Child: Why do birds fly south in the fall?

Adult: If they stayed here over the winter months, they would die of starvation.

Child: How does a bird know that?

Adult: Instinct tells it to leave at the approach of winter.

Child: What is instinct?

Adult: It's the voice inside a bird's head that says, "Fly south or die."

Child: So instinct wants the birds to survive?

Adult: Instinct just delivers the message of natural selection.

Child: What is natural selection?

Adult: It's a process in biology that determines which birds will survive.

Child: So natural selection wants to keep the birds alive?

Adult: You're trying to ascribe human feelings to a process. Natural selection merely accomplishes the work of evolution.

Child: What is evolution?

Adult: It's the system through which all creatures develop from a lower state to a higher state.

Child: Then evolution wants the birds to survive?

Adult: Honey, evolution is an impersonal force, guided by the genes.

Child: What is a gene?

Adult: A unit of complex protein molecules that carries information about heredity.

Child: So genes want the birds to survive?

Adult: Genes don't have opinions. They bum a ride with a bird to transport themselves into the next generation.

Child: If nobody cares about the bird, why should it haul genes around? That's a lot of work.

Adult: We have to assume that a bird would rather live than die.

Child: Why would it care?

Adult: That's a childish question.

Child: I'm a child.