The zerg were native to Zerus, a hostile ash world near the core of the Milky Way. The first spawning pool on Zerus was the catalyst for the creation of the zerg. The pool split the genetic information ("essence") of the proto-zerg that entered it. The proto-zerg competed within; those that ate their counterparts evolved, and became the first zerg. The practice of evolution by consumption, and the principle of survival of the strongest, were fundamental to the zerg. The zerg were minature insectoids and the most insignificant lifeform on the planet. In this form they were discovered by Amon and his xel'naga, who were an ancient extra-galactic species who sought to manipulate the creations of their brethren in order to create host bodies that could end the Infinite Cycle. The Infinite Cycle