Would underwater civilizations be possible?

I don't think so. There could be some super-smart civilization somewhere in the depths of the ocean, but it wouldn't be a human one. It would be some other intelligent species.

If it can breathe underwater, it doesn't have our respiratory system. If it can survive without fire(or sunlight) it has a different digestive system and, consequently, a different means of energy-absorption. If it can swim, it has a different body structure. Because of all that, and probably a few other reasons, it couldn't be any form of primate.

But I'm still completely open to the idea of some other intelligent underwater species that may have a similar societal structure to our's.

Not in my opinion, having read many books on evolution and astrobiology.

A previous answer follows: It was a very specific set of circumstances, involving the many different environments of the giant Rift Valley, in East Africa, more than 15 million years ago, accompanied by multiple ice ages which created the conditions which enabled arboreal prosimian like animals to evolve into semi arboreal primates.

As the forests dried, and thinned out, they had to spend more time on the ground, in the lightly wooded grasslands, savannah, and swamps, foraging for food, and using simple tools, such as rocks, to crush the skulls of kills left by the big predators, to access the brain, and smash bones for their fatty marrow.

It is extremely improbable that such a set of circumstances would ever occur again. Even when it did, humans and their neanderthal cousins shared the same, very basic tool kit for 100,000 years, and it was only an extreme ice age that forced early humans to cope with the new conditions, by refining and improving their tools, around 70,000 years ago, as evidenced by a cave near the beach in South Africa.

Technology remained simple, even after the smelting of copper, then bronze, and finally, iron. It took the Renaissance and Reformation to provide the conditions in which science could take root, then the steam engine. Earth's early civilisations, such as the ancient Egyptians, Babylonians, Romans, Aztecs, Incas, and Mayans, etc. were not technologically oriented, and those in the Americas lacked the wheel. ~~~

There needs to both the capability for, and a payoff to go down the evolutionary path to technology, and civilisation. It only happened once, due to exceptional sets of circumstances, on land, where conditions were somewhat conducive during various the time periods.

Dolphins have brains larger than humans; octopuses can grasp and manipulate, are highly intelligent, and can move on land; ( check out: http://www.google.com/search?q=octopus%3B+move+on+... ) watch the video, but both are highly adapted to their environments, with little pressure to go down that evolutionary path, and even less capability.

only be building air domes underwater

whales and dolphins come close but still have to come up for air

there is no doubt that the control of fire is one essential to our civilization

were we human before we controlled fire? hard to tell. cooking massively changed the kind of food we ate

only in fantasy...and evolution..which is fantasy