized items. We keep finding more and more of it.

The truth is that we just want a “how;” the “why” is that an aquatic human equivalent serves the narrative goals of the author.
Edit: what I mean to say is, what development path serves the story(s) we want to tell?