It’s an unfortunate trope of the early 20th century wierd pulp fiction Wan & Co. were clearly drawing from for Aquaman. The copy of Lovecraft’s “The Dunwich Horror” on the coffee table in the first scene is a big tell that that’s where we are going: HPL, Robert Howard, Edgar Rice Burroughs, all that lost continent, ancient civilizations, elder monsters from the deeps, etc. stuff. And in all that it’s common to have the “degenerate race” of people who have become bestial in some way — apelike, fishlike, whatever — except for the ruling family or caste who have remained human by keeping their bloodline untainted. And as you would expect it’s often horribly racist. In Aquaman it’s wisely reduced to little more than a plot device. I can live with that.