Concept:Mutation is the ultimate and primary source of new genetic variation in any population.
Explanation:A mutation is a spontaneous, random change in the DNA sequence of an organism's genome.
This change introduces completely new alleles that did not previously exist in the population.
These novel alleles provide the raw material upon which evolution can act.
Natural selection and genetic drift only alter the frequency of alleles that are already present; they do not create new genetic variations.
Gene flow can bring alleles from one population into another, but it cannot generate a brand-new allele.
Only a mutation can produce a truly original trait or gene variant.
Therefore, mutation is called the primary source of variation because all other evolutionary forces simply rearrange or select existing variations.
Without mutation, a population would have no new genetic material to adapt to changing environments.
Answer:B. Mutation