Soul did not come to us by a revolution, but it was an evolutionary process that took place somewhere between the end of the 1950s and the early years of the 1960s. In being evolution, therefor we might consider the Ace/Kent series Birth of Soul as the RnB equivalent of Charles Darwin's Origin of species.
New artists take over the place of the established ones. A good example of this you find on this record. Soul as the major genre in popular Afro-american music took the place that Doo-wop previously hold. Therefor you will find on this record songs by Doo-wop artists as the Drifters who are (unsuccesfully) trying to adopt their own style to the new circumstances, and you will also hear Solomon Burke who steps out of the traditional gospel mode to become a Soul superstar.
The Birth of the Soul series covers this evolutionary process very good. And as in all evolutions it is some kind of "learning by doing" process and it is therefor very interesting listening to those early attempts of what would become a fully devoleped musical genre in a couple of years time.