How can rebirth occur without sex & parents?

I read the following on the internet: > The birth that is going to take place, by which I mean the past life > of the being that is going to take another birth, will do so > regardless of one deciding to have children or not. Now I have read in the suttas & Visuddhimagga certain actions respectively lead to the respective godly, human, animal, ghost & hell realms. The Visuddhimagga appears to explain how only spontaneous birth in certain heavens & hells has no physical component. Thus spontaneous birth ([opapātika](https://www.wisdomlib.org/definition/opapatika)) is often defined as 'birth without parents'. Therefore, if many people chose to follow the Noble Eightfhold Path and be celibate, how will the past life beings (destined by their kamma for the human world) be reborn if there is a limited supply of embryos? Will there be more twins, triplets, etc? What do various Buddhist texts say about this question?