User blog comment:CNBA3/Essence Manipulation/@comment-4867780-20130316095558

"Essence" in this context relates to specific genetic informations, species with unique features that may help strengthen the swarm are assimilated, their secrets decrypted and integrated to the Zerg sub species that venefit the most from them.

So despite the word, it is all a very biological process. Still, the processes involved are extremely advanced complex, and limited to evolution alone, so it may still deserve its own page.

By the way, did you reach the mission in which Kerrigan materialized a unique Zerg life form out of thin air ? That seemed like a never seen before creative combination of psychic power and genetic engineering. I'm sure this power is unique enough to deserve it's own page, something like "Biokinetic Creation".