It seems obvious that Luke Skywalker defeating Emperor Palpatine in the original Star Wars trilogy was a good thing, but upon taking a look into the origins of the Jedi and the Sith, it seems as though Luke accidentally destroyed the last trace of an ancient Jedi science by beating the evil Emperor.
In the ancient past of Dark Horse Comics' Star Wars canon, the Jedi and the Sith were one order dedicated to the true balance of the Force. This order was called the Je’Daii, and while it was more similar to the era of the prequel trilogy’s Jedi Order than it was to the Sith, there was no real distinction between the Light and the Dark Side of the Force, as any imbalance at all meant total calamity. This lesson was actually a literal one as the world they lived on had two moons, one light and one dark, and if they were out of balance, the world of the Je’Daii would effectively be no more. This means that the practices and sciences of the Je’Daii influenced both the modern day Jedi and Sith in different ways–including one particular practice that only Palpatine seemed to remember.
Palpatine Practiced Genetic Manipulation, Just Like Star Wars’ Je’Daii
In Star Wars: Dawn of the Jedi - Force Storm #2 by John Ostrander and Jan Duursema, readers are taken to the time of the Je’Daii and shown the day-to-day of this ancient order. As shown on one of the opening panels of this book, the Je’Daii sense something deep within a chasm in their world that is interfering with their senses. Everyone who went down to investigate didn’t survive, and any machinery they used was destroyed before anything was learned. So, the Je’Daii used a new form of Force-science that allowed them to genetically alter living creatures in a way that better served the Force. In this issue, readers see the Je’Daii using a Rancor-Dragon–a creature of their own creation–to try to enter the chasm and find out what is down there.
It wasn’t as though the Je’Daii were mad scientists, creating unholy abominations just to see if they could–they were guided by the Force in their efforts. It was almost like they were given permission to alter and speed up evolution in a way that wouldn’t naturally occur (at least, not for a very long time) but also in a way that wasn’t outstandingly unnatural. What they did, they could only do with the blessing of the Force–that’s how intune the Je’Daii were with the cosmic current. That being said, Emperor Palpatine did not abide by the guidelines of the Force. Palpatine was able to create new life through genetic manipulation as well, with Snoke being the prime example–though there were other monsters created by Palpatine’s hand throughout the events leading up to the original trilogy. However, unlike the Je’Daii, the Emperor’s experiments were unnatural, as they were made with nothing but the Dark Side of the Force–and that concentrated dark energy totally corrupted this ancient practice.
While Palpatine certainly bent the genetic manipulation practice to his will, he was still the only Force-user in the modern era that pulled it off, or even recognized it, for that matter. That means that when Emperor Palpatine was defeated by Luke Skywalker (and then permanently by Rey), every known trace of this practice, corrupted or not, was lost to time within the Star Wars universe–and this ancient Jedi science was effectively destroyed forever.