In my last post I shared my thoughts on the "medusas as curse" concept from D&D 5e. In this post I want to touch on the other depictions in D&D of medusas as a self-reproducing race. (For reference going forward, I'm using "gorgon" as a gender-neutral term for medusas and co.)
In Greek myth, there's no apparent depiction of gorgons as a self-reproducing race. There was a trio of sisters, the Gorgons, born to Phorcys and Ceto. One of the sisters, Medusa, gave birth to Pegasus and Chrysaor after being impregnated by Poseidon. At most, one fragmentary account says Medusa's father was a gorgon. (For reference, "gorgon" in Greek translated to "terrible one, fierce one.")
In D&D, Gygax and co took various unique monsters from mythology and gave them ecologies where each was made into an entire species. These ecologies were often weird, nonsensical, or even misogynistic. In the case of the medusa, their reproduction actually changed across the editions due to differing writers and sometimes it was just plain weird.
Initially the medusas received no information on their reproduction, then later publications started providing more information, then contradicted themselves later on. Some said most medusas were female (implying there were a few males for reproduction), others said medusas were always female (raising the question of how they reproduced).
One 1986 article introduced a new monster called the "maedar" as the male counterpart of the medusa, whose appearance and powers were basically the inverse of his female counterpart: he was bald and turned stone to flesh with his touch. These gorgons reproduced more or less normally for sexually dimorphic humanoids. In a subsequent 1993 book this simple reproduction was needlessly complicated by the writer claiming that only 1% of offspring were maedar, while the other 99% were human infants that petrified upon seeing their mother. In order to birth more medusas, the medusa had to rely on human men. What kind of sense does that make?
In a 3rd edition Dragon magazine article, issue #355, they were given a much more sensible method of reproduction. Gorgons reproduced normally among their own kind, although maedar were born rarely compared to medusas. Otherwise, medusas could abduct human men for reproduction: such pairings produced infant medusas, as well as human boys who petrified upon seeing their mother.
In 4th edition, the maedar were simply called male medusas and their abilities changed to a weaker form of the female's: he was still bald, but now his gaze was literally venomous.
There's no maedar in 5th edition due to their nature changing to a curse, but unofficial conversions combine the pre-4e maedar with the 4e male medusa so that he is bald, has venomous gaze, and turns stone to flesh.
So what do I think of all this? Well, I don't think D&D monsters need to have ecologies in the first place. It demystifies them and turns them into alien fauna. How is something a monster when it has a place in the natural ecology? Not only that but, as I said before, a lot of these pseudo-naturalistic ecologies are just silly.
Gorgons don't need to have societies or reproductive cycles to explain where they come from. I'm satisfied with them spontaneously generating as needed by the GM. If you need a more detailed explanation for that, then posit the existence of magic fields that radiate across the world according to the movements of planets. These magic fields occasionally crisscross at symbolic times and locations, where they form magical vents that spawn magical creatures. The medusa is spawned when the magic fields of the Moon are ascendant, as the Moon is the planet sacred to cycles, reptiles, and delirium.
In you want something inspired by mythology, then I have another idea. In Greek myth there is a monster called the Dracaena ("she-dragon, dragoness"), who appears as a beautiful nymph from the waist up and a dragon from the waist down. Famous Dracaena included Echidna and Ceto, who gave birth to various monsters. I'm just gonna call her a "nymph-dragoness" to reflect her appearance. The fantasy world is therefore home to one or more of these nymph-dragonesses. They are legendary monstresses who live to spawn various monsters including gorgons. Where did she come from? The earth gave birth to her. Where did the earth come from? It arose spontaneously from the primordial chaos. Where did that come from? It always existed.