How did Simelan Evolve?
Jacqueline Lichtenberg's response to a question by Marion Zimmer Bradley.
(Source: Index card file.) It does not just evolve at changeover. Jacqueline agrees that simes or Gens brought up with the opposite language don't ever learn the other fluently, however, because simes in their First Year after changeover have an adaptability quotient of five to ten times greater than an Ancient or "normal" person, this gives them the ability to learn the new language quickly. If they didn't have an adaptability quotient that high, they didn't survive.
Since Jacqueline doesn't want to resolve how the simes came into being, at this point, she can't say exactly how the language developed, but she leans to a theory that it's the first successful artificial language ever constructed.