In SNW 1x09 All Those Who Wander, the crew reenact Aliens with a handful of baby Gorn as their adversaries. We learn that Gorn breed by infecting a host animal with eggs, which hatch and burst out of the host when mature (which can take months or hours, apparently depending on the host). The babies are immediately hostile to other baby Gorn, and are left to their own devices until they are picked up by adults at some indeterminate point. We also learn that these baby Gorn are themselves capable of implanting eggs in a host by spitting on them.
These baby Gorn seem like a full fledged viable species already: small, vicious hunters who are (like tribbles) basically born pregnant. From an evolutionary perspective, that’s plenty to propagate their own existence. It’s also a lifestyle that selects for intelligence (small hunters tend to be pretty smart) but seems like an unlikely route to developing genuine sapience. We’d expect these baby Gorn to have a relatively stable population given the turnaround times of egg maturation and their predilection towards cannibalism, and the later feature would also make it far less likely that any given individual would survive long enough to become an adult, as each fresh generation brings a wave of fresh adversaries who vastly outnumber the handful of survivors from previous waves.
Of course, we know there are adult Gorn. So, how did they come to be? Why would there be a species where the adults are intelligent and social enough to be a spacefaring power, and yet apparently nothing they learn as an adult is needed for an individual to pass on it’s genes?
Do they? In the wild, the babies burst out of a host and are immediately capable of running around and spitting on things, which become infected and eventually babies burst out, onwards and onwards.
The Gorn practice of having separate breeding spaces is clearly an artificial construct designed (presumably by the Gorn themselves) to make it possible to have a functional civilization of adult beings. In the wild, anywhere that has viable hosts is a viable breeding area, and these creatures could not possibly have evolved this life cycle without viable hosts commonly available to them.
The nature of the Gorn seems to dictate that they run out of viable hosts quickly. I imagine the adults have always tried to disperse their children, even back on their home world. Eventually, they probably hit a wall, had a major population bust, and were forced to start exploring space for new breeding grounds so they didn’t die out