well if you want to get technical... the simple fact that cells are dividing proves life. from zygote to embryo- there is life. cells are living. so you are living far before you ever have a heartbeat.

and if you aren't a "human" at that stage, what are you? just because you don't have a heartbeat doesn't mean you are a sheep or a crocodile. we are always humans, we just aren't necessarily always PEOPLE.