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.