Answer:
(a). directed by genes.
Step-by-step explanation:
Natural selection can be defined as a process, by which organisms having favorable traits have more chance to survive and reproduce. Due to this, organisms with traits, which are adaptive for a given environment increase with each generation.
Organisms having favorable genes for a trait or behavior will have more chance to survive and pass these genes to next generations. Over time, natural selection will allow the organisms with favorable genes to adapt to their surrounding environment. Hence, for a behavior or trait to evolve under the influence of natural selection, the trait should be directed by genes.
Thus, the correct answer is option (a).