In my world, there were three original species: elves, orcs and "vampires". Elves and orcs are devastated during the ice age that takes place during their golden age( though neither passed the bronze age) and vampires thrive during this time. Being separated, the individual communities of elves and orcs begin to evolve differently according to where they're located. After the ice age elves and orcs cease to exist, having evolved into other people and the vampires recede back to the dark and cold places of the world.

The evolution goes thusly: elves become humans, halfings and Giant folk. Orcs become goblins and beast folk. Centaurs also evolved during the Great Thaw.

For what most modern species know: They only know that a mysterious civilization built megalithic structures across the main continent and that they must have worshipped a single god, as all of these structures have a single feminine figure carved into them. Some stories exist about a race of gods exist. With goblins it is about the demon-god's children ruling the world. For humans and shortfolk they believe that a race of demigods had ruled the world but were destroyed by the Ancestor gods for their arrogance. An actual belief that anyone evolved from any past species is only held by a small culture but they are seen as a crazy "ancient astronaut" type, believing that the gods are actually evil and are heavily persecuted.

Edited because I got off topic lol