Let's say you're a member of a dwindling race. Only a few thousand of your kind left. Millenia of genetic tampering have ruined your own genome. Your only hope for survival is a fresh infusion of genetic material from a compatible donor. However, the only donors available happen to have a 20,000 year evolutionary disadvantage, compared to your people. It would be akin to having a bonobo liver transplanted into a human body.
You decide to tamper with the genetics of those lesser cousins to your species, in order to bridge the genetic gap. However, with your limited numbers, keeping track of favourable and harmful traits among a fluid population of billions is logistically infeasible. Instead, you devise a test involving attaching a pigment to favourable genetic markers in the test population. You wrap the test in superstition and folklore, and teach your test population to self-administer it. The test becomes a ritual. Those conducting the test have forgotten its actual purpose. You teach them which marks are "good" and which are "evil" and they self-segregate across un-counted generations according to your directives.
That's my Voluval theory. Freakin' Joves trying to hollow us out and use us for canoes.