That would depend on what do you nean by races or spcecies.
This world is about fantasy by the way but to try to answer your question.
Exemple Elves. there are quite a number of elven sub-races gold,noon,green,sea,avariel, lythari and drow. they all come from a original elf race, the high elf.
species: elves come from, acording to their legends, the blood spilled from a battle bettewn Corellon Larethian(the leader of the seldarine, the elven gods) and Gruumsh(a main orc God)mixed with tears from Sehanime Moonbow.The orcs.....I don´t have anyting on them,but loking from the previus information there are not related. And humans, like us in this planet they evolved.There are different species not races.
"He who fights with monsters should look to it that he himself does not became a monster... when you gaze long into the abyss the abyss gazes into you..."
- Waterdeep city constrution.
- Shadowdale low level adventure module.
- Rashmare /Thay high level adventure module.