''Rather, it is considered an extinct close evolutionary "cousin" to the direct ancestors. This may not always be the case, though, as some fossil species are proposed to be directly ancestral to others, like how Australopithecus anamensis is most likely to be ancestral to Australopithecus...
As far as I am concerned spiritual matters may be curious, but not substantial enough to construct a worldview on. Philosophy is well to be fair, sometimes useful. It is the mother of science, but a very irrational mother at times. Science is the King's Highway.
A. Mutation is part of evolution by natural selection, without mutation there would be no evolution full stop. It is mutants that are naturally selected against or for.
B. Migration?
C. Genetic drift, far enough. We understand that well enough.
D. Sexual selection is part of natural selection...