There’s a simpler explanation to all of this that you may have forgotten from High School Biology. Individuals do not evolve, populations do. Therefore, there can not have been a single Adam or Eve (or Homo sapien couple) which gave birth to the rest of mankind, it was a process that involved many generations. You can be devout and still believe that Adam and Eve were the great^1000000 granparents to man-kind, but you reject that principle of evolution. A single genetic mutation can manifest itself within a population, but it is only until it becomes predominant and characterizes that population does a new species/phenotype become apparent.