R.C. Christian wrote
What if an Arkian couple gives birth to a retarded child? Will they ostracize or kill the kid?
The retarded child may be retarded for non-genetic reasons. Presumably retarded Arkians would have a harder time finding Arkian mates, so they would eventually leave the gene pool.
What if someone organizes another alternative gene pool? Will all the alternative gene pools be at war with each other eventually?
The probability of someone organizing another alternative gene pool is so low that it isn't worth discussing.