When does life begin?

Human life, that is. At conception? At heart-beat? At brain activity? At first breath of outside air? When they move out of their parents’ house?

FORBIDDEN TOPICS in this thread include:
– abortion
– Constitution
– legal interpretations in general
– political debate

When do you think human life begins? Why?

What are some exceptions to your rule? Are there limits as to where/when that applies (example: On House last nite, the fetus was attached to the woman’s intestine… hence outside where it’s supposed to be).