Rutan healing salve

 was used to fix damaged Rutans. Because they had an unstable cell structure (which was how they were able to shapechange), the salve needed to be similarly unstable. When used on non-Rutans, it could create hybrids by fusing disparate species into a viable new creature.

Percival Ross obtained some of the salve when a Rutan ship crashed in England in the late 19th century. He used it to make human-dolphin hybrids using children, and seals with enhanced intelligence to serve as guards over them. (PROSE: Evolution)