Genesis Pits were sites where the Invid Regess conducted her evolutionary experiments, which was part of an Invid plan for universal domination. Through these studies, the Regess was able to determine the ultimate form suitable for her species.
The Invid followed an unusual evolutionary track, where each stage began being disembodied from their mecha. After undergoing genetic programming, they were then transmuted into their new form and inserted into new mecha. While disembodied, they were their unique self, unadorned, without idenity, awaiting transmutation to the next step upward in the spiral of protogenetic progress. Through the use of protoculture, the Regess was able to transmute the Invid bodies into any form she desired.
Since arriving on Earth, the Regess created closed environments to test how each dominant species before humanity functioned, their strengths and weaknesses, as part of the Invid's path to enlightened evolution. Scott Bernard's group of Robotech freedom fighters stumblied into one of these genesis pits, and discovered that it was filled with dinosaurs from a variety of prehistoric ages living together under Invid observation and supervision.
The Regess came to believe she had discovered both the best lifeform for survival on Earth, and the ultimate lifeform with which to one day rule the universe: the human form. She began the first steps in biogenetically transforming her entire hibernating population into this form and equiping them with a new, more powerful mecha. The first of which was Sera, Corg, and Ariel. Many would follow throughout the Third Robotech War.