Brian brings up a point in an earlier comment thread. I'll clarify as to why I believe the way that I do:
It's seems quite evident to me that humankind (or hupersonkind, If Your Name Is Amanda) is set aside from other beings in creation. If one believes in a Creator, which I do, it's probably easier to see this point; that mankind is special, and was created that way.
This is why most civilized people have turned away from what we perceive as less moral practices, such as slavery, and the notion that one person cannot legitimately own another, or deprive another of life or property. It is why murder and theft are outlawed pretty much across the board throughout civilization.
Since it's a difficult call to say at what time a human life holds lower status than a lizard or dog, I have to presume that humans are humans from the point of creation because they are created accordingly. Seems easy enough to me.
After accepting the higher creative status of humanity the issue then becomes personhood. When is a person a person?
After several arguments, I discovered there is not a single demarcation point in the life of a human being that can't be refuted. They are all arbitrary, based upon whatever agenda is being pressed.
So, it brought me to the belief that the only true and morally honest point of where personhood begins in the life of a human being is the moment when that human being comes into existence in human form: conception.
I find that those who like to claim the feminist mantra of 'respect for all persons' often like to draw an arbitrary line of demarcation so as to justify all abortions as righteous acts. It reminds me of those I read about in history books who wrote that "All men are created equal" while denying 'man' status to those they held title to.