How Could the Appearance of a Version of the Hunger

How could the appearance of a version of the hunger hormone, ghrelin, which also stimulates the learning and memory centers of the brain, lead to natural selection?

A) Any individual with the "old" version of ghrelin dies so only those with the "new" version reproduce. The "old" version of the gene for ghrelin is removed from the population.
B) Throughout its life, an individual with the "new" version of ghrelin becomes better at finding food when hungry, and it teaches these skills to its offspring.
C) Individuals that are able to find more food have more resources and produce more offspring. As a result, the "new" version of ghrelin becomes more common in the population.
D) When faced with a period of extended drought, a large part of the human population died without regard to their genetic makeup. Many of the survivors happened to have the "new" version of ghrelin and therefore, the gene became more common in the population.