We are kind of talking apples and affadavits, here. "Human being" is a biological term, right, member of the species homo sapiens. "Person" is a legal term referring to someone's (or some corporation's) status as a legal entity.

I would say "human being" begins the moment there is unique DNA, and continues until the corpse is completely decomposed. One starts as an embryonic human being, is born and is a living human being, dies and is a dead human being.

Personhood, however, only lasts from birth until death.

Freki