Really, there's no reason a Wylder couldn't be born from any other race. There are no Punnett's Squares in Fortannis and with magic in the mix, ¿who's to say what's bouncing around in the stork's bundle? With the prevelance of Race Change Rituals, flaws with the same effect, and good old Black-Box Magic, it's likely that the body holding a given spirit was not the body when that spirit was first born. ¿Do offspring follow the body or the Spirit of their parents? Who knows? And, since the ARB is silent on the matter, it's all up to Local plot and player imagination.