"So are "Birth Defects" the driving force of evolution, or not? "
Huh? Uh, no. I had blond hair when I was young. My brother had red hair. My sister had black hair. That's genetic variation. Genetic variation drives evolution, along with the need to survive and reproduce in the existing environment.
You really should read an elementary level book on the theory of Evolution. I will help you not to appear ignorant in your messages. Ask the librarian at your local public library to recommend one for you.
Sure I can understand variations on a theme, hair or eye color, but the creation of new species, of new organs takes much more than a minor variation. It takes a lucky mutation, (ok even a lucky series of mutations over a very long time), most of the mutations that occur today also have another name, birth defects.