So in the past, if your civilization used the Atlantean technology prior to the collapse and were in the vicinity and survived, your descendants retained their human form along with some other abilities? If your society was not using the tech or on the outskirts, then you devolved into the Fisherman, Brine and the Trench Dwellers? I get the colony on the main land, however wouldn't everyone evolve into some form of fish person? I think the tech sort of preserved the human kingdoms as they are after the collapse, while other kingdoms with limited or no access devolved. It wasn't really explained and only briefly mentioned in the film.