1) There must have been one that evolved first. Without the first one then the population could never have been produced. I understand your thinking in that the population changed but there must have been that first one that changed just little.
2) Even thinking the populations evolved, there still ought to be transitional forms. And if you believe the populations evolved, there ought to be millions and millions (and that's a conservative number...I'm proud to be a conservative Christian

) of transitional fossils.
Gradual or not there ought to be fossils, and many of them, where we can see intermediate bodies.