"My beautiful bestiary" -David to Oram.
During the ten years spent on Planet 4, David began to experiment with the Chemical A0-3959X.91 – 15 mutagen. David discovered that some of the species created or mutated by the virus had the potential to further spread a version of the agent via their own refined method of parasitically attacking and infecting a host.
A parasitic wasp was one of the first and came from an egg, the origins of which are unknown. Further experiments of the wasp led to the creation of other parasites that resembled Facehuggers as well as other creatures that possessed a typical adult Xenomorph appearance.
The failed experiments
"You engineered these things David?" -Oram questioning David.
Before achieving what he considered success, David created many different forms of what would eventually become the Xenomorph strain, the previous experiments were proped up in his workshop in each of its different "life-cycle" states with various xenomorph-looking eggs in different sizes ranging from the typical size to that of a golf ball. Creatures resembling deformed facehuggers and neomorphs were placed throughout the workshop. The majority of the experimental creatures consistently had a swept back head.
Experiments on Shaw
For reasons yet to be explained, David at some point dissected and experimented on Shaw's body, mutilating and deforming it in the process. From what he learned or took from Shaw is also unknown.
"What are they waiting for David?"
By the time the Covenant crew arrived, David had created what he deemed successes, the creations in question being large organic ovoid objects, revealed to be Ovomorphs though slightly different in shape and size to typic Xenomorph eggs. Without any living hosts to use, David's project stagnated. After leading Oram into a chamber where he had kept the eggs, his latest experiment was able to progress as a Facehugger from one of the eggs attacked and impregnated Oram, who soon after birthed what David considered a perfect organism.
- During the workshop scene in the novel, David reveals that his creations are not entirely original and are copies of what Engineers created.