In order for Darwinian natural selection to cause evolutionary change, a population must contain individuals that differ hereditarily in some characteristic because

A) in a population without this kind of variation, the species is doomed to extinction.
B) when all individuals have the same genes, then all individuals are exactly alike in all respects.
C) uniform populations are evolutionary dead ends.
D) unless there is variation of this sort, parents cannot pass on their advantageous attributes to their offspring.