Question

for a population to evolve, there must be genetic differences between organisms in that population. these differences arise by
mutation.
common descent.
natural selection.
a change in an organisms behavior.

Explanation:

Genetic differences in a population that drive evolution arise from mutations, which are changes in the DNA sequence. Common descent refers to shared ancestry, natural - selection acts on existing genetic variation, and a change in behavior is not a source of genetic variation.

Answer:

A. mutation