So we don’t know if evolution works in the warcraft reality like it does irl aka through genetic inheritance, survival, and mutation.
However all evolution means is “change over a long period of time”
Many races have encountered this.
Humans are descended from vrykul who themselves are titan constructs who got the curse of flesh. Dwarves, gnomes, troggs, etc share a similiar origin.
Orcs are descended from orgres, who are descended from gron, etc, etc until you go all the way back to the living mountain created by a titan.
All elves are descended from trolls. There are also countless different troll tribes so who knows what the OG troll tribes looked like. In addition to elves, Naga who were elves also descend from trolls.
The animalistic races like tauren, vulpera, and pandaren are believed to be descended from the ancients/wild gods who are massive sentient animals. Though the exact mechanism of this is not known.
Goblin and giblins share a heritage although it is unknown if one came first or if they both came from the same ancestor.
The dragon aspects were artificially “uplifted” by the titans as a “reward” for defeating galakrond.
While the Draenei are not known to have a previous form the broken and lost ones are Draenei who were transformed by the red mist bio-weapon. It is unknown however if they can have children, and if they can if they would be broken or if they would be uncorrupted Draenei.
Worgen are the result of combining the essence of a wild god (goldrin) and humans (titan construct descendants.
Dracthyr are the result of combinding the essence of dragons with the essence of mortals. What mortal race or races were used are unknown. Although neither humans nor elves existed at the time. So most likely option includes trolls, and vrykul or perhaps a race that existed 20,000 years ago but has since gone extinct.