hyzmarca: I'm 99.9% certain humans, along with Vorlons, evolved. It's the same thing that happens to the race the Soul Hunters capture in 'River of Souls'. They had evolved into beings of light and then the Soul Hunters nabbed them. I wouldn't go by those Mongoose books for anything canon.
Spontaneous species-wide transformation like that isn't evolution, its revolution. That shit doesn't happen naturally, it requires some sort of intentional technological catalyst.